背景介绍
研究一个开源项目,做二次开发,与公司业务系统集成,基础数据打通,基础功能要做替换改造。研究代码发现,dao层操作就是一系列Mapper接口声明及MapperProvider的定义文件,以下是改造过程介绍:
关键配置
配置Sqlsession,mapper目录
DataSource dataSource = getDataSource();
TransactionFactory transactionFactory = new JdbcTransactionFactory();
Environment environment = new Environment(Constants.DEVELOPMENT, transactionFactory, dataSource);
Configuration configuration = new Configuration(environment);
configuration.setLazyLoadingEnabled(true);
//mappers包目录,据此扫描注解,动态代理生成相关mapper实现。
configuration.addMappers(ProjectMapper.class.getPackage().getName());
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
sqlSessionFactory = builder.build(configuration);
获取mapper实现类
public static <T> T getMapper(Class<T> type){
return getSqlSession().getMapper(type);
}
主要实现类
- sqlSesstionTemplate
public <T> T getMapper(Class<T> type) {
return this.getConfiguration().getMapper(type, this);
}
- Configuration
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
return this.mapperRegistry.getMapper(type, sqlSession);
}
- MapperRegistry
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory)this.knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
} else {
try {
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception var5) {
throw new BindingException("Error getting mapper instance. Cause: " + var5, var5);
}
}
}
- MapperProxyFactory
见到久违的Proxy.newProxyInstance,InvocationHandler是MapperProxy。
protected T newInstance(MapperProxy<T> mapperProxy) {
return Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[]{this.mapperInterface}, mapperProxy);
}
public T newInstance(SqlSession sqlSession) {
MapperProxy<T> mapperProxy = new MapperProxy(sqlSession, this.mapperInterface, this.methodCache);
return this.newInstance(mapperProxy);
}
- MapperProxy
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {
if (Object.class.equals(method.getDeclaringClass())) {
return method.invoke(this, args);
}
if (this.isDefaultMethod(method)) {
return this.invokeDefaultMethod(proxy, method, args);
}
} catch (Throwable var5) {
throw ExceptionUtil.unwrapThrowable(var5);
}
MapperMethod mapperMethod = this.cachedMapperMethod(method);
return mapperMethod.execute(this.sqlSession, args);
}
- MapperMethod
最终的实现是在execute方法里 执行的curd操作。
改造需求
mapper的实现基于动态代理,隐藏的很深,业务代码只有一个Mapper接口声明。
若要重新实现这个Mapper,又要尽可能减少相关代码的改造。
怎么实现呢?
总的原则:
1、不改动接口声明,只在需要改动的Mapper上添加Annotation.
2、获取mapper实现时,根据Annotation判断拦截,做自定义处理。
3、设置自定义Mapper实现为默认实现。
实现方式
- Annotation声明
/**
* 是否自定义实现mapper的标记,
* 替换默认的jdk动态代理:基于sqlSession
*
*@author WongBin
*@date 2019/10/11
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface MapperAnnotation {
/***
* mapper实现类的名称
*/
String value() default "";
Class impl();
}
- 自定义实现
@Component
@Primary
public class DatasourceMapperImpl implements DataSourceMapper {
private static Logger logger = LoggerFactory.getLogger(DatasourceMapperImpl.class);
@Override
public int insert(DataSource dataSource) {
logger.info("custom-insert:{}",dataSource);
dataSource.setId(1);
return 1;
}
....
}
- 改造mapper获取
public static <T> T getMapper(Class<T> type){
//处理自定义mapper实现类型
if(type.isAnnotationPresent(MapperAnnotation.class)){
//MapperProxyFactory.class
//MapperProxy.class
MapperAnnotation tag = type.getAnnotation(MapperAnnotation.class);
logger.info("customer-mapper:{},class:{}",tag.value(),tag.impl().getName());
return (T)Proxy.newProxyInstance(type.getClassLoader(), new Class[]{type},
(Object proxy, Method method, Object[] args) ->{
proxy = BeanContext.getBean(tag.impl());
return method.invoke(proxy,args);
});
}
//mybatis默认实现方式
return getSqlSession().getMapper(type);
}
- mapper声明改造
@MapperAnnotation(impl = DatasourceMapperImpl.class)
public interface DataSourceMapper {
达到的效果,mapper消费方无感知.接口声明无改动,达到切换实现类的目的。
- 不足的地方
mapper的实现类有两个,自定义实现加了@Primary标记。否则@Autowire引入的实现还是sqlSession动态代理生成的。
动态代理能否排除一些不需要生成的mapper呢,源码里并没有发现,尚未细究。