手写Mybatis框架

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分析JDBC操作问题

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问题总结

  1. 数据库连接创建、释放频繁造成系统资源浪费,从而影响系统性能。
  2. Sql语句在代码中硬编码,造成代码不易维护,实际应用中sql变化的可能较大,sql变动需要改变 java代码。
  3. 使用preparedStatement向占有位符号传参数存在硬编码,因为sql语句的where条件不一定,可能 多也可能少,修改sql还要修改代码,系统不易维护。
  4. 对结果集解析存在硬编码(查询列名),sql变化导致解析代码变化,系统不易维护,如果能将数据 库 记录封装成pojo对象解析比较方便

解决方案

  1. 使用数据库连接池初始化连接资源
  2. 将数据库连接配置、sql语句抽取到xml配置文件中, 使其满足开闭原则
  3. 使用反射、内省等底层技术,自动将实体与表进行属性与字段的自动映射

自定义框架设计思路

架构设计图

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设计思路

使用端(提供配置)

  1. 使用sqlMapperConfig.xml提供全局配置信息(数据源等)
  2. 使用Mapper.xml提供sql语句文件信息
  3. 提供SqlSession接口类实现select、insert、update、delete操作

框架端(JDBC封装)

  1. 读取配置文件
    • 读取sqlMapperconfig.xml
    • 读取Mapper.xml
  2. 解析配置文件
    • 解析文件生成Configuration、MapperStatement对象
  3. 执行JDBC流程

自定义框架实现

使用端

创建配置文件

sqlMapperConfig.xml(全局配置文件,包括数据源配置,mapper路径等)

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

<!--数据源配置-->

<datasource>

<property name="driverClass" value="com.mysql.cj.jdbc.Driver"/>

<property name="jdbcUrl" value="jdbc:mysql://localhost:3306/test"/>

<property name="username" value="root"/>

<property name="password" value=""/>

</datasource>

<!--引入mapper.xml文件路径-->

<mapper resource="mapper/userMapper.xml"/>

</configuration>
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mapper.xml(namespace命名空间、SQL语句配置等)

<?xml version="1.0" encoding="utf-8" ?>

<mapper namespace="com.gigabytc.dao.UserDao">

<select id="findAll" resultType="com.gigabytc.entity.User" >

select * from user

</select>

<select id="findByCondition" resultType="com.gigabytc.entity.User" parameterType="com.gigabytc.entity.User">

select * from user where id = #{id} and username = #{username}

</select>

<insert id="addUser" parameterType="com.gigabytc.entity.User" resultType="int">

insert into user values(#{id}, #{username}, #{password}, #{birthday})

</insert>

<update id="updateUser" parameterType="com.gigabytc.entity.User" resultType="int" >

update user SET username = #{username}, password=#{password}, birthday=#{birthday} WHERE id = #{id}

</update>

<delete id="deleteUser" parameterType="com.gigabytc.entity.User" resultType="int" >

delete from user where id=#{id}

</delete>

</mapper>
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使用sqlSession操作接口(读取配置文件构建SqlSession数据库操作)

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

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

sqlSession = sqlSessionFactory.openSession();

List<User> list = sqlSession.selectList("user.findAll");
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框架端

解析配置文件

Configuration(全局配置)

@Data
public class Configuration {

/**
- 数据源
*/
private DataSource dataSource;

/**
- SQL statement集合
*/
private Map<String, MapperStatement> mapperStatementMap = new HashMap<>();

}
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MapperStatement(SQL语句配置)

@Data
public class MapperStatement {

/**
	statement-id标识(namespace+id)
*/
private String id;

/**
- 参数类型
*/
private String parameterType;

/**
- 返回类型
*/
private String resultType;

/**
- sql语句
*/
private String sql;

/**
- sql类型
*/
private SqlType sqlType;

}
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XmlConfigBuilder(全局配置解析)

public class XMLConfigBuilder {

public Configuration parseConfiguration(InputStream inputStream) throws DocumentException, PropertyVetoException {

Configuration configuration = new Configuration();

//解析数据源配置

Document document = new SAXReader().read(inputStream);

Element rootElement = document.getRootElement();

List<Element> list = rootElement.selectNodes("//datasource/property");

Properties properties = new Properties();

for (Element element : list) {

String name = element.attributeValue("name");

String value = element.attributeValue("value");

properties.setProperty(name,value);

}

//构建连接池

ComboPooledDataSource comboPooledDataSource = new ComboPooledDataSource();

comboPooledDataSource.setDriverClass(properties.getProperty("driverClass"));

comboPooledDataSource.setJdbcUrl(properties.getProperty("jdbcUrl"));

comboPooledDataSource.setUser(properties.getProperty("username"));

comboPooledDataSource.setPassword(properties.getProperty("password"));

configuration.setDataSource(comboPooledDataSource);

//读取mapper.xml文件路径,解析mapper.xml

List<Element> mapperList = rootElement.selectNodes("//mapper");

for (Element element : mapperList) {

String resource = element.attributeValue("resource");

XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(configuration);

xmlMapperBuilder.parseMapper(Resources.getResourceAsStream(resource));

}
return configuration;
}
}
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XmlMapperStatementBuilder(SQL语句解析)

public class XMLMapperBuilder {

private Configuration configuration;

public XMLMapperBuilder(Configuration configuration) {

this.configuration = configuration;

}

public void parseMapper(InputStream inputStream) throws DocumentException {

//解析SQL statement并封装到集合

Document document = new SAXReader().read(inputStream);

Element rootElement = document.getRootElement();

//解析sql语句封装MapperStatement

buildStatement(rootElement, new String[]{"select", "update", "insert", "delete"});

}

private void parseStatement(String namespace, Element element) {

String id = element.attributeValue("id");

String parameterType = element.attributeValue("parameterType");

String resultType = element.attributeValue("resultType");

String sql = element.getTextTrim();

String elementName = element.getName();

SqlType sqlType = SqlType.valueOf(elementName.toUpperCase());

MapperStatement mapperStatement = new MapperStatement();

mapperStatement.setId(id);

mapperStatement.setParameterType(parameterType);

mapperStatement.setResultType(resultType);

mapperStatement.setSql(sql);

mapperStatement.setSqlType(sqlType);

String statementId = namespace + "." + id;

configuration.getMapperStatementMap().put(statementId, mapperStatement);

}

private void buildStatement(Element rootElement, String[] nodes) {

String namespace = rootElement.attributeValue("namespace");

for (String node : nodes) {

List<Element> list = rootElement.selectNodes("//" + node);

for (Element element : list) {

parseStatement(namespace, element);

}

}

}

}
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SqlSession相关接口实现

SqlSessionFactoryBuilder

public class SqlSessionFactoryBuilder {

public SqlSessionFactory build(InputStream inputStream) throws PropertyVetoException, DocumentException {

XMLConfigBuilder xmlConfigBuilder = new XMLConfigBuilder();

Configuration configuration = xmlConfigBuilder.parseConfiguration(inputStream);

return new DefaultSqlSessionFactory(configuration);

}

}
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DefaultSqlSessionFactory

public class DefaultSqlSessionFactory implements SqlSessionFactory{

private final Configuration configuration;

public DefaultSqlSessionFactory(Configuration configuration) {

this.configuration = configuration;

}

@Override

public SqlSession openSession() {

return new DefaultSqlSession(configuration);

}

}
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DefaultSqlSession

public class DefaultSqlSession implements SqlSession{

public DefaultSqlSession(Configuration configuration) {

this.configuration = configuration;

}

private Configuration configuration;

@Override

public <E> List<E> selectList(String statementId, Object... params) throws Exception {

Executor selectExecutor = new SelectExecutor();

MapperStatement mapperStatement = configuration.getMapperStatementMap().get(statementId);

return selectExecutor.query(configuration, mapperStatement, params);

}

@Override

public <T> T selectOne(String statementId, Object... params) throws Exception {

List<Object> objects = selectList(statementId, params);

if (objects.size() == 1) {

return (T) objects.get(0);

}else {

throw new RuntimeException("查询结果过多或不存在");

}

}

@Override

public int insert(String statementId, Object... params) throws Exception {

return this.update(statementId,params);

}

@Override

public int update(String statementId, Object... params) throws Exception {

Executor updateExecutor = new UpdateExecutor();

MapperStatement mapperStatement = configuration.getMapperStatementMap().get(statementId);

return updateExecutor.update(configuration,mapperStatement,params);

}

@Override

public int delete(String statementId, Object... params) throws Exception {

return this.update(statementId,params);

}

@Override

public <T> T getMapper(Class<?> c) {

Object o = Proxy

.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{c}, new InvocationHandler() {

@Override

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

Class<?> declaringClass = method.getDeclaringClass();

String statementId = declaringClass.getName() + "." + method.getName();

MapperStatement mapperStatement = configuration.getMapperStatementMap().get(statementId);

SqlType sqlType = mapperStatement.getSqlType();

switch (sqlType) {

case SELECT:

Type genericReturnType = method.getGenericReturnType();

// 判断是否进行了 泛型类型参数化

if(genericReturnType instanceof ParameterizedType){

return selectList(statementId, args);

}

return selectOne(statementId,args);

case INSERT:

return insert(statementId,args);

case UPDATE:

return update(statementId,args);

case DELETE:

return delete(statementId,args);

default :

break;

}

return null;

}

});

return (T) o;

}

}
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参考代码

lov3r/lagou_mybatis

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