动态代理，没有被代理对象

1 在mybatis Guice 事务源码解析中，可以发现SqlSessionManager中的sqlSessionProxy使用SqlSession构建的代理

    private SqlSessionManager(SqlSessionFactory sqlSessionFactory) {
        this.sqlSessionFactory = sqlSessionFactory;
        this.sqlSessionProxy = (SqlSession)Proxy.newProxyInstance(SqlSessionFactory.class.getClassLoader(), new Class[]{SqlSession.class}, new SqlSessionManager.SqlSessionInterceptor());
    }

this.sqlSessionProxy = (SqlSession)Proxy.newProxyInstance(SqlSessionFactory.class.getClassLoader(), new Class[]{SqlSession.class}, new SqlSessionManager.SqlSessionInterceptor());

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private class SqlSessionInterceptor implements InvocationHandler {
    public SqlSessionInterceptor() {
    }

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        SqlSession sqlSession = (SqlSession)SqlSessionManager.this.localSqlSession.get();
        if(sqlSession != null) {
            try {
                return method.invoke(sqlSession, args);
            } catch (Throwable var19) {
                throw ExceptionUtil.unwrapThrowable(var19);
            }
        } else {
            SqlSession autoSqlSession = SqlSessionManager.this.openSession();
            Throwable var6 = null;

            Object var8;
            try {
                try {
                    Object t = method.invoke(autoSqlSession, args);
                    autoSqlSession.commit();
                    var8 = t;
                } catch (Throwable var20) {
                    autoSqlSession.rollback();
                    throw ExceptionUtil.unwrapThrowable(var20);
                }
            } catch (Throwable var21) {
                var6 = var21;
                throw var21;
            } finally {
                if(autoSqlSession != null) {
                    if(var6 != null) {
                        try {
                            autoSqlSession.close();
                        } catch (Throwable var18) {
                            var6.addSuppressed(var18);
                        }
                    } else {
                        autoSqlSession.close();
                    }
                }

            }

            return var8;
        }
    }
}

可以看到没有维护被代理的target对象，用的时候即时生成被代理的DefaultSqlSession对象

public class ProxyFactory implements InvocationHandler {
    //维护一个目标对象
    private Object target;
    public ProxyFactory(Object target){
        this.target = target;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("开始事务jdk");
        Object returnValue = method.invoke(target, args);
        System.out.println("提交事务jdk");
        return returnValue;
    }

    //给目标对象生成代理对象
    public Object getProxyInstance(){
        return Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), this);
    }

}

public class ProxyFactoryNonTarget implements InvocationHandler {

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("开始事务jdk");
        Object returnValue = method.invoke(new UserDao(), args);
        System.out.println("提交事务jdk");
        return returnValue;
    }

    //给目标对象生成代理对象
    public Object getProxyInstance(){
        return Proxy.newProxyInstance(ProxyFactoryNonTarget.class.getClassLoader(), new Class[]{IUserDao.class}, this);
    }

}

下面的每次invoke都生成新对象

2 mybatis本身就是根据interface直接生成代理对象，没有被代理对象，因为连被代理实现类都没有

public class MapperProxyFactory<T> {
    private final Class<T> mapperInterface;
    private final Map<Method, MapperMethodInvoker> methodCache = new ConcurrentHashMap();

    public MapperProxyFactory(Class<T> mapperInterface) {
        this.mapperInterface = mapperInterface;
    }

    public Class<T> getMapperInterface() {
        return this.mapperInterface;
    }

    public Map<Method, MapperMethodInvoker> getMethodCache() {
        return this.methodCache;
    }

    protected T newInstance(MapperProxy<T> mapperProxy) {
        return Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[]{this.mapperInterface}, mapperProxy);
    }

    public T newInstance(SqlSession sqlSession) {
        MapperProxy mapperProxy = new MapperProxy(sqlSession, this.mapperInterface, this.methodCache);
        return this.newInstance(mapperProxy);
    }
}

public class MapperProxy<T> implements InvocationHandler, Serializable {
    private static final long serialVersionUID = -4724728412955527868L;
    private static final int ALLOWED_MODES = 15;
    private static final Constructor<Lookup> lookupConstructor;
    private static final Method privateLookupInMethod;
    private final SqlSession sqlSession;

整个没有被代理对象