guice：自动绑定泛型类

Question

可以自动绑定泛型类吗？考虑一下：

通用接口：

public interface IAction<T> {
     T echo(T inst);
}

长子类型：

public class LongAction implements IAction<Long> {    
    @Override
    public Long echo(Long inst) {return inst;}
}

字符串子类型：

public class StringAction implements IAction<String> {
    @Override
    public String echo(String inst) {return inst;}
}

自定义模块：公共类CustomModule扩展AbstractModule{

@Override
protected void configure() {
  //do this automagically?
  bind(new TypeLiteral<IAction<String>>() {}).to(StringAction.class);
  bind(new TypeLiteral<IAction<Long>>() {}).to(LongAction.class);
  //
}

}

主要的

// i know i can obtain the correct instance
IAction<String> is = injector.getInstance(new Key<IAction<String>>(){});

是否可以以某种方式（例如：基抽象类、反射或其他）自动绑定StringAction和LongAction类的绑定？我试过使用反射，但没有用。




Answer 1

我设法欺骗了编译器。

class CustomModule extends AbstractModule {

static class Holder<T> {
    Class<T> param;
    Class<IAction<T>> klass;

    Holder(Class<?> p, Class<IAction<T>> k) {
        param = (Class<T>) p;
        klass = k;
    }
}

// this would be similar to the result of classpath scanning
List<IAction<?>> stuff;

public <T> void bindSome(Class<T> typeParameter, Class<IAction<T>> implementation) {
    Type parameterizedType = Types.newParameterizedType(IAction.class, typeParameter);
    bind((TypeLiteral<IAction<T>>) TypeLiteral.get(parameterizedType)).to(implementation);
}

public CustomModule() {
    stuff = new ArrayList<>();
    stuff.add(new StringAction());
    stuff.add(new LongAction());
}

@Override
protected void configure() {
    for (IAction<?> act : stuff) {
        System.out.printf("Configuring %s for %s\n", act.getTypeArguments(), act.getClass());
        //the following doesn't work because the compiler cannot understand that 
        //the 1st argument T is the same T in 2nd argument Class<T>
        //bindSome(act.getTypeArguments(), act.getClass());

        //w00t? compiler is tricked?? <String> is erased, but the holder preserves proper class?
        Holder<String> holder = new Holder(act.getTypeArguments(), (Class<IAction<String>>) act.getClass());
        bindSome(holder.param, holder.klass);

        //this is what I want to avoid doing manually
        //bind(new TypeLiteral<IAction<String>>() {}).to(StringAction.class);
    }
}
}

Answer 2

如果不想显式列出实现，则必须进行某种类路径扫描。例如，Guava的ClassPath类提供了一些支持。

请注意，类路径扫描与Guice的设计理念有些背道而驰。为您编写的每个实现向模块添加一行代码真的需要这么多额外的努力吗？