mybatis 执行接口的方法

看下执行下面这行代码的时候，都发生了什么

User user = userMapper.getById(1L);

在上一篇中，获取mapper其实是以org.apache.ibatis.binding.MapperProxy为InvocationHandler创建代理对象。那么执行接口的方法的时候，也应该是执行MapperProxy的invoke方法

org.apache.ibatis.binding.MapperProxy#invoke

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
        if (Object.class.equals(method.getDeclaringClass())) {
            return method.invoke(this, args);
        } else if (isDefaultMethod(method)) {
            return invokeDefaultMethod(proxy, method, args);
        }
    } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
    }
    //封装下method成MapperMethod 
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
}

org.apache.ibatis.binding.MapperMethod#execute 根据查询的类型不同执行不同的方法，执行select的时候还要根据不同的返回值类型执行不同的方法

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;
}

org.apache.ibatis.session.defaults.DefaultSqlSession#selectOne(java.lang.String, java.lang.Object) selectOne是先selectList()，然后判断list的size是否等于1，为1的时候正常返回，大于一抛异常，小于1就返回null

public <T> T selectOne(String statement, Object parameter) {
    // Popular vote was to return null on 0 results and throw exception on too many.
    List<T> list = this.selectList(statement, parameter);
    if (list.size() == 1) {
        return list.get(0);
    } else if (list.size() > 1) {
        throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size());
    } else {
        return null;
    }
}

org.apache.ibatis.session.defaults.DefaultSqlSession#selectList(java.lang.String, java.lang.Object, org.apache.ibatis.session.RowBounds) 开始执行executor.query()方法了

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

来源：CSDN

作者：Bandeo

链接：https://blog.csdn.net/Bandeo/article/details/104326371

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MyBatis