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自定义持久层框架

2021-06-29 00:15:39   4  举报

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AI智能生成

自定义的持久层框架

MyBatis

持久层

作者其他创作

大纲/内容

SqlSessionFactory

DefaultSqlSessionFactory

Configuration

SqlSession

DefaultSqlSession

Configuration

Executor

SimpleExecutor

自定义持久层框架实现功能的流程

InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");

InputStream resourceAsStream = Resources.class.getClassLoader().getResourceAsStream(path);

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);

// 第一：使用dom4j解析配置文件，将解析出来的内容封装到Configuration中 XMLConfigBuilder xmlConfigBuilder = new XMLConfigBuilder(); Configuration configuration = xmlConfigBuilder.parseConfig(in);

// 第二：创建sqlSessionFactory对象 DefaultSqlSessionFactory defaultSqlSessionFactory = new DefaultSqlSessionFactory(configuration);

SqlSession sqlSession = sqlSessionFactory.openSession();

return new DefaultSqlSession(configuration);

IUserDao userDao = sqlSession.getMapper(IUserDao.class);

//使用jdk动态代理来为dao接口生成代理对象并返回 Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() { public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { //获取方法名，也就是id String methodName = method.getName(); //获取方法对应的类的全限定名 String className = method.getDeclaringClass().getName(); String statementId = className + "." + methodName; //获得返回值类型 Type genericReturnType = method.getGenericReturnType(); //判断是否进行了泛型类型参数化 if (genericReturnType instanceof ParameterizedType){ List<Object> objects = selectList(statementId, args); return objects; } return selectOne(statementId,args); } });

public <E> List<E> selectList(String statementid, Object... params) throws Exception { //将要去完成simpleExecutor里的query方法的调用 SimpleExecutor simpleExecutor = new SimpleExecutor(); MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid); List<Object> list = simpleExecutor.query(configuration, mappedStatement, params); return (List<E>) list; }

//1. 注册驱动，获取连接 Connection connection = configuration.getDataSource().getConnection(); //2. 获取sql语句 String sql = mappedStatement.getSql(); BoundSql boundSql = getBoundSql(sql); //3.获取预处理对象preparedStatement PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText()); //4. 设置参数获取参数的全限定名，然后获取对应的class String parameterType = mappedStatement.getParameterType(); Class<?> parameterTypeClass = getClassType(parameterType); List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList(); for (int i = 0; i < parameterMappingList.size(); i++) { Field declaredField = parameterTypeClass.getDeclaredField(parameterMappingList.get(i).getContent()); //暴力访问 declaredField.setAccessible(true); Object o = declaredField.get(params[0]); preparedStatement.setObject(i + 1, o); } //5. 执行sql ResultSet resultSet = preparedStatement.executeQuery(); //6. 封装返回结果集 String resultType = mappedStatement.getResultType(); Class<?> resultTypeClass = getResultType(resultType); ArrayList<Object> objects = new ArrayList(); while (resultSet.next()) { Object o = resultTypeClass.newInstance(); ResultSetMetaData metaData = resultSet.getMetaData(); for (int i = 1; i <= metaData.getColumnCount(); i++) { //字段名 String columnName = metaData.getColumnName(i); //字段值 Object value = resultSet.getObject(columnName); //使用内省和反射完成封装 PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass); //获取类对应参数的读写方法的对象 Method writeMethod = propertyDescriptor.getWriteMethod(); writeMethod.invoke(o, value); } objects.add(o); }

List<User> users = userDao.findAll();

Configuration

DataSource

数据源

mappedStatementMap

key：statementid，value：封装好的MappedStatement对象

MappedStatement

resultType

parameterType

sql