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2.配置简介(MyBatis源码篇)

1 SqlSessionFactoryBuilder

上篇例子中,我们以 SqlSessionFactoryBuilder 去创建 SqlSessionFactory, 那么,我们就先从SqlSessionFactoryBuilder入手, 咱们先看看源码是怎么实现的。 SqlSessionFactoryBuilder源码片段:
public class SqlSessionFactoryBuilder {

    //Reader读取mybatis配置文件,传入构造方法
    //除了Reader外,其实还有对应的inputStream作为参数的构造方法,
    //这也体现了mybatis配置的灵活性
    public SqlSessionFactory build(Reader reader) {
        return build(reader, null, null);
    }

    public SqlSessionFactory build(Reader reader, String environment) {
        return build(reader, environment, null);
    }

    //mybatis配置文件 + properties, 此时mybatis配置文件中可以不配置properties,也能使用${}形式
    public SqlSessionFactory build(Reader reader, Properties properties) {
        return build(reader, null, properties);
    }

    //通过XMLConfigBuilder解析mybatis配置,然后创建SqlSessionFactory对象
    public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
        try {
            XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
            //下面看看这个方法的源码
            return build(parser.parse());
        } catch (Exception e) {
            throw ExceptionFactory.wrapException("Error building SqlSession.", e);
        } finally {
            ErrorContext.instance().reset();
            try {
                reader.close();
            } catch (IOException e) {
                // Intentionally ignore. Prefer previous error.
            }
        }
    }

    public SqlSessionFactory build(Configuration config) {
        return new DefaultSqlSessionFactory(config);
    }
}
通过源码,我们可以看到SqlSessionFactoryBuilder 通过XMLConfigBuilder 去解析我们传入的mybatis的配置文件, 下面就接着看看 XMLConfigBuilder 部分源码:
/**
 * mybatis 配置文件解析
 */
public class XMLConfigBuilder extends BaseBuilder {
    public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
        this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
    }

    private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
        super(new Configuration());
        ErrorContext.instance().resource("SQL Mapper Configuration");
        this.configuration.setVariables(props);
        this.parsed = false;
        this.environment = environment;
        this.parser = parser;
    }

    //外部调用此方法对mybatis配置文件进行解析
    public Configuration parse() {
        if (parsed) {
            throw new BuilderException("Each XMLConfigBuilder can only be used once.");
        }
        parsed = true;
        //从根节点configuration
        parseConfiguration(parser.evalNode("/configuration"));
        return configuration;
    }

    //此方法就是解析configuration节点下的子节点
    //由此也可看出,我们在configuration下面能配置的节点为以下10个节点
    private void parseConfiguration(XNode root) {
        try {
            propertiesElement(root.evalNode("properties")); //issue #117 read properties first
            typeAliasesElement(root.evalNode("typeAliases"));
            pluginElement(root.evalNode("plugins"));
            objectFactoryElement(root.evalNode("objectFactory"));
            objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
            settingsElement(root.evalNode("settings"));
            environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631
            databaseIdProviderElement(root.evalNode("databaseIdProvider"));
            typeHandlerElement(root.evalNode("typeHandlers"));
            mapperElement(root.evalNode("mappers"));
        } catch (Exception e) {
            throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
        }
    }
}
通过以上源码,我们就能看出,在mybatis的配置文件中:
  1. configuration节点为根节点。
  2. 在configuration节点之下,我们可以配置10个子节点, 分别为:properties、typeAliases、plugins、objectFactory、objectWrapperFactory、settings、environments、databaseIdProvider、typeHandlers、mappers。

2 配置文件元素

2.1 元素1:properties

<configuration>
    <!-- 方法一: 从外部指定properties配置文件, 除了使用resource属性指定外,还可通过url属性指定url  
        <properties resource="dbConfig.properties"></properties> 
    -->
    <!-- 方法二: 直接配置为xml -->
    <properties>
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/test1"/>
        <property name="username" value="root"/>
        <property name="password" value="root"/>
    </properties>
那么,我要是 两种方法都同时用了,那么哪种方法优先?当以上两种方法都xml配置优先, 外部指定properties配置其次。至于为什么,接下来的源码分析会提到,请留意一下。

2.2 元素2:envirements

<environments default="development">
    <environment id="development">
        <!-- 
        JDBC–这个配置直接简单使用了JDBC的提交和回滚设置。它依赖于从数据源得到的连接来管理事务范围。
        MANAGED–这个配置几乎没做什么。它从来不提交或回滚一个连接。而它会让容器来管理事务的整个生命周期(比如Spring或JEE应用服务器的上下文)。
        -->
        <transactionManager type="JDBC"/>
        <!--
        UNPOOLED–这个数据源的实现是每次被请求时简单打开和关闭连接
        POOLED–mybatis实现的简单的数据库连接池类型,它使得数据库连接可被复用,不必在每次请求时都去创建一个物理的连接。
        JNDI – 通过jndi从tomcat之类的容器里获取数据源。
        -->
        <dataSource type="POOLED">
            <!--
            如果上面没有指定数据库配置的properties文件,那么此处可以这样直接配置 
            <property name="driver" value="com.mysql.jdbc.Driver"/>
            <property name="url" value="jdbc:mysql://localhost:3306/test1"/>
            <property name="username" value="root"/>
            <property name="password" value="root"/>
            -->

            <!-- 上面指定了数据库配置文件, 配置文件里面也是对应的这四个属性 -->
            <property name="driver" value="${driver}"/>
            <property name="url" value="${url}"/>
            <property name="username" value="${username}"/>
            <property name="password" value="${password}"/>  
        </dataSource>
    </environment>

    <!-- 我再指定一个environment -->
    <environment id="test">
        <transactionManager type="JDBC"/>
        <dataSource type="POOLED">
            <property name="driver" value="com.mysql.jdbc.Driver"/>
            <!-- 与上面的url不一样 -->
            <property name="url" value="jdbc:mysql://localhost:3306/demo"/>
            <property name="username" value="root"/>
            <property name="password" value="root"/>
        </dataSource>
    </environment>
</environments>
environments元素节点可以配置多个environment子节点, 怎么理解呢? 假如我们系统的开发环境和正式环境所用的数据库不一样(这是肯定的), 那么可以设置两个environment, 两个id分别对应开发环境(dev)和正式环境(final),那么通过配置environments的default属性就能选择对应的environment了, 例如,我将environments的deault属性的值配置为dev, 那么就会选择dev的environment。 至于这个是怎么实现的,下面源码就会讲。

2.3 解析方法:propertiesElement、environmentsElement

好啦,上面简单给大家介绍了一下properties 和 environments 的配置, 接下来就正式开始看源码了: 上次我们说过mybatis 是通过XMLConfigBuilder这个类在解析mybatis配置文件的,那么本次就接着看看XMLConfigBuilder对于properties和environments的解析:
public class XMLConfigBuilder extends BaseBuilder {

    private boolean parsed;
    // xml解析器
    private XPathParser parser;
    private String environment;

    // 上次说到这个方法是在解析mybatis配置文件中能配置的元素节点
    // 今天首先要看的就是properties节点和environments节点
    private void parseConfiguration(XNode root) {
        try {
            // 解析properties元素
            propertiesElement(root.evalNode("properties")); //issue #117 read properties first
            typeAliasesElement(root.evalNode("typeAliases"));
            pluginElement(root.evalNode("plugins"));
            objectFactoryElement(root.evalNode("objectFactory"));
            objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
            settingsElement(root.evalNode("settings"));
            // 解析environments元素
            environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631
            databaseIdProviderElement(root.evalNode("databaseIdProvider"));
            typeHandlerElement(root.evalNode("typeHandlers"));
            mapperElement(root.evalNode("mappers"));
        } catch (Exception e) {
            throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
        }
    }


    //下面就看看解析properties的具体方法
    private void propertiesElement(XNode context) throws Exception {
        if (context != null) {
            // 将子节点的 name 以及value属性set进properties对象
            // 这儿可以注意一下顺序,xml配置优先, 外部指定properties配置其次
            Properties defaults = context.getChildrenAsProperties();
            // 获取properties节点上 resource属性的值
            String resource = context.getStringAttribute("resource");
            // 获取properties节点上 url属性的值, resource和url不能同时配置
            String url = context.getStringAttribute("url");
            if (resource != null && url != null) {
                throw new BuilderException("The properties element cannot specify both a URL and a resource based property file reference.  Please specify one or the other.");
            }
            // 把解析出的properties文件set进Properties对象
            if (resource != null) {
                defaults.putAll(Resources.getResourceAsProperties(resource));
            } else if (url != null) {
                defaults.putAll(Resources.getUrlAsProperties(url));
            }
            // 将configuration对象中已配置的Properties属性与刚刚解析的融合
            // configuration这个对象会装载所解析mybatis配置文件的所有节点元素,以后也会频频提到这个对象
            // 既然configuration对象用有一系列的get/set方法, 那是否就标志着我们可以使用java代码直接配置? 
            // 答案是肯定的, 不过使用配置文件进行配置,优势不言而喻
            Properties vars = configuration.getVariables();
            if (vars != null) {
                defaults.putAll(vars);
            }
            // 把装有解析配置propertis对象set进解析器, 因为后面可能会用到
            parser.setVariables(defaults);
            // set进configuration对象
            configuration.setVariables(defaults);
        }
    }

    //下面再看看解析enviroments元素节点的方法
    private void environmentsElement(XNode context) throws Exception {
        if (context != null) {
            if (environment == null) {
                //解析environments节点的default属性的值
                //例如: <environments default="development">
                environment = context.getStringAttribute("default");
            }
            //递归解析environments子节点
            for (XNode child : context.getChildren()) {
                //<environment id="development">, 只有enviroment节点有id属性,那么这个属性有何作用?
                //environments 节点下可以拥有多个 environment子节点
                //类似于这样: <environments default="development"><environment id="development">...</environment><environment id="test">...</environments>
                //意思就是我们可以对应多个环境,比如开发环境,测试环境等, 由environments的default属性去选择对应的enviroment
                String id = child.getStringAttribute("id");
                //isSpecial就是根据由environments的default属性去选择对应的enviroment
                if (isSpecifiedEnvironment(id)) {
                    //事务, mybatis有两种:JDBC 和 MANAGED, 配置为JDBC则直接使用JDBC的事务,配置为MANAGED则是将事务托管给容器, 
                    TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
                    //enviroment节点下面就是dataSource节点了,解析dataSource节点(下面会贴出解析dataSource的具体方法)
                    DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
                    DataSource dataSource = dsFactory.getDataSource();
                    Environment.Builder environmentBuilder = new Environment.Builder(id)
                          .transactionFactory(txFactory)
                          .dataSource(dataSource);
                    //老规矩,会将dataSource设置进configuration对象
                    configuration.setEnvironment(environmentBuilder.build());
                }
            }
        }
    }

    //下面看看dataSource的解析方法
    private DataSourceFactory dataSourceElement(XNode context) throws Exception {
        if (context != null) {
            //dataSource的连接池
            String type = context.getStringAttribute("type");
            //子节点 name, value属性set进一个properties对象
            Properties props = context.getChildrenAsProperties();
            //创建dataSourceFactory
            DataSourceFactory factory = (DataSourceFactory) resolveClass(type).newInstance();
            factory.setProperties(props);
            return factory;
        }
        throw new BuilderException("Environment declaration requires a DataSourceFactory.");
    } 
}
通过以上对mybatis源码的解读,相信大家对mybatis的配置又有了一个深入的认识。还有一个问题, 上面我们看到,在配置dataSource的时候使用了 ${driver} 这种表达式, 这种形式是怎么解析的?其实,是通过PropertyParser这个类解析:
/**
 * 这个类解析${}这种形式的表达式
 */
public class PropertyParser {

    public static String parse(String string, Properties variables) {
        VariableTokenHandler handler = new VariableTokenHandler(variables);
        GenericTokenParser parser = new GenericTokenParser("${", "}", handler);
        return parser.parse(string);
    }

    private static class VariableTokenHandler implements TokenHandler {
        private Properties variables;

        public VariableTokenHandler(Properties variables) {
            this.variables = variables;
        }

        public String handleToken(String content) {
            if (variables != null && variables.containsKey(content)) {
                return variables.getProperty(content);
            }
            return "${" + content + "}";
        }
    }
}
以上就是对于properties 和 environments元素节点的分析,比较重要的都在对于源码的注释中标出。

2.4 元素3:typeAliases

typeAliases节点主要用来设置别名,其实这是挺好用的一个功能, 通过配置别名,我们不用再指定完整的包名,并且还能取别名。 例如: 我们在使用 com.demo.entity. UserEntity 的时候,我们可以直接配置一个别名user, 这样以后在配置文件中要使用到com.demo.entity.UserEntity的时候,直接使用User即可。 就以上例为例,我们来实现一下,看看typeAliases的配置方法:
<configuration>
    <typeAliases>
        <!--
        通过package, 可以直接指定package的名字, mybatis会自动扫描你指定包下面的javabean,
        并且默认设置一个别名,默认的名字为: javabean 的首字母小写的非限定类名来作为它的别名。
        也可在javabean 加上注解@Alias 来自定义别名, 例如: @Alias(user) 
        <package name="com.dy.entity"/>
        -->
        <typeAlias alias="UserEntity" type="com.dy.entity.User"/>
    </typeAliases>

    ......

</configuration>
再写一段测试代码,看看有没生效:(我只写一段伪代码)
Configuration con = sqlSessionFactory.getConfiguration();
Map<String, Class<?>> typeMap = con.getTypeAliasRegistry().getTypeAliases();
for(Entry<String, Class<?>> entry: typeMap.entrySet()) {
    System.out.println(entry.getKey() + " ================> " + entry.getValue().getSimpleName());
}

2.5 解析方法:typeAliasesElement

/**
 * 解析typeAliases节点
 */
private void typeAliasesElement(XNode parent) {
    if (parent != null) {
        for (XNode child : parent.getChildren()) {
            //如果子节点是package, 那么就获取package节点的name属性, mybatis会扫描指定的package
            if ("package".equals(child.getName())) {
                String typeAliasPackage = child.getStringAttribute("name");
                //TypeAliasRegistry 负责管理别名, 这儿就是通过TypeAliasRegistry 进行别名注册, 下面就会看看TypeAliasRegistry源码
                configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
            } else {
                //如果子节点是typeAlias节点,那么就获取alias属性和type的属性值
                String alias = child.getStringAttribute("alias");
                String type = child.getStringAttribute("type");
                try {
                    Class<?> clazz = Resources.classForName(type);
                    if (alias == null) {
                        typeAliasRegistry.registerAlias(clazz);
                    } else {
                        typeAliasRegistry.registerAlias(alias, clazz);
                    }
                } catch (ClassNotFoundException e) {
                    throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e);
                }
            }
        }
    }
}
重要的源码在这儿:TypeAliasRegistry.java
public class TypeAliasRegistry {

  //这就是核心所在啊, 原来别名就仅仅通过一个HashMap来实现, key为别名, value就是别名对应的类型(class对象)
  private final Map<String, Class<?>> TYPE_ALIASES = new HashMap<String, Class<?>>();

  /**
   * 以下就是mybatis默认为我们注册的别名
   */
  public TypeAliasRegistry() {
    registerAlias("string", String.class);

    registerAlias("byte", Byte.class);
    registerAlias("long", Long.class);
    registerAlias("short", Short.class);
    registerAlias("int", Integer.class);
    registerAlias("integer", Integer.class);
    registerAlias("double", Double.class);
    registerAlias("float", Float.class);
    registerAlias("boolean", Boolean.class);

    registerAlias("byte[]", Byte[].class);
    registerAlias("long[]", Long[].class);
    registerAlias("short[]", Short[].class);
    registerAlias("int[]", Integer[].class);
    registerAlias("integer[]", Integer[].class);
    registerAlias("double[]", Double[].class);
    registerAlias("float[]", Float[].class);
    registerAlias("boolean[]", Boolean[].class);

    registerAlias("_byte", byte.class);
    registerAlias("_long", long.class);
    registerAlias("_short", short.class);
    registerAlias("_int", int.class);
    registerAlias("_integer", int.class);
    registerAlias("_double", double.class);
    registerAlias("_float", float.class);
    registerAlias("_boolean", boolean.class);

    registerAlias("_byte[]", byte[].class);
    registerAlias("_long[]", long[].class);
    registerAlias("_short[]", short[].class);
    registerAlias("_int[]", int[].class);
    registerAlias("_integer[]", int[].class);
    registerAlias("_double[]", double[].class);
    registerAlias("_float[]", float[].class);
    registerAlias("_boolean[]", boolean[].class);

    registerAlias("date", Date.class);
    registerAlias("decimal", BigDecimal.class);
    registerAlias("bigdecimal", BigDecimal.class);
    registerAlias("biginteger", BigInteger.class);
    registerAlias("object", Object.class);

    registerAlias("date[]", Date[].class);
    registerAlias("decimal[]", BigDecimal[].class);
    registerAlias("bigdecimal[]", BigDecimal[].class);
    registerAlias("biginteger[]", BigInteger[].class);
    registerAlias("object[]", Object[].class);

    registerAlias("map", Map.class);
    registerAlias("hashmap", HashMap.class);
    registerAlias("list", List.class);
    registerAlias("arraylist", ArrayList.class);
    registerAlias("collection", Collection.class);
    registerAlias("iterator", Iterator.class);

    registerAlias("ResultSet", ResultSet.class);
  }


  /**
   * 处理别名, 直接从保存有别名的hashMap中取出即可
   */
  @SuppressWarnings("unchecked")
  public <T> Class<T> resolveAlias(String string) {
    try {
      if (string == null) return null;
      String key = string.toLowerCase(Locale.ENGLISH); // issue #748
      Class<T> value;
      if (TYPE_ALIASES.containsKey(key)) {
        value = (Class<T>) TYPE_ALIASES.get(key);
      } else {
        value = (Class<T>) Resources.classForName(string);
      }
      return value;
    } catch (ClassNotFoundException e) {
      throw new TypeException("Could not resolve type alias '" + string + "'.  Cause: " + e, e);
    }
  }

  /**
   * 配置文件中配置为package的时候, 会调用此方法,根据配置的报名去扫描javabean ,然后自动注册别名
   * 默认会使用 Bean 的首字母小写的非限定类名来作为它的别名
   * 也可在javabean 加上注解@Alias 来自定义别名, 例如: @Alias(user)
   */
  public void registerAliases(String packageName){
    registerAliases(packageName, Object.class);
  }

  public void registerAliases(String packageName, Class<?> superType){
    ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
    resolverUtil.find(new ResolverUtil.IsA(superType), packageName);
    Set<Class<? extends Class<?>>> typeSet = resolverUtil.getClasses();
    for(Class<?> type : typeSet){
      // Ignore inner classes and interfaces (including package-info.java)
      // Skip also inner classes. See issue #6
      if (!type.isAnonymousClass() && !type.isInterface() && !type.isMemberClass()) {
        registerAlias(type);
      }
    }
  }

  public void registerAlias(Class<?> type) {
    String alias = type.getSimpleName();
    Alias aliasAnnotation = type.getAnnotation(Alias.class);
    if (aliasAnnotation != null) {
      alias = aliasAnnotation.value();
    } 
    registerAlias(alias, type);
  }

  //这就是注册别名的本质方法, 其实就是向保存别名的hashMap新增值而已, 呵呵, 别名的实现太简单了,对吧
  public void registerAlias(String alias, Class<?> value) {
    if (alias == null) throw new TypeException("The parameter alias cannot be null");
    String key = alias.toLowerCase(Locale.ENGLISH); // issue #748
    if (TYPE_ALIASES.containsKey(key) && TYPE_ALIASES.get(key) != null && !TYPE_ALIASES.get(key).equals(value)) {
      throw new TypeException("The alias '" + alias + "' is already mapped to the value '" + TYPE_ALIASES.get(key).getName() + "'.");
    }
    TYPE_ALIASES.put(key, value);
  }

  public void registerAlias(String alias, String value) {
    try {
      registerAlias(alias, Resources.classForName(value));
    } catch (ClassNotFoundException e) {
      throw new TypeException("Error registering type alias "+alias+" for "+value+". Cause: " + e, e);
    }
  }

  /**
   * 获取保存别名的HashMap, Configuration对象持有对TypeAliasRegistry的引用,因此,如果需要,我们可以通过Configuration对象获取
   */
  public Map<String, Class<?>> getTypeAliases() {
    return Collections.unmodifiableMap(TYPE_ALIASES);
  }

}
由源码可见,设置别名的原理就这么简单,Mybatis默认给我们设置了不少别名,在上面代码中都可以见到。

2.6 元素4:TypeHandler

Mybatis中的TypeHandler是什么? 无论是 MyBatis 在预处理语句(PreparedStatement)中设置一个参数时,还是从结果集中取出一个值时,都会用类型处理器将获取的值以合适的方式转换成 Java 类型。Mybatis默认为我们实现了许多TypeHandler, 当我们没有配置指定TypeHandler时,Mybatis会根据参数或者返回结果的不同,默认为我们选择合适的TypeHandler处理。 那么,Mybatis为我们实现了哪些TypeHandler呢? 我们怎么自定义实现一个TypeHandler ? 这些都会在接下来的mybatis的源码中看到。在看源码之前,还是像之前一样,先看看怎么配置吧?
<configuration>
    <typeHandlers>
      <!-- 
          当配置package的时候,mybatis会去配置的package扫描TypeHandler
          <package name="com.dy.demo"/>
       -->

      <!-- handler属性直接配置我们要指定的TypeHandler -->
      <typeHandler handler=""/>

      <!-- javaType 配置java类型,例如String, 如果配上javaType, 那么指定的typeHandler就只作用于指定的类型 -->
      <typeHandler javaType="" handler=""/>

      <!-- jdbcType 配置数据库基本数据类型,例如varchar, 如果配上jdbcType, 那么指定的typeHandler就只作用于指定的类型  -->
      <typeHandler jdbcType="" handler=""/>

      <!-- 也可两者都配置 -->
      <typeHandler javaType="" jdbcType="" handler=""/>

  </typeHandlers>

  ......

</configuration>

2.7 解析方法:typeHandlerElement

上面简单介绍了一下TypeHandler, 下面就看看mybatis中TypeHandler的源码了。老规矩,先从对xml的解析讲起:
/**
 * 解析typeHandlers节点
 */
private void typeHandlerElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        //子节点为package时,获取其name属性的值,然后自动扫描package下的自定义typeHandler
        if ("package".equals(child.getName())) {
          String typeHandlerPackage = child.getStringAttribute("name");
          typeHandlerRegistry.register(typeHandlerPackage);
        } else {
          //子节点为typeHandler时, 可以指定javaType属性, 也可以指定jdbcType, 也可两者都指定
          //javaType 是指定java类型
          //jdbcType 是指定jdbc类型(数据库类型: 如varchar)
          String javaTypeName = child.getStringAttribute("javaType");
          String jdbcTypeName = child.getStringAttribute("jdbcType");
          //handler就是我们配置的typeHandler
          String handlerTypeName = child.getStringAttribute("handler");
          //resolveClass方法就是我们上篇文章所讲的TypeAliasRegistry里面处理别名的方法
          Class<?> javaTypeClass = resolveClass(javaTypeName);
          //JdbcType是一个枚举类型,resolveJdbcType方法是在获取枚举类型的值
          JdbcType jdbcType = resolveJdbcType(jdbcTypeName);
          Class<?> typeHandlerClass = resolveClass(handlerTypeName);
          //注册typeHandler, typeHandler通过TypeHandlerRegistry这个类管理
          if (javaTypeClass != null) {
            if (jdbcType == null) {
              typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);
            } else {
              typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);
            }
          } else {
            typeHandlerRegistry.register(typeHandlerClass);
          }
        }
      }
    }
}
接下来看看TypeHandler的管理注册类:TypeHandlerRegistry.java
/**
 * typeHandler注册管理类
 */
public final class TypeHandlerRegistry {

  //源码一上来,二话不说,几个大大的HashMap就出现,这不又跟上次讲的typeAliases的注册类似么

  //基本数据类型与其包装类
  private static final Map<Class<?>, Class<?>> reversePrimitiveMap = new HashMap<Class<?>, Class<?>>() {
    private static final long serialVersionUID = 1L;
    {
      put(Byte.class, byte.class);
      put(Short.class, short.class);
      put(Integer.class, int.class);
      put(Long.class, long.class);
      put(Float.class, float.class);
      put(Double.class, double.class);
      put(Boolean.class, boolean.class);
      put(Character.class, char.class);
    }
  };

  //这几个MAP不用说就知道存的是什么东西吧,命名的好处
  private final Map<JdbcType, TypeHandler<?>> JDBC_TYPE_HANDLER_MAP = new EnumMap<JdbcType, TypeHandler<?>>(JdbcType.class);
  private final Map<Type, Map<JdbcType, TypeHandler<?>>> TYPE_HANDLER_MAP = new HashMap<Type, Map<JdbcType, TypeHandler<?>>>();
  private final TypeHandler<Object> UNKNOWN_TYPE_HANDLER = new UnknownTypeHandler(this);
  private final Map<Class<?>, TypeHandler<?>> ALL_TYPE_HANDLERS_MAP = new HashMap<Class<?>, TypeHandler<?>>();

  //就像上篇文章讲的typeAliases一样,mybatis也默认给我们注册了不少的typeHandler
  //具体如下
  public TypeHandlerRegistry() {
    register(Boolean.class, new BooleanTypeHandler());
    register(boolean.class, new BooleanTypeHandler());
    register(JdbcType.BOOLEAN, new BooleanTypeHandler());
    register(JdbcType.BIT, new BooleanTypeHandler());

    register(Byte.class, new ByteTypeHandler());
    register(byte.class, new ByteTypeHandler());
    register(JdbcType.TINYINT, new ByteTypeHandler());

    register(Short.class, new ShortTypeHandler());
    register(short.class, new ShortTypeHandler());
    register(JdbcType.SMALLINT, new ShortTypeHandler());

    register(Integer.class, new IntegerTypeHandler());
    register(int.class, new IntegerTypeHandler());
    register(JdbcType.INTEGER, new IntegerTypeHandler());

    register(Long.class, new LongTypeHandler());
    register(long.class, new LongTypeHandler());

    register(Float.class, new FloatTypeHandler());
    register(float.class, new FloatTypeHandler());
    register(JdbcType.FLOAT, new FloatTypeHandler());

    register(Double.class, new DoubleTypeHandler());
    register(double.class, new DoubleTypeHandler());
    register(JdbcType.DOUBLE, new DoubleTypeHandler());

    register(String.class, new StringTypeHandler());
    register(String.class, JdbcType.CHAR, new StringTypeHandler());
    register(String.class, JdbcType.CLOB, new ClobTypeHandler());
    register(String.class, JdbcType.VARCHAR, new StringTypeHandler());
    register(String.class, JdbcType.LONGVARCHAR, new ClobTypeHandler());
    register(String.class, JdbcType.NVARCHAR, new NStringTypeHandler());
    register(String.class, JdbcType.NCHAR, new NStringTypeHandler());
    register(String.class, JdbcType.NCLOB, new NClobTypeHandler());
    register(JdbcType.CHAR, new StringTypeHandler());
    register(JdbcType.VARCHAR, new StringTypeHandler());
    register(JdbcType.CLOB, new ClobTypeHandler());
    register(JdbcType.LONGVARCHAR, new ClobTypeHandler());
    register(JdbcType.NVARCHAR, new NStringTypeHandler());
    register(JdbcType.NCHAR, new NStringTypeHandler());
    register(JdbcType.NCLOB, new NClobTypeHandler());

    register(Object.class, JdbcType.ARRAY, new ArrayTypeHandler());
    register(JdbcType.ARRAY, new ArrayTypeHandler());

    register(BigInteger.class, new BigIntegerTypeHandler());
    register(JdbcType.BIGINT, new LongTypeHandler());

    register(BigDecimal.class, new BigDecimalTypeHandler());
    register(JdbcType.REAL, new BigDecimalTypeHandler());
    register(JdbcType.DECIMAL, new BigDecimalTypeHandler());
    register(JdbcType.NUMERIC, new BigDecimalTypeHandler());

    register(Byte[].class, new ByteObjectArrayTypeHandler());
    register(Byte[].class, JdbcType.BLOB, new BlobByteObjectArrayTypeHandler());
    register(Byte[].class, JdbcType.LONGVARBINARY, new BlobByteObjectArrayTypeHandler());
    register(byte[].class, new ByteArrayTypeHandler());
    register(byte[].class, JdbcType.BLOB, new BlobTypeHandler());
    register(byte[].class, JdbcType.LONGVARBINARY, new BlobTypeHandler());
    register(JdbcType.LONGVARBINARY, new BlobTypeHandler());
    register(JdbcType.BLOB, new BlobTypeHandler());

    register(Object.class, UNKNOWN_TYPE_HANDLER);
    register(Object.class, JdbcType.OTHER, UNKNOWN_TYPE_HANDLER);
    register(JdbcType.OTHER, UNKNOWN_TYPE_HANDLER);

    register(Date.class, new DateTypeHandler());
    register(Date.class, JdbcType.DATE, new DateOnlyTypeHandler());
    register(Date.class, JdbcType.TIME, new TimeOnlyTypeHandler());
    register(JdbcType.TIMESTAMP, new DateTypeHandler());
    register(JdbcType.DATE, new DateOnlyTypeHandler());
    register(JdbcType.TIME, new TimeOnlyTypeHandler());

    register(java.sql.Date.class, new SqlDateTypeHandler());
    register(java.sql.Time.class, new SqlTimeTypeHandler());
    register(java.sql.Timestamp.class, new SqlTimestampTypeHandler());

    // issue #273
    register(Character.class, new CharacterTypeHandler());
    register(char.class, new CharacterTypeHandler());
  }

  public boolean hasTypeHandler(Class<?> javaType) {
    return hasTypeHandler(javaType, null);
  }

  public boolean hasTypeHandler(TypeReference<?> javaTypeReference) {
    return hasTypeHandler(javaTypeReference, null);
  }

  public boolean hasTypeHandler(Class<?> javaType, JdbcType jdbcType) {
    return javaType != null && getTypeHandler((Type) javaType, jdbcType) != null;
  }

  public boolean hasTypeHandler(TypeReference<?> javaTypeReference, JdbcType jdbcType) {
    return javaTypeReference != null && getTypeHandler(javaTypeReference, jdbcType) != null;
  }

  public TypeHandler<?> getMappingTypeHandler(Class<? extends TypeHandler<?>> handlerType) {
    return ALL_TYPE_HANDLERS_MAP.get(handlerType);
  }

  public <T> TypeHandler<T> getTypeHandler(Class<T> type) {
    return getTypeHandler((Type) type, null);
  }

  public <T> TypeHandler<T> getTypeHandler(TypeReference<T> javaTypeReference) {
    return getTypeHandler(javaTypeReference, null);
  }

  public TypeHandler<?> getTypeHandler(JdbcType jdbcType) {
    return JDBC_TYPE_HANDLER_MAP.get(jdbcType);
  }

  public <T> TypeHandler<T> getTypeHandler(Class<T> type, JdbcType jdbcType) {
    return getTypeHandler((Type) type, jdbcType);
  }

  public <T> TypeHandler<T> getTypeHandler(TypeReference<T> javaTypeReference, JdbcType jdbcType) {
    return getTypeHandler(javaTypeReference.getRawType(), jdbcType);
  }

  private <T> TypeHandler<T> getTypeHandler(Type type, JdbcType jdbcType) {
    Map<JdbcType, TypeHandler<?>> jdbcHandlerMap = TYPE_HANDLER_MAP.get(type);
    TypeHandler<?> handler = null;
    if (jdbcHandlerMap != null) {
      handler = jdbcHandlerMap.get(jdbcType);
      if (handler == null) {
        handler = jdbcHandlerMap.get(null);
      }
    }
    if (handler == null && type != null && type instanceof Class && Enum.class.isAssignableFrom((Class<?>) type)) {
      handler = new EnumTypeHandler((Class<?>) type);
    }
    @SuppressWarnings("unchecked")
    // type drives generics here
    TypeHandler<T> returned = (TypeHandler<T>) handler;
    return returned;
  }

  public TypeHandler<Object> getUnknownTypeHandler() {
    return UNKNOWN_TYPE_HANDLER;
  }

  public void register(JdbcType jdbcType, TypeHandler<?> handler) {
    JDBC_TYPE_HANDLER_MAP.put(jdbcType, handler);
  }

  //
  // REGISTER INSTANCE
  //

  /**
   * 只配置了typeHandler, 没有配置jdbcType 或者javaType
   */
  @SuppressWarnings("unchecked")
  public <T> void register(TypeHandler<T> typeHandler) {
    boolean mappedTypeFound = false;
    //在自定义typeHandler的时候,可以加上注解MappedTypes 去指定关联的javaType
    //因此,此处需要扫描MappedTypes注解
    MappedTypes mappedTypes = typeHandler.getClass().getAnnotation(MappedTypes.class);
    if (mappedTypes != null) {
      for (Class<?> handledType : mappedTypes.value()) {
        register(handledType, typeHandler);
        mappedTypeFound = true;
      }
    }
    // @since 3.1.0 - try to auto-discover the mapped type
    if (!mappedTypeFound && typeHandler instanceof TypeReference) {
      try {
        TypeReference<T> typeReference = (TypeReference<T>) typeHandler;
        register(typeReference.getRawType(), typeHandler);
        mappedTypeFound = true;
      } catch (Throwable t) {
        // maybe users define the TypeReference with a different type and are not assignable, so just ignore it
      }
    }
    if (!mappedTypeFound) {
      register((Class<T>) null, typeHandler);
    }
  }

  /**
   * 配置了typeHandlerhe和javaType
   */
  public <T> void register(Class<T> javaType, TypeHandler<? extends T> typeHandler) {
    register((Type) javaType, typeHandler);
  }

  private <T> void register(Type javaType, TypeHandler<? extends T> typeHandler) {
    //扫描注解MappedJdbcTypes
    MappedJdbcTypes mappedJdbcTypes = typeHandler.getClass().getAnnotation(MappedJdbcTypes.class);
    if (mappedJdbcTypes != null) {
      for (JdbcType handledJdbcType : mappedJdbcTypes.value()) {
        register(javaType, handledJdbcType, typeHandler);
      }
      if (mappedJdbcTypes.includeNullJdbcType()) {
        register(javaType, null, typeHandler);
      }
    } else {
      register(javaType, null, typeHandler);
    }
  }

  public <T> void register(TypeReference<T> javaTypeReference, TypeHandler<? extends T> handler) {
    register(javaTypeReference.getRawType(), handler);
  }

  /**
   * typeHandlerhe、javaType、jdbcType都配置了
   */
  public <T> void register(Class<T> type, JdbcType jdbcType, TypeHandler<? extends T> handler) {
    register((Type) type, jdbcType, handler);
  }

  /**
   * 注册typeHandler的核心方法
   * 就是向Map新增数据而已
   */
  private void register(Type javaType, JdbcType jdbcType, TypeHandler<?> handler) {
    if (javaType != null) {
      Map<JdbcType, TypeHandler<?>> map = TYPE_HANDLER_MAP.get(javaType);
      if (map == null) {
        map = new HashMap<JdbcType, TypeHandler<?>>();
        TYPE_HANDLER_MAP.put(javaType, map);
      }
      map.put(jdbcType, handler);
      if (reversePrimitiveMap.containsKey(javaType)) {
        register(reversePrimitiveMap.get(javaType), jdbcType, handler);
      }
    }
    ALL_TYPE_HANDLERS_MAP.put(handler.getClass(), handler);
  }

  //
  // REGISTER CLASS
  //

  // Only handler type

  public void register(Class<?> typeHandlerClass) {
    boolean mappedTypeFound = false;
    MappedTypes mappedTypes = typeHandlerClass.getAnnotation(MappedTypes.class);
    if (mappedTypes != null) {
      for (Class<?> javaTypeClass : mappedTypes.value()) {
        register(javaTypeClass, typeHandlerClass);
        mappedTypeFound = true;
      }
    }
    if (!mappedTypeFound) {
      register(getInstance(null, typeHandlerClass));
    }
  }

  // java type + handler type

  public void register(Class<?> javaTypeClass, Class<?> typeHandlerClass) {
    register(javaTypeClass, getInstance(javaTypeClass, typeHandlerClass));
  }

  // java type + jdbc type + handler type

  public void register(Class<?> javaTypeClass, JdbcType jdbcType, Class<?> typeHandlerClass) {
    register(javaTypeClass, jdbcType, getInstance(javaTypeClass, typeHandlerClass));
  }

  // Construct a handler (used also from Builders)

  @SuppressWarnings("unchecked")
  public <T> TypeHandler<T> getInstance(Class<?> javaTypeClass, Class<?> typeHandlerClass) {
    if (javaTypeClass != null) {
      try {
        Constructor<?> c = typeHandlerClass.getConstructor(Class.class);
        return (TypeHandler<T>) c.newInstance(javaTypeClass);
      } catch (NoSuchMethodException ignored) {
        // ignored
      } catch (Exception e) {
        throw new TypeException("Failed invoking constructor for handler " + typeHandlerClass, e);
      }
    }
    try {
      Constructor<?> c = typeHandlerClass.getConstructor();
      return (TypeHandler<T>) c.newInstance();
    } catch (Exception e) {
      throw new TypeException("Unable to find a usable constructor for " + typeHandlerClass, e);
    }
  }


  /**
   * 根据指定的pacakge去扫描自定义的typeHander,然后注册
   */
  public void register(String packageName) {
    ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
    resolverUtil.find(new ResolverUtil.IsA(TypeHandler.class), packageName);
    Set<Class<? extends Class<?>>> handlerSet = resolverUtil.getClasses();
    for (Class<?> type : handlerSet) {
      //Ignore inner classes and interfaces (including package-info.java) and abstract classes
      if (!type.isAnonymousClass() && !type.isInterface() && !Modifier.isAbstract(type.getModifiers())) {
        register(type);
      }
    }
  }

  // get information

  /**
   * 通过configuration对象可以获取已注册的所有typeHandler
   */
  public Collection<TypeHandler<?>> getTypeHandlers() {
    return Collections.unmodifiableCollection(ALL_TYPE_HANDLERS_MAP.values());
  }

}
由源码可以看到, mybatis为我们实现了那么多TypeHandler, 随便打开一个TypeHandler,看其源码,都可以看到,它继承自一个抽象类:BaseTypeHandler, 那么我们是不是也能通过继承BaseTypeHandler,从而实现自定义的TypeHandler ? 答案是肯定的, 那么现在下面就为大家演示一下自定义TypeHandler。
@MappedJdbcTypes(JdbcType.VARCHAR)  
//此处如果不用注解指定jdbcType, 那么,就可以在配置文件中通过"jdbcType"属性指定, 同理, javaType 也可通过 @MappedTypes指定
public class ExampleTypeHandler extends BaseTypeHandler<String> {

  @Override
  public void setNonNullParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType) throws SQLException {
    ps.setString(i, parameter);
  }

  @Override
  public String getNullableResult(ResultSet rs, String columnName) throws SQLException {
    return rs.getString(columnName);
  }

  @Override
  public String getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
    return rs.getString(columnIndex);
  }

  @Override
  public String getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
    return cs.getString(columnIndex);
  }
}
然后,就该配置我们的自定义TypeHandler了:
<configuration>
  <typeHandlers>
      <!-- 由于自定义的TypeHandler在定义时已经通过注解指定了jdbcType, 所以此处不用再配置jdbcType -->
      <typeHandler handler="ExampleTypeHandler"/>
  </typeHandlers>

  ......

</configuration>
也就是说,我们在自定义TypeHandler的时候,可以在TypeHandler通过@MappedJdbcTypes指定jdbcType, 通过 @MappedTypes 指定javaType, 如果没有使用注解指定,那么我们就需要在配置文件中配置。详细使用,请参见Mybatis类型转换介绍

2.8 元素5:objectFactory

objectFactory是干什么的? 需要配置吗? MyBatis 每次创建结果对象的新实例时,它都会使用一个对象工厂(ObjectFactory)实例来完成默认的对象工厂需要做的仅仅是实例化目标类,要么通过默认构造方法,要么在参数映射存在的时候通过参数构造方法来实例化。默认情况下,我们不需要配置,mybatis会调用默认实现的objectFactory。 除非我们要自定义ObjectFactory的实现, 那么我们才需要去手动配置。 那么怎么自定义实现ObjectFactory? 怎么配置呢?自定义ObjectFactory只需要去继承DefaultObjectFactory(是ObjectFactory接口的实现类),并重写其方法即可。具体的,本处不多说,后面再具体讲解。 写好了ObjectFactory, 仅需做如下配置:
<configuration>
    ......
    <objectFactory type="org.mybatis.example.ExampleObjectFactory">
        <property name="someProperty" value="100"/>
    </objectFactory>
    ......
</configuration>

2.9 元素6:plugins

plugin有何作用? 需要配置吗? plugins 是一个可选配置。mybatis中的plugin其实就是个interceptor, 它可以拦截Executor 、ParameterHandler 、ResultSetHandler 、StatementHandler 的部分方法,处理我们自己的逻辑。Executor就是真正执行sql语句的东西ParameterHandler 是处理我们传入参数的,还记得前面讲TypeHandler的时候提到过,mybatis默认帮我们实现了不少的typeHandler, 当我们不显示配置typeHandler的时候,mybatis会根据参数类型自动选择合适的typeHandler执行,其实就是ParameterHandler 在选择ResultSetHandler 就是处理返回结果的。 怎么自定义plugin ? 怎么配置?要自定义一个plugin, 需要去实现Interceptor接口,这儿不细说,后面实战部分会详细讲解。定义好之后,配置如下:
<configuration>
    ......
    <plugins>
      <plugin interceptor="org.mybatis.example.ExamplePlugin">
        <property name="someProperty" value="100"/>
      </plugin>
    </plugins>
    ......
</configuration>

2.10 元素7:mappers

mappers, 这下引出mybatis的核心之一了,mappers作用 ? 需要配置吗? mappers 节点下,配置我们的mapper映射文件, 所谓的mapper映射文件,就是让mybatis 用来建立数据表和javabean映射的一个桥梁。在我们实际开发中,通常一个mapper文件对应一个dao接口, 这个mapper可以看做是dao的实现。所以,mappers必须配置。
<configuration>
    ......
    <mappers>
        <!-- 第一种方式:通过resource指定 -->
        <mapper resource="com/dy/dao/userDao.xml"/>

        <!-- 第二种方式, 通过class指定接口,进而将接口与对应的xml文件形成映射关系
             不过,使用这种方式必须保证 接口与mapper文件同名(不区分大小写), 
             我这儿接口是UserDao,那么意味着mapper文件为UserDao.xml 
        <mapper class="com.dy.dao.UserDao"/>
        -->

        <!-- 第三种方式,直接指定包,自动扫描,与方法二同理 
        <package name="com.dy.dao"/>
        -->
        <!-- 第四种方式:通过url指定mapper文件位置
        <mapper url="file://........"/>
        -->
    </mappers>
    ......
</configuration>
本篇仅作简单介绍,更高级的使用以及其实现原理,会在后面的实战部分进行详细讲解。

2.11 解析方法:objectFactoryElement、pluginElement、mapperElement

以上几个节点的解析源码,与之前提到的那些节点的解析类似,故此处不再讲。 我将源码折叠, 需要的可以打开看看。
/**
 * objectFactory 节点解析
 */
private void objectFactoryElement(XNode context) throws Exception {
    if (context != null) {
      //读取type属性的值, 接下来进行实例化ObjectFactory, 并set进 configuration
      //到此,简单讲一下configuration这个对象,其实它里面主要保存的都是mybatis的配置
      String type = context.getStringAttribute("type");
      //读取propertie的值, 根据需要可以配置, mybatis默认实现的objectFactory没有使用properties
      Properties properties = context.getChildrenAsProperties();

      ObjectFactory factory = (ObjectFactory) resolveClass(type).newInstance();
      factory.setProperties(properties);
      configuration.setObjectFactory(factory);
    }
 }


  /**
   * plugins 节点解析
   */
  private void pluginElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        String interceptor = child.getStringAttribute("interceptor");
        Properties properties = child.getChildrenAsProperties();
        //由此可见,我们在定义一个interceptor的时候,需要去实现Interceptor, 这儿先不具体讲,以后会详细讲解
        Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();
        interceptorInstance.setProperties(properties);
        configuration.addInterceptor(interceptorInstance);
      }
    }
  }

  /**
   * mappers 节点解析
   * 这是mybatis的核心之一,这儿先简单介绍,在接下来的文章会对它进行分析
   */
  private void mapperElement(XNode parent) throws Exception {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) {
          //如果mappers节点的子节点是package, 那么就扫描package下的文件, 注入进configuration
          String mapperPackage = child.getStringAttribute("name");
          configuration.addMappers(mapperPackage);
        } else {
          String resource = child.getStringAttribute("resource");
          String url = child.getStringAttribute("url");
          String mapperClass = child.getStringAttribute("class");
          //resource, url, class 三选一

          if (resource != null && url == null && mapperClass == null) {
            ErrorContext.instance().resource(resource);
            InputStream inputStream = Resources.getResourceAsStream(resource);
            //mapper映射文件都是通过XMLMapperBuilder解析
            XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
            mapperParser.parse();
          } else if (resource == null && url != null && mapperClass == null) {
            ErrorContext.instance().resource(url);
            InputStream inputStream = Resources.getUrlAsStream(url);
            XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
            mapperParser.parse();
          } else if (resource == null && url == null && mapperClass != null) {
            Class<?> mapperInterface = Resources.classForName(mapperClass);
            configuration.addMapper(mapperInterface);
          } else {
            throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
          }
        }
      }
    }
  }

2.12 元素8:settings

<settings> 
    <setting name="cacheEnabled" value="true"/> 
    <setting name="lazyLoadingEnabled" value="true"/> 
    <setting name="multipleResultSetsEnabled" value="true"/> 
    <setting name="useColumnLabel" value="true"/> 
    <setting name="useGeneratedKeys" value="false"/> 
    <setting name="enhancementEnabled" value="false"/> 
    <setting name="defaultExecutorType" value="SIMPLE"/> 
    <setting name="defaultStatementTimeout" value="25000"/> 
</settings>
setting节点里配置的值会直接改写Configuration对应的变量值,这些变量描述的是Mybatis的全局运行方式,如果对这些属性的含义不熟悉的话建议不要配置,使用默认值即可。下面这个表格描述了各个配置项的含义和默认值: 输入图片说明

2.13 解析方法:settingsElement

 private void settingsElement(XNode context) throws Exception {
    if (context != null) {
      Properties props = context.getChildrenAsProperties();
      // Check that all settings are known to the configuration class
      MetaClass metaConfig = MetaClass.forClass(Configuration.class);
      for (Object key : props.keySet()) {
        if (!metaConfig.hasSetter(String.valueOf(key))) {
          throw new BuilderException("The setting " + key + " is not known.  Make sure you spelled it correctly (case sensitive).");
        }
      }
      configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));
      configuration.setCacheEnabled(booleanValueOf(props.getProperty("cacheEnabled"), true));
      configuration.setProxyFactory((ProxyFactory) createInstance(props.getProperty("proxyFactory")));
      configuration.setLazyLoadingEnabled(booleanValueOf(props.getProperty("lazyLoadingEnabled"), false));
      configuration.setAggressiveLazyLoading(booleanValueOf(props.getProperty("aggressiveLazyLoading"), true));
      configuration.setMultipleResultSetsEnabled(booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true));
      configuration.setUseColumnLabel(booleanValueOf(props.getProperty("useColumnLabel"), true));
      configuration.setUseGeneratedKeys(booleanValueOf(props.getProperty("useGeneratedKeys"), false));
      configuration.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE")));
      configuration.setDefaultStatementTimeout(integerValueOf(props.getProperty("defaultStatementTimeout"), null));
      configuration.setMapUnderscoreToCamelCase(booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false));
      configuration.setSafeRowBoundsEnabled(booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false));
      configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION")));
      configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER")));
      configuration.setLazyLoadTriggerMethods(stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString"));
      configuration.setSafeResultHandlerEnabled(booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true));
      configuration.setDefaultScriptingLanguage(resolveClass(props.getProperty("defaultScriptingLanguage")));
      configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false));
      configuration.setLogPrefix(props.getProperty("logPrefix"));
      configuration.setLogImpl(resolveClass(props.getProperty("logImpl")));
      configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));
    }
  }
正文到此结束
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