mybatis--动态代理实现

SqlSession sqlSession = sqlSessionFactory.openSession();
try {
    ProductMapper productMapper = sqlSession.getMapper(ProductMapper.class);
    List<Product> productList = productMapper.selectProductList();
} finally {
    sqlSession.close();
}

//这里会拦截Mapper接口的所有方法 
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (Object.class.equals(method.getDeclaringClass())) { //如果是Object中定义的方法，直接执行。如toString(),hashCode()等
      try {
        return method.invoke(this, args);//
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);  //其他Mapper接口定义的方法交由mapperMethod来执行
    return mapperMethod.execute(sqlSession, args);
  }

 1   /**
 2    * 这个方法是对SqlSession的包装，对应insert、delete、update、select四种操作
 3    */
 4 public Object execute(SqlSession sqlSession, Object[] args) {
 5     Object result;//返回结果
 6 　　 //INSERT操作
 7     if (SqlCommandType.INSERT == command.getType()) {
 8       Object param = method.convertArgsToSqlCommandParam(args);
 9       //调用sqlSession的insert方法 
10       result = rowCountResult(sqlSession.insert(command.getName(), param));
11     } else if (SqlCommandType.UPDATE == command.getType()) {
12       //UPDATE操作 同上
13       Object param = method.convertArgsToSqlCommandParam(args);
14       result = rowCountResult(sqlSession.update(command.getName(), param));
15     } else if (SqlCommandType.DELETE == command.getType()) {
16       //DELETE操作 同上
17       Object param = method.convertArgsToSqlCommandParam(args);
18       result = rowCountResult(sqlSession.delete(command.getName(), param));
19     } else if (SqlCommandType.SELECT == command.getType()) {
20       //如果返回void 并且参数有resultHandler  ,则调用 void select(String statement, Object parameter, ResultHandler handler);方法  
21       if (method.returnsVoid() && method.hasResultHandler()) {
22         executeWithResultHandler(sqlSession, args);
23         result = null;
24       } else if (method.returnsMany()) {
25         //如果返回多行结果,executeForMany这个方法调用 <E> List<E> selectList(String statement, Object parameter);   
26         result = executeForMany(sqlSession, args);
27       } else if (method.returnsMap()) {
28         //如果返回类型是MAP 则调用executeForMap方法 
29         result = executeForMap(sqlSession, args);
30       } else {
31         //否则就是查询单个对象
32         Object param = method.convertArgsToSqlCommandParam(args);
33         result = sqlSession.selectOne(command.getName(), param);
34       }
35     } else {
36         //接口方法没有和sql命令绑定
37         throw new BindingException("Unknown execution method for: " + command.getName());
38     }
39     //如果返回值为空 并且方法返回值类型是基础类型 并且不是void 则抛出异常  
40     if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
41       throw new BindingException("Mapper method ‘" + command.getName() 
42           + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
43     }
44     return result;
45   }

 1 private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {
 2     List<E> result;
 3     Object param = method.convertArgsToSqlCommandParam(args);
 4     if (method.hasRowBounds()) { //是否分页查询，RowBounds中有两个数字，offset和limit
 5       RowBounds rowBounds = method.extractRowBounds(args);
 6       result = sqlSession.<E>selectList(command.getName(), param, rowBounds);
 7     } else {
 8       result = sqlSession.<E>selectList(command.getName(), param);
 9     }
10     // issue #510 Collections & arrays support
11     if (!method.getReturnType().isAssignableFrom(result.getClass())) {
12       if (method.getReturnType().isArray()) {
13         return convertToArray(result);
14       } else {
15         return convertToDeclaredCollection(sqlSession.getConfiguration(), result);
16       }
17     }
18     return result;
19   }

  public <E> List<E> selectList(String statement) {
    return this.selectList(statement, null);
  }

  public <E> List<E> selectList(String statement, Object parameter) {
    return this.selectList(statement, parameter, RowBounds.DEFAULT);
  }

  public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
    try {
      MappedStatement ms = configuration.getMappedStatement(statement);
      List<E> result = executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
      return result;
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

private final SqlCommand command;

 1 //org.apache.ibatis.binding.MapperMethod
 2   public static class SqlCommand {
 3 
 4     private final String name;
 5     private final SqlCommandType type;
 6 
 7     public SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) {
 8       String statementName = mapperInterface.getName() + "." + method.getName();　　//获取接口+方法名
 9       MappedStatement ms = null;　　//定义一个MappedStatement，这个MapperedStatement稍后介绍
10       if (configuration.hasStatement(statementName)) {　　//从Configuration对象查找是否有这个方法的全限定名称
11         ms = configuration.getMappedStatement(statementName);　　//有，则根据方法的全限定名称获取MappedStatement实例
12       } else if (!mapperInterface.equals(method.getDeclaringClass())) { //如果没有在Configuration对象中找到这个方法，则向上父类中获取全限定方法名
13         String parentStatementName = method.getDeclaringClass().getName() + "." + method.getName();
14         if (configuration.hasStatement(parentStatementName)) {　　//在向上的父类查找是否有这个全限定方法名
15           ms = configuration.getMappedStatement(parentStatementName);　　　//有，则根据方法的全限定名称获取MappedStatement实例
16         }
17       }
18       if (ms == null) {
19         if(method.getAnnotation(Flush.class) != null){
20           name = null;
21           type = SqlCommandType.FLUSH;
22         } else {
23           throw new BindingException("Invalid bound statement (not found): " + statementName);
24         }
25       } else {
26         name = ms.getId();　　//这个ms.getId，其实就是我们在mapper.xml配置文件中配置一条sql语句时开头的<select id="……"……，即是接口的该方法名全限定名称
27         type = ms.getSqlCommandType();　　//显然这是将sql是何种类型（insert、update、delete、select）赋给type
28         if (type == SqlCommandType.UNKNOWN) {
29           throw new BindingException("Unknown execution method for: " + name);
30         }
31       }
32     }
33 
34     public String getName() {
35       return name;
36     }
37 
38     public SqlCommandType getType() {
39       return type;
40     }
41   }

MappedStatement ms = configuration.getMappedStatement(statement);
return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);