大致可分为如下几个步骤
1. 动态注册bean
1.1 根据配置mapperScan, 扫描对应的包, 将对应的类解析成BeanDefinition
1.2 通过替换BeanDefinition中的BeanClass为MapperFactoryBean, (原来的BeanClass是Mapper接口) 实现了在spring生成对应的对象时, 返回的对象不是本身类型的对象，而是MapperFactoryBean重写FactoryBean接口的getObject()方法返回的代理对象。该方法getObject()已经对mapper接口进行了代理, 即后续进行自动注入时, 也是返回getObject()生成的代理对象
2. 生成对应的代理对象
2.1 在getObject()方法中, 会获取到接口的全限定名称, 然后进一步对代理方法进行封装, 调用链如下
MapperFactoryBean: public T getObject() throws Exception { return getSqlSession().getMapper(this.mapperInterface); } DefaultSqlSession: public <T> T getMapper(Class<T> type) { //configuration是mybatis的重要配置类, 在初始化的时候, 就会将mapper接口添加到configuration中 return configuration.getMapper(type, this); } Configuration: public <T> T getMapper(Class<T> type, SqlSession sqlSession) { return mapperRegistry.getMapper(type, sqlSession); } MapperRegistry: public <T> T getMapper(Class<T> type, SqlSession sqlSession) { //获取mapper代理工厂 final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type); if (mapperProxyFactory == null) { throw new BindingException("Type " + type + " is not known to the MapperRegistry."); } try { return mapperProxyFactory.newInstance(sqlSession); } catch (Exception e) { throw new BindingException("Error getting mapper instance. Cause: " + e, e); } } MapperProxyFactory: protected T newInstance(MapperProxy<T> mapperProxy) { return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy); } public T newInstance(SqlSession sqlSession) { //返回一个新代理对象 final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache); return newInstance(mapperProxy); }
2.2 在org.apache.ibatis.binding.MapperProxy#cachedInvoker中, new PlainMethodInvoker(new MapperMethod(mapperInterface, method, sqlSession.getConfiguration())), 并且将代理方法调用器缓存起来. MapperMethod该对象即是最终调用方法的对象.
3. 执行对应的方法
3.1 方法调用, 代理里最常见的方法invoke
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { try { //过滤掉object的方法 if (Object.class.equals(method.getDeclaringClass())) { return method.invoke(this, args); } else { return cachedInvoker(method).invoke(proxy, method, args, sqlSession); } } catch (Throwable t) { throw ExceptionUtil.unwrapThrowable(t); } }
3.2. org.apache.ibatis.binding.MapperProxy.PlainMethodInvoker重写的invoke方法中,判断该方法是否被调用过(是否存在于缓存), 若没有, 则创建一个PlainMethodInvoker方法调用器, 传入MapperMethod(MapperMethod是真正执行方法的对象), 并将新创建的PlainMethodInvoker存入缓存中(methodCache), 并调用该PlainMethodInvoker的invoke方法,
3.3. xml中的id和select等标签封装成了SqlCommand, 调用mapperMethod的execute, 执行对应的增删改查.
4. 结果集封装, 进行一些数据库数据对应java对象的转换
通过mybatis的封装和代理, 将mapper.xml转换成了接口的实例对象
如有谬误, 欢迎斧正
简化版如下: https://blog.csdn.net/sinat_25991865/article/details/89891581
public interface UserMapper { List<SysUser> selectAll(); }
public class MyMapperProxy<T> implements InvocationHandler { private Class<T> mapperInterface; private SqlSession sqlSession; public MyMapperProxy(Class<T> mapperInterface, SqlSession sqlSession) { this.mapperInterface = mapperInterface; this.sqlSession = sqlSession; } @Override public Object invoke(Object proxy , Method method , Object[] args) throws Throwable { //针对不同的 sql 类型，需要调用sqlSession不同的方法 //接口方法中的参数也有很多情况 ，这里只考虑没有有参数的情况 List<T> list= sqlSession.selectList( mapperInterface.getCanonicalName() + ”.” + method.getName()); //返回数据也有很多情况，这里不做处理直接返回 return list; } }
方法调用
//获取sqlSession SqlSession sqlSession = getSqlSession(); //获取 UserMapper 接口 MyMapperProxy userMapperProxy = new MyMapperProxy( UserMapper.class , sqlSession) ; UserMapper userMapper = (UserMapper) Proxy.newProxyinstance ( Thread.currentThread().getContextClassLoader(), new Class[ ] {UserMapper.class}, userMapperProxy) ; //调 用 selectAll 方 法 List<SysUser> user= userMapper.selectAll();
