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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