⽆处不在的代理模式(二)--mybatis中mapper代理sqlsession

 

 我们写一个UserMapper接口，Mybatis会为该接口创建一个MapperProxy对象。

      @Test
    public void selectTest() {
        // 会话是一个级别的 ，不能跨线程
        // 缓存// 对像
        /**  
         * 基于Mapper接口代理调用
         */

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        User user = mapper.selectByid(10);//最终通过mapperProxy也会调用到sqlSession.selectone();
        // 基于会话调用
        /**
         * 基于会话直接调用
         */
        String statementID = "com.code.read.pattern.mybatis.UserMapper.selectByid";
        user = sqlSession.selectOne(statementID,10);
    }

1、MapperProxy类的创建

    1.1 MapperRegistry类

     MapperRegistry是mapper的注册类，提供了注册一个包下面的所有Mapper接口。内部维护了一个map以mapper接口类为key，value是接口类对应的代理工厂。

 private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<>();

          

   MapperRegistry其中重要的方法void addMapper(Class<T> type)方法简单的将type放进knownMappers里面。

         

public <T> void addMapper(Class<T> type) {
    if (type.isInterface()) {
      if (hasMapper(type)) {
        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;
      try {
        knownMappers.put(type, new MapperProxyFactory<>(type));//插入mapper和对应的代理工厂
        // It's important that the type is added before the parser is run
        // otherwise the binding may automatically be attempted by the
        // mapper parser. If the type is already known, it won't try.
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
        parser.parse();//解析mapper中的方法以及statement。
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }

待续--------