最近更新light-dao遇到的。

需要在一个接口中增加default方法，同时需要对非default方法重写。

大概类似这样：

public interface BaseDao {

default String getName() {

return "name";

}

@Select("select * from ad")

List getAll();

}

我们重写的Handler类似这样：

public class DaoInvocationHandler implements InvocationHandler {

private Map sqlExecutorMap = new ConcurrentHashMap();

private DataSourceHolder dataSourceHolder;

public DaoInvocationHandler(DataSourceHolder dataSourceHolder) {

this.dataSourceHolder = dataSourceHolder;

}

//对应于Dao接口里的函数

//将每一个函数映射为一个SqlExecutor

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

if (!sqlExecutorMap.containsKey(method)) {

synchronized (method) {

if (!sqlExecutorMap.containsKey(method)) {

SqlExecutor sqlExecutor = new SqlExecutor.Builder(method, dataSourceHolder.getLightTemplate()).build();

sqlExecutorMap.put(method, sqlExecutor);

}

}

}

return sqlExecutorMap.get(method).execute(args);

}

}

我们需要对default方法做特殊处理，搜索了一下stackoverflow

里面提供了一种解决方式：

Object result = MethodHandles.lookup()

.in(method.getDeclaringClass())

.unreflectSpecial(method,method.getDeclaringClass())

.bindTo(target)

.invokeWithArguments();

但是在使用时，报错如下：

Caused by: java.lang.IllegalAccessException: no private access for invokespecial

又尝试了几次，发现这种方式的改进版：

Constructor constructor = MethodHandles.Lookup.class

.getDeclaredConstructor(Class.class, int.class);

constructor.setAccessible(true);

Class> declaringClass = method.getDeclaringClass();

int allModes = MethodHandles.Lookup.PUBLIC | MethodHandles.Lookup.PRIVATE | MethodHandles.Lookup.PROTECTED | MethodHandles.Lookup.PACKAGE;

return constructor.newInstance(declaringClass, allModes)

.unreflectSpecial(method, declaringClass)

.bindTo(proxy)

.invokeWithArguments(args);

通过设置constructor.setAccessible(true);来解决access权限问题。目前来看，问题基本解决。最终的invocationHandler代码如下：

public class DaoInvocationHandler implements InvocationHandler {

private Map sqlExecutorMap = new ConcurrentHashMap();

private DataSourceHolder dataSourceHolder;

public DaoInvocationHandler(DataSourceHolder dataSourceHolder) {

this.dataSourceHolder = dataSourceHolder;

}

//对应于Dao接口里的函数

//将每一个函数映射为一个SqlExecutor

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

//default方法不重写

if (method.isDefault()) {

Constructor constructor = MethodHandles.Lookup.class

.getDeclaredConstructor(Class.class, int.class);

constructor.setAccessible(true);

Class> declaringClass = method.getDeclaringClass();

int allModes = MethodHandles.Lookup.PUBLIC | MethodHandles.Lookup.PRIVATE | MethodHandles.Lookup.PROTECTED | MethodHandles.Lookup.PACKAGE;

return constructor.newInstance(declaringClass, allModes)

.unreflectSpecial(method, declaringClass)

.bindTo(proxy)

.invokeWithArguments(args);

} else if (!sqlExecutorMap.containsKey(method)) {

synchronized (method) {

if (!sqlExecutorMap.containsKey(method)) {

SqlExecutor sqlExecutor = new SqlExecutor.Builder(method, dataSourceHolder.getLightTemplate()).build();

sqlExecutorMap.put(method, sqlExecutor);

}

}

}

return sqlExecutorMap.get(method).execute(args);

}

}

虽然解决了问题，但还是觉得java 8应该在method里添加针对interface default方法的直接调用方式，这样绕一大圈的解决方式显然不够优雅。

只能期待reflect api下个版本的修改了。