mybatis源码-二.DefaultSqlSession动态代理接口实例Mapper

最新推荐文章于 2024-09-01 22:42:42 发布

编程家阿笨猫

最新推荐文章于 2024-09-01 22:42:42 发布

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分类专栏： mybatis

本文链接：https://blog.youkuaiyun.com/hong0220/article/details/79889150

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本文深入剖析了MyBatis框架中Mapper接口的工作原理及其实现机制，详细介绍了从DefaultSqlSession到MapperProxyFactory创建代理对象的过程，以及MapperMethod如何执行SQL操作。

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DefaultSqlSession

@Override
    public <T> T getMapper(Class<T> type) {
        return configuration.<T>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) {
        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

public T newInstance(SqlSession sqlSession) {
        final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
        return newInstance(mapperProxy);
    }
    
    protected T newInstance(MapperProxy<T> mapperProxy) {
        // 返回代理对象
        return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[]{mapperInterface}, mapperProxy);
    }

MapperProxy

/**
     * 拦截方法被增强处理
     */
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (Object.class.equals(method.getDeclaringClass())) {
            try {
                return method.invoke(this, args);
            } catch (Throwable t) {
                throw ExceptionUtil.unwrapThrowable(t);
            }
        }
        final MapperMethod mapperMethod = cachedMapperMethod(method);
        return mapperMethod.execute(sqlSession, args);
    }
    
    private MapperMethod cachedMapperMethod(Method method) {
        MapperMethod mapperMethod = methodCache.get(method);
        if (mapperMethod == null) {
            mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
            methodCache.put(method, mapperMethod);
        }
        return mapperMethod;
    }

MapperMethod

public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {
        this.command = new SqlCommand(config, mapperInterface, method);
        this.method = new MethodSignature(config, mapperInterface, method);
    }
    
    public Object execute(SqlSession sqlSession, Object[] args) {
        Object result;
        // CRUD
        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);
                    // command.getName()类全限定名.方法名
                    // 找到sql语句，传入参数，执行，得到结果
                    result = sqlSession.selectOne(command.getName(), param);
                }
                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;
    }