mybatis第九话 - 手写实现一个简单的mybatis版本

本文主要记录了基于整个Mybatis的使用以及源码分析篇总结，为了更加清晰的看懂Mybatis原理，简化源码手写实现一个简单的Mybatis版本

pom 基于springboot 2.5.6

	org.springframework.boot
	spring-boot-starter-web


	mysql
	mysql-connector-java
	8.0.18

目录
2.自动装配类 MapperAutoConfig

只贴了一个扫描和向容器注册的方法

@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
    //1.扫描mapper接口
    doScanner("com.example.demo", TMapper.class, this.configuration.getMapperInterfaceList());
    //初始化插件
    doScanner("com.example.demo", Intercepts.class, this.configuration.getPluGinInterfaceList());

    //2.扫描sql 这里方便读取存放到配置文件了
    doScannerStatement("application.yml");

    //3.将mapper接口和sql文件保存到MapperFactoryBean,然后注册到容器中去
    doRegister(registry);
}

//向容器注册
private void doRegister(BeanDefinitionRegistry registry) {
    for (Object object : this.configuration.getMapperInterfaceList()) {
        Class clazz = (Class) object;
        //beanName是mapper接口名
        BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(clazz);
        AbstractBeanDefinition beanDefinition = builder.getBeanDefinition();
        //class 替换为MapperFactoryBean类
        beanDefinition.setBeanClass(MapperFactoryBean.class);
        //参数传递
        beanDefinition.getPropertyValues().add("mapperInterface", clazz.getName());
        beanDefinition.getPropertyValues().add("configuration", this.configuration);
        //注册到容器 beanName是接口全名 beanClass替换成MapperFactoryBean
        registry.registerBeanDefinition(clazz.getName(), beanDefinition);

        log.info("add mapper for " + clazz.getName());
    }
}

//该类实现了FactoryBean 初始化原始类时会调用该类的getObject方法
@Data
public class MapperFactoryBean implements FactoryBean {

    private Class mapperInterface;
    Configuration configuration;

    public MapperFactoryBean() {

    }

    //此类为工厂bean 初始化该类时可以自己定义实例化对象 这里采用动态代理生成返回的对象 调用类为MapperProxy
    @Override
    public T getObject() throws Exception {
        return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(),
                new Class[]{mapperInterface}, new MapperProxy(mapperInterface, configuration));
    }

    @Override
    public Class getObjectType() {
        return this.mapperInterface;
    }
}

public class MapperProxy implements InvocationHandler, Serializable {

    Class mapperInterface;
    Configuration configuration;

    public MapperProxy(Class mapperInterface, Configuration configuration) {
        this.mapperInterface = mapperInterface;
        this.configuration = configuration;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        //处理sql的相关信息
        MapperMethod mapperMethod = new MapperMethod(configuration, method, this.mapperInterface);
        //真正的调用从这里开始的
        return mapperMethod.execute(args);
    }
}

public MapperMethod(Configuration configuration, Method method, Class mapperInterface) {
    this.method = method;
    this.sqlCommend = new SqlCommend();
    String statementId = mapperInterface.getName() + "." + method.getName();
    sqlCommend.setStatementId(statementId);
    sqlCommend.setResultType(method.getReturnType());
    sqlCommend.setParamType(method.getParameterTypes());
    sqlCommend.setSql(configuration.getMappedStatements().get(statementId));
	//创建代理类
    this.sqlSessionProxy = createSqlSessionProxy(configuration);
}

private SqlSession createSqlSessionProxy(Configuration configuration) {
    //代理invoke类指向SqlSessionInvocation类
    return (SqlSession) Proxy.newProxyInstance(this.getClass().getClassLoader(),
            new Class[]{SqlSession.class}, new SqlSessionInvocation(configuration, sqlCommend));
}

//根据sql类型区分 先会走SqlSessionInvocation代理类
public Object execute(Object[] args) {
    switch (sqlCommend.getType()) {
        case "SELECt":
            Class returnType = this.method.getReturnType();
            if (List.class.equals(returnType)) {
                return this.sqlSessionProxy.selectList(sqlCommend.getStatementId(), args);
            } else if (!void.class.equals(returnType)) {
                return this.sqlSessionProxy.selectOne(sqlCommend.getStatementId(), args);
            }
        case "UPDATE":
        case "INSERT":
            return this.sqlSessionProxy.update(sqlCommend.getStatementId(), args);
        case "DELETE":
            return this.sqlSessionProxy.delete(sqlCommend.getStatementId(), args);
    }
    throw new RuntimeException("sql类型异常," + sqlCommend.getType());
}

@Override
 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
     try {
         //获取一个新的sqlSession
         DefualtSqlSession sqlSession = getSqlSession();

         Object result = method.invoke(sqlSession, args);

         //做事务的提交 todo
         return result;
     } catch (Exception e) {
         //回滚之类的
         throw new RuntimeException(e);
     }

 }

 private DefualtSqlSession getSqlSession() {
     //创建执行器
     Executor executor = new baseExecutor(configuration, sqlCommend);

     //扫描插件实现
     executor = (Executor) this.pluginAll(executor);

     return new DefualtSqlSession(executor);
 }

 private Object pluginAll(Object executor) {
     //插件list
     List