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你用剑 、我用刀:hocho:,好的代码都很烧:smirk:,望你不吝出招:dash:!
在前面一篇分析了 mybatis 源码,从它为什么之后接口但是没有实现类就能执行数据库操作为入口,整个源码核心流程完全解释了一遍。对于一个3年以上的程序员来说,新知识的学习过程应该是从最开始 helloworld 到熟练使用 api 完成业务功能。下一步为了深入了解就需要阅读部分核心源码,从而在出问题后可以快速定位,迅速排查。从而减少线上事故的持续时长,提升个人影响力。但!这不是学习终点,因为无论是任何一个框架的源码,如果只是看那么就很难学习到它的实用技术。纸上得来终觉浅,唯有实战和操练。
那么,本章节我们去简单实现一个基于jdbc的demo版本Mybatis,从而更加清楚这样框架的设计。与此同时这份思想会让你可以在其他场景使用,比如给ES查询写一个EsBatis。实现了心情也好了;
扩展上一篇源码分析工程;itstack-demo-mybatis,增加 like 包,模仿 Mybatis 工程。完整规程下载,关注公众号:bugstack虫洞栈 | 回复:源码分析
itstack-demo-mybatis └── src ├── main │ ├── java │ │ └── org.itstack.demo │ │ ├── dao │ │ │ ├── ISchool.java │ │ │ └── IUserDao.java │ │ ├── like │ │ │ ├── Configuration.java │ │ │ ├── DefaultSqlSession.java │ │ │ ├── DefaultSqlSessionFactory.java │ │ │ ├── Resources.java │ │ │ ├── SqlSession.java │ │ │ ├── SqlSessionFactory.java │ │ │ ├── SqlSessionFactoryBuilder.java │ │ │ └── SqlSessionFactoryBuilder.java │ │ └── interfaces │ │ ├── School.java │ │ └── User.java │ ├── resources │ │ ├── mapper │ │ │ ├── School_Mapper.xml │ │ │ └── User_Mapper.xml │ │ ├── props │ │ │ └── jdbc.properties │ │ ├── spring │ │ │ ├── mybatis-config-datasource.xml │ │ │ └── spring-config-datasource.xml │ │ ├── logback.xml │ │ ├── mybatis-config.xml │ │ └── spring-config.xml │ └── webapp │ └── WEB-INF └── test └── java └── org.itstack.demo.test ├── ApiLikeTest.java ├── MybatisApiTest.java └── SpringApiTest.java 复制代码
关于整个 Demo 版本,并不是把所有 Mybatis 全部实现一遍,而是拨丝抽茧将最核心的内容展示给你,从使用上你会感受一模一样,但是实现类已经全部被替换,核心类包括;
ApiLikeTest.test_queryUserInfoById()
@Test public void test_queryUserInfoById() { String resource = "spring/mybatis-config-datasource.xml"; Reader reader; try { reader = Resources.getResourceAsReader(resource); SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader); SqlSession session = sqlMapper.openSession(); try { User user = session.selectOne("org.itstack.demo.dao.IUserDao.queryUserInfoById", 1L); System.out.println(JSON.toJSONString(user)); } finally { session.close(); reader.close(); } } catch (Exception e) { e.printStackTrace(); } } 复制代码
{"age":18,"createTime":1576944000000,"id":1,"name":"水水","updateTime":1576944000000} Process finished with exit code 0 复制代码
可能乍一看这测试类完全和 MybatisApiTest.java 测试的代码一模一样呀,也看不出区别。其实他们的引入的包是不一样;
MybatisApiTest.java 里面引入的包
import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; 复制代码
ApiLikeTest.java 里面引入的包
import org.itstack.demo.like.Resources; import org.itstack.demo.like.SqlSession; import org.itstack.demo.like.SqlSessionFactory; import org.itstack.demo.like.SqlSessionFactoryBuilder; 复制代码
好!接下来我们开始分析这部分核心代码。
这里我们采用 mybatis 的配置文件结构进行解析,在不破坏原有结构的情况下,最大可能的贴近源码。mybatis 单独使用的使用的时候使用了两个配置文件;数据源配置、Mapper 映射配置,如下;
mybatis-config-datasource.xml & 数据源配置
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://127.0.0.1:3306/itstack?useUnicode=true"/> <property name="username" value="root"/> <property name="password" value="123456"/> </dataSource> </environment> </environments> <mappers> <mapper resource="mapper/User_Mapper.xml"/> <mapper resource="mapper/School_Mapper.xml"/> </mappers> </configuration> 复制代码
User_Mapper.xml & Mapper 映射配置
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="org.itstack.demo.dao.IUserDao"> <select id="queryUserInfoById" parameterType="java.lang.Long" resultType="org.itstack.demo.po.User"> SELECT id, name, age, createTime, updateTime FROM user where id = #{id} </select> <select id="queryUserList" parameterType="org.itstack.demo.po.User" resultType="org.itstack.demo.po.User"> SELECT id, name, age, createTime, updateTime FROM user where age = #{age} </select> </mapper> 复制代码
这里的加载过程与 mybaits 不同,我们采用 dom4j 方式。在案例中会看到最开始获取资源,如下;
ApiLikeTest.test_queryUserInfoById() & 部分截取
String resource = "spring/mybatis-config-datasource.xml"; Reader reader; try { reader = Resources.getResourceAsReader(resource); ... 复制代码
从上可以看到这是通过配置文件地址获取到了读取流的过程,从而为后面解析做基础。首先我们先看 Resources 类,整个是我们的资源类。
Resources.java & 资源类
/** * 公众号 | bugstack虫洞栈 * 博 客 | https://bugstack.cn * Create by 小傅哥 @2020 */ public class Resources { public static Reader getResourceAsReader(String resource) throws IOException { return new InputStreamReader(getResourceAsStream(resource)); } private static InputStream getResourceAsStream(String resource) throws IOException { ClassLoader[] classLoaders = getClassLoaders(); for (ClassLoader classLoader : classLoaders) { InputStream inputStream = classLoader.getResourceAsStream(resource); if (null != inputStream) { return inputStream; } } throw new IOException("Could not find resource " + resource); } private static ClassLoader[] getClassLoaders() { return new ClassLoader[]{ ClassLoader.getSystemClassLoader(), Thread.currentThread().getContextClassLoader()}; } } 复制代码
这段代码方法的入口是getResourceAsReader,直到往下以此做了;
配置文件加载后开始进行解析操作,这里我们也仿照 mybatis 但进行简化,如下;
SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader); 复制代码
SqlSessionFactoryBuilder.build() & 入口构建类
public DefaultSqlSessionFactory build(Reader reader) { SAXReader saxReader = new SAXReader(); try { Document document = saxReader.read(new InputSource(reader)); Configuration configuration = parseConfiguration(document.getRootElement()); return new DefaultSqlSessionFactory(configuration); } catch (DocumentException e) { e.printStackTrace(); } return null; } 复制代码
SqlSessionFactoryBuilder.parseConfiguration() & 解析过程
private Configuration parseConfiguration(Element root) { Configuration configuration = new Configuration(); configuration.setDataSource(dataSource(root.selectNodes("//dataSource"))); configuration.setConnection(connection(configuration.dataSource)); configuration.setMapperElement(mapperElement(root.selectNodes("mappers"))); return configuration; } 复制代码
SqlSessionFactoryBuilder.dataSource() & 解析出数据源
private Map<String, String> dataSource(List<Element> list) { Map<String, String> dataSource = new HashMap<>(4); Element element = list.get(0); List content = element.content(); for (Object o : content) { Element e = (Element) o; String name = e.attributeValue("name"); String value = e.attributeValue("value"); dataSource.put(name, value); } return dataSource; } 复制代码
SqlSessionFactoryBuilder.connection() & 获取数据库连接
private Connection connection(Map<String, String> dataSource) { try { Class.forName(dataSource.get("driver")); return DriverManager.getConnection(dataSource.get("url"), dataSource.get("username"), dataSource.get("password")); } catch (ClassNotFoundException | SQLException e) { e.printStackTrace(); } return null; } 复制代码
SqlSessionFactoryBuilder.mapperElement() & 解析SQL语句
private Map<String, XNode> mapperElement(List<Element> list) { Map<String, XNode> map = new HashMap<>(); Element element = list.get(0); List content = element.content(); for (Object o : content) { Element e = (Element) o; String resource = e.attributeValue("resource"); try { Reader reader = Resources.getResourceAsReader(resource); SAXReader saxReader = new SAXReader(); Document document = saxReader.read(new InputSource(reader)); Element root = document.getRootElement(); //命名空间 String namespace = root.attributeValue("namespace"); // SELECT List<Element> selectNodes = root.selectNodes("select"); for (Element node : selectNodes) { String id = node.attributeValue("id"); String parameterType = node.attributeValue("parameterType"); String resultType = node.attributeValue("resultType"); String sql = node.getText(); // ? 匹配 Map<Integer, String> parameter = new HashMap<>(); Pattern pattern = Pattern.compile("(#//{(.*?)})"); Matcher matcher = pattern.matcher(sql); for (int i = 1; matcher.find(); i++) { String g1 = matcher.group(1); String g2 = matcher.group(2); parameter.put(i, g2); sql = sql.replace(g1, "?"); } XNode xNode = new XNode(); xNode.setNamespace(namespace); xNode.setId(id); xNode.setParameterType(parameterType); xNode.setResultType(resultType); xNode.setSql(sql); xNode.setParameter(parameter); map.put(namespace + "." + id, xNode); } } catch (Exception ex) { ex.printStackTrace(); } } return map; } 复制代码
最后将初始化后的配置类 Configuration,作为参数进行创建 DefaultSqlSessionFactory,如下;
public DefaultSqlSessionFactory build(Reader reader) { SAXReader saxReader = new SAXReader(); try { Document document = saxReader.read(new InputSource(reader)); Configuration configuration = parseConfiguration(document.getRootElement()); return new DefaultSqlSessionFactory(configuration); } catch (DocumentException e) { e.printStackTrace(); } return null; } 复制代码
DefaultSqlSessionFactory.java & SqlSessionFactory的实现类
public class DefaultSqlSessionFactory implements SqlSessionFactory { private final Configuration configuration; public DefaultSqlSessionFactory(Configuration configuration) { this.configuration = configuration; } @Override public SqlSession openSession() { return new DefaultSqlSession(configuration.connection, configuration.mapperElement); } } 复制代码
SqlSession session = sqlMapper.openSession(); 复制代码
上面这一步就是创建了DefaultSqlSession,比较简单。如下;
@Override public SqlSession openSession() { return new DefaultSqlSession(configuration.connection, configuration.mapperElement); } 复制代码
User user = session.selectOne("org.itstack.demo.dao.IUserDao.queryUserInfoById", 1L); 复制代码
在 DefaultSqlSession 中通过实现 SqlSession,提供数据库语句查询和关闭连接池,如下;
SqlSession.java & 定义
public interface SqlSession { <T> T selectOne(String statement); <T> T selectOne(String statement, Object parameter); <T> List<T> selectList(String statement); <T> List<T> selectList(String statement, Object parameter); void close(); } 复制代码
接下来看具体的执行过程,session.selectOne
DefaultSqlSession.selectOne() & 执行查询
public <T> T selectOne(String statement, Object parameter) { XNode xNode = mapperElement.get(statement); Map<Integer, String> parameterMap = xNode.getParameter(); try { PreparedStatement preparedStatement = connection.prepareStatement(xNode.getSql()); buildParameter(preparedStatement, parameter, parameterMap); ResultSet resultSet = preparedStatement.executeQuery(); List<T> objects = resultSet2Obj(resultSet, Class.forName(xNode.getResultType())); return objects.get(0); } catch (Exception e) { e.printStackTrace(); } return null; } 复制代码
selectOne 就objects.get(0);,selectList 就全部返回
通过 statement 获取最初解析 xml 时候的存储的 select 标签信息;
<select id="queryUserInfoById" parameterType="java.lang.Long" resultType="org.itstack.demo.po.User"> SELECT id, name, age, createTime, updateTime FROM user where id = #{id} </select> 复制代码
获取 sql 语句后交给 jdbc 的 PreparedStatement 类进行执行
这里还需要设置入参,我们将入参设置进行抽取,如下;
private void buildParameter(PreparedStatement preparedStatement, Object parameter, Map<Integer, String> parameterMap) throws SQLException, IllegalAccessException { int size = parameterMap.size(); // 单个参数 if (parameter instanceof Long) { for (int i = 1; i <= size; i++) { preparedStatement.setLong(i, Long.parseLong(parameter.toString())); } return; } if (parameter instanceof Integer) { for (int i = 1; i <= size; i++) { preparedStatement.setInt(i, Integer.parseInt(parameter.toString())); } return; } if (parameter instanceof String) { for (int i = 1; i <= size; i++) { preparedStatement.setString(i, parameter.toString()); } return; } Map<String, Object> fieldMap = new HashMap<>(); // 对象参数 Field[] declaredFields = parameter.getClass().getDeclaredFields(); for (Field field : declaredFields) { String name = field.getName(); field.setAccessible(true); Object obj = field.get(parameter); field.setAccessible(false); fieldMap.put(name, obj); } for (int i = 1; i <= size; i++) { String parameterDefine = parameterMap.get(i); Object obj = fieldMap.get(parameterDefine); if (obj instanceof Short) { preparedStatement.setShort(i, Short.parseShort(obj.toString())); continue; } if (obj instanceof Integer) { preparedStatement.setInt(i, Integer.parseInt(obj.toString())); continue; } if (obj instanceof Long) { preparedStatement.setLong(i, Long.parseLong(obj.toString())); continue; } if (obj instanceof String) { preparedStatement.setString(i, obj.toString()); continue; } if (obj instanceof Date) { preparedStatement.setDate(i, (java.sql.Date) obj); } } } 复制代码
设置参数后执行查询 preparedStatement.executeQuery()
接下来需要将查询结果转换为我们的类(主要是反射类的操作),resultSet2Obj(resultSet, Class.forName(xNode.getResultType()));
private <T> List<T> resultSet2Obj(ResultSet resultSet, Class<?> clazz) { List<T> list = new ArrayList<>(); try { ResultSetMetaData metaData = resultSet.getMetaData(); int columnCount = metaData.getColumnCount(); // 每次遍历行值 while (resultSet.next()) { T obj = (T) clazz.newInstance(); for (int i = 1; i <= columnCount; i++) { Object value = resultSet.getObject(i); String columnName = metaData.getColumnName(i); String setMethod = "set" + columnName.substring(0, 1).toUpperCase() + columnName.substring(1); Method method; if (value instanceof Timestamp) { method = clazz.getMethod(setMethod, Date.class); } else { method = clazz.getMethod(setMethod, value.getClass()); } method.invoke(obj, value); } list.add(obj); } } catch (Exception e) { e.printStackTrace(); } return list; } 复制代码
sql 查询有入参、有不需要入参、有查询一个、有查询集合,只需要合理包装即可,例如下面的查询集合,入参是对象类型;
ApiLikeTest.test_queryUserList()
@Test public void test_queryUserList() { String resource = "spring/mybatis-config-datasource.xml"; Reader reader; try { reader = Resources.getResourceAsReader(resource); SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader); SqlSession session = sqlMapper.openSession(); try { User req = new User(); req.setAge(18); List<User> userList = session.selectList("org.itstack.demo.dao.IUserDao.queryUserList", req); System.out.println(JSON.toJSONString(userList)); } finally { session.close(); reader.close(); } } catch (Exception e) { e.printStackTrace(); } } 复制代码
[{"age":18,"createTime":1576944000000,"id":1,"name":"水水","updateTime":1576944000000},{"age":18,"createTime":1576944000000,"id":2,"name":"豆豆","updateTime":1576944000000}] Process finished with exit code 0 复制代码