Mybatis Mapper接口工作原理实例解析

// 1. 
DataSource dataSource = BlogDataSourceFactory.getBlogDataSource();
TransactionFactory transactionFactory = new JdbcTransactionFactory();
Environment environment = new Environment("development", transactionFactory, dataSource);
Configuration configuration = new Configuration(environment);
configuration.addMapper(BlogMapper.class);// 添加Mapper接口
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
// 2. 
SqlSession session = sqlSessionFactory.openSession();
try {
 // 3. 
 BlogMapper mapper = session.getMapper(BlogMapper.class);
 // 4.
 Blog blog = mapper.selectBlog(1);
} finally {
 session.close();
}

String resource = "org/mybatis/example/mybatis-config.xml"; // xml内容就不贴了
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

 // 3. 
 BlogMapper mapper = session.getMapper(BlogMapper.class);
 // 4.
 Blog blog = mapper.selectBlog(1);

configuration.addMapper(BlogMapper.class);

 public <T> void addMapper(Class<T> type) {
  mapperRegistry.addMapper(type);
 }

public class MapperRegistry {
 private final Map<Class<?>, MapperProxyFactory<?>> knownMappers 
                         = new HashMap<Class<?>, MapperProxyFactory<?>>();
 
public <T> void addMapper(Class<T> type) {
  if (type.isInterface()) { // 只添加接口
   if (hasMapper(type)) { // 不允许重复添加
    throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
   }
   boolean loadCompleted = false;
   try {
    knownMappers.put(type, new MapperProxyFactory<T>(type)); // 注意这里
 
    MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
    parser.parse();
    loadCompleted = true;

   } finally {
    if (!loadCompleted) {
     knownMappers.remove(type);
    }
   }
  }
 }
}

BlogMapper mapper = session.getMapper(BlogMapper.class);

public class DefaultSqlSession implements SqlSession {
 private Configuration configuration; 
  @Override
 public <T> T getMapper(Class<T> type) {
  return configuration.<T>getMapper(type, this); //最后会去调用MapperRegistry.getMapper
 }
}

public class MapperRegistry {
 
private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<Class<?>, MapperProxyFactory<?>>();// Mapper 映射
 
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
  final MapperProxyFactory<T> mapperProxyFactory =
                 (MapperProxyFactory<T>) knownMappers.get(type);
  try {
   return mapperProxyFactory.newInstance(sqlSession); // 重点看这里
  } catch (Exception e) {
  }
 }
}

public class MapperProxyFactory<T> { //映射器代理工厂

 private final Class<T> mapperInterface;
 private Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<Method, MapperMethod>();

 public MapperProxyFactory(Class<T> mapperInterface) {
  this.mapperInterface = mapperInterface;
 }
 // 删除部分代码，便于阅读

 @SuppressWarnings("unchecked")
 protected T newInstance(MapperProxy<T> mapperProxy) {
  //使用了JDK自带的动态代理生成映射器代理类的对象
  return (T) Proxy.newProxyInstance(
       mapperInterface.getClassLoader(),
       new Class[] { mapperInterface }, 
       mapperProxy);
 }
 public T newInstance(SqlSession sqlSession) {
  final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
  return newInstance(mapperProxy);
 }

}

public class MapperProxy<T> implements InvocationHandler, Serializable {// 实现了InvocationHandler
 @Override
 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
  //代理以后，所有Mapper的方法调用时，都会调用这个invoke方法
  if (Object.class.equals(method.getDeclaringClass())) {
   try {
    return method.invoke(this, args); // 注意1
   } catch (Throwable t) {
    throw ExceptionUtil.unwrapThrowable(t);
   }
  }
  final MapperMethod mapperMethod = cachedMapperMethod(method); // 使用了缓存
  //执行CURD
  return mapperMethod.execute(sqlSession, args); // 注意2
 }  
}

 public Object execute(SqlSession sqlSession, Object[] args) {
  Object result;
  if (SqlCommandType.INSERT == command.getType()) {     //insert 处理，调用SqlSession的insert
   Object param = method.convertArgsToSqlCommandParam(args);
   result = rowCountResult(sqlSession.insert(command.getName(), param));
  } else if (SqlCommandType.UPDATE == command.getType()) { // update
   Object param = method.convertArgsToSqlCommandParam(args);
   result = rowCountResult(sqlSession.update(command.getName(), param));
  } else if (SqlCommandType.DELETE == command.getType()) {  // delete
   Object param = method.convertArgsToSqlCommandParam(args);
   result = rowCountResult(sqlSession.delete(command.getName(), param));
  } else if (SqlCommandType.SELECT == command.getType()) {
   // 删除部分代码 
  } else {
   throw new BindingException("Unknown execution method for: " + command.getName());
  }
   // 删除部分代码
  return result;
 }

com.sun.proxy.$Proxy17