Mybatis的binding模块中，MapperMethod是如何实现的？

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@[TOC]聊聊Mybatis的binding模块之MapperMethod

通过MapperProxy调用MapperMethod的execute()方法，下面先看下MapperMethod的构造方法：

javapublic MapperMethod(Class mapperInterface, Method method, Configuration config) { // ...}

@[TOC]

聊聊Mybatis的binding模块之MapperMethod

通过MapperProxy来调用MapperMethod的execute()方法，

构造方法

先看一下MapperMethod的构造方法：

public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) { this.command = new SqlCommand(config, mapperInterface, method); this.method = new MethodSignature(config, mapperInterface, method); }

SqlCommand

SqlCommand是用来记录sql语句的唯一标识和sql语句的类型：UNKNOWN, INSERT, UPDATE, DELETE, SELECT, FLUSH

public SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) { final String methodName = method.getName(); final Class<?> declaringClass = method.getDeclaringClass(); MappedStatement ms = resolveMappedStatement(mapperInterface, methodName, declaringClass, configuration); if (ms == null) { if (method.getAnnotation(Flush.class) != null) { name = null; type = SqlCommandType.FLUSH; } else { throw new BindingException("Invalid bound statement (not found): " + mapperInterface.getName() + "." + methodName); } } else { name = ms.getId(); type = ms.getSqlCommandType(); if (type == SqlCommandType.UNKNOWN) { throw new BindingException("Unknown execution method for: " + name); } } }

获取Mapper接口对应的方法名

获取Mapper接口的类型

调用resolveMappedStatement()方法返回MappedStatement，MappedStatement是xml文件中的sql解析得到的对象，id是接口名+方法名

设置name 和type

而MapperMethod保存的是方法的一些信息

MapperMethod的执行方法

看一下MapperMethod的execute()方法：

public Object execute(SqlSession sqlSession, Object[] args) { Object result; switch (command.getType()) { case INSERT: { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.insert(command.getName(), param)); break; } case UPDATE: { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.update(command.getName(), param)); break; } case DELETE: { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.delete(command.getName(), param)); break; } case SELECT: if (method.returnsVoid() && method.hasResultHandler()) { executeWithResultHandler(sqlSession, args); result = null; } else if (method.returnsMany()) { result = executeForMany(sqlSession, args); } else if (method.returnsMap()) { result = executeForMap(sqlSession, args); } else if (method.returnsCursor()) { result = executeForCursor(sqlSession, args); } else { Object param = method.convertArgsToSqlCommandParam(args); result = sqlSession.selectOne(command.getName(), param); if (method.returnsOptional() && (result == null || !method.getReturnType().equals(result.getClass()))) { result = Optional.ofNullable(result); } } break; case FLUSH: result = sqlSession.flushStatements(); break; default: throw new BindingException("Unknown execution method for: " + command.getName()); } if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) { throw new BindingException("Mapper method '" + command.getName() + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ")."); } return result; }

根据sql语句的类型进行调用，对应INSERT、UPDATE、DELETE，逻辑都差不多，都是调用convertArgsToSqlCommandParam()方法处理参数，然后调用sqlSession来进行执行sql最后返回的结果通过rowCountResult来进行处理

对于SELECT语句，根据方法的返回类型选择不同的execute方法执行，最后都是调用SqlSession中的方法

总结

至此，mybatis的binding模块差不多分析完了，大体流程就是MapperRegistry根据不同的Mapper接口获取MapperProxyFactory的实例，然后调用newInstance()方法，利用MapperProxy代理类获取Mapper接口的动态代理对象，最终调用MapperMethod的execute()传入参数和封装的sql对象信息，执行sql语句