[TOC]
public Executor newExecutor(Transaction transaction, ExecutorType executorType) { executorType = executorType == null ? defaultExecutorType : executorType; executorType = executorType == null ? ExecutorType.SIMPLE : executorType; Executor executor; if (ExecutorType.BATCH == executorType) { executor = new BatchExecutor(this, transaction); } else if (ExecutorType.REUSE == executorType) { executor = new ReuseExecutor(this, transaction); } else { executor = new SimpleExecutor(this, transaction); } if (cacheEnabled) { executor = new CachingExecutor(executor); } executor = (Executor) interceptorChain.pluginAll(executor); return executor; }
- 通过上面的代码我们可以看出来,`cacheEnabled`这个属性是控制二级缓存的配置的。而这个属性在Configuration中默认是true。这里说明了mybatis默认是开启缓存功能的。二级缓存和一级缓存的区别其实除了范围以外,他们的不同点就是顺序不同。真正开启二级缓存的是在mapper的xml中配置cache标签就行了。
SqlSession sqlSession = SqlSessionFactoryUtils.openSqlsession(); StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); Student student = mapper.getStudentByIdAndName("1", "1"); System.out.println(student); SqlSession sqlSession1 = SqlSessionFactoryUtils.sqlSessionFactory.openSession(); StudentMapper mapper1 = sqlSession1.getMapper(StudentMapper.class); Student studentByIdAndName = mapper1.getStudentByIdAndName("1", "1"); System.out.println(studentByIdAndName);
@Data @Builder @Accessors(chain = true) public class Student { /** * 学生索引id * */ * private String id; * /** * * 姓名 * */ * private String userName; /** * 用户昵称 * */ * private String userNick; /** * 年龄 * */ * private Integer age; * /** * * 性别 true : 男 ; false : 女 * */ * private SexEnum sex; * /** * * 生日 * */ * private Date birth; * /** * * 身高 * */ * private Double height; * }
CacheingExecutor.commit()
这个方法里面有事物的提交 tcm.commit()
。
SqlSession sqlSession = SqlSessionFactoryUtils.openSqlsession(); StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); Student student = mapper.getStudentByIdAndName("1", "1"); System.out.println(student); sqlSession.commit(); SqlSession sqlSession1 = SqlSessionFactoryUtils.sqlSessionFactory.openSession(); StudentMapper mapper1 = sqlSession1.getMapper(StudentMapper.class); Student studentByIdAndName = mapper1.getStudentByIdAndName("1", "1"); System.out.println(studentByIdAndName);
synchronized
@Override public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { //获取Cache对象 Cache cache = ms.getCache(); if (cache != null) { //根据statment配置刷新缓存,默认是insert、update、delete会刷新缓存 flushCacheIfRequired(ms); //二级缓存开启入口。 if (ms.isUseCache() && resultHandler == null) { //这个方法主要用来处理存储过程。后续章节说明 ensureNoOutParams(ms, boundSql); @SuppressWarnings("unchecked") //通过缓存事物查询数据 List<E> list = (List<E>) tcm.getObject(cache, key); if (list == null) { //调用委托类查询数据 list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); //加入缓存,供下次获取 tcm.putObject(cache, key, list); } return list; } } //没有开启二级缓存则继续往下走 return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); }
# 缺点 - 二级缓存因为更加广泛,所以容易造成脏数据。尤其是在关联查询的时候有序无法控制刷新力度。很容易出现脏读。
PerpetualCache
是缓存链上最基本的缓存类。我们自定义的缓存就是替代这个类的。在mybatis中会现根据我们注册进来的类进行实例化。如果没有则用默认的 PerpetualCache
这个类作为基础缓存类。