我在 Guice 字段注入(inject)方面遇到问题。考虑遵循类的层次结构。
abstract class Base{
@Inject
protected MyService myService;
}
class A extends Base{
@Inject
private AnotherService anotherService;
}
class B extends Base{
...
}
我希望在运行时有两个不同的 MyService 实例 - 一个用于注入(inject) A 类的所有对象,另一个用于 B 类的对象。 我知道如何通过构造函数注入(inject)来实现该行为:
bind(MyService.class).annotatedWith(Names.named("forA")).to(MyServiceImpl.class).in(Singleton.class);
bind(MyService.class).annotatedWith(Names.named("forB")).to(MyServiceImpl.class).in(Singleton.class);
class A extends Base{
@Inject @Named(value = "forA")
public A(MyService service1, AnotherService service2) {
this.myService = service1;
this.anotherService = service2;
}
问题是迁移到构造函数注入(inject)会非常复杂,所以我想坚持使用字段注入(inject)。 是否可以像我想要的那样调整场注入(inject)?
最佳答案
我会使用Custom Injections来自 Guice
来实现这一点。
首先,我将创建一个注释来注释我想要根据父类(super class)类型注入(inject)的 MyService。
@BindingAnnotation
@interface MyServiceInject {
}
然后我将使用注释来注释我的 MyService 字段。
static abstract class Base {
@MyServiceInject
protected MyService myService;
}
现在我们需要一个自定义的TypeListener
,每次遇到注入(inject)点时都会调用它。
这就是我们创建它的方式。
static class ClassBasedMyServiceInjectionListener implements TypeListener {
@Override
public <I> void hear(TypeLiteral<I> typeLiteral, TypeEncounter<I> encounter) {
Class<?> clazz = typeLiteral.getRawType();
while (clazz != null) {
for (Field field : clazz.getDeclaredFields()) {
if (field.getType() == MyService.class && field.isAnnotationPresent(MyServiceInject.class)) { //if type of field is MyService and it has MyServiceInject annotation
encounter.register(new ClassBasedMyServiceInjector<>(field,
typeLiteral.getType(),
encounter.getProvider(MyServiceA.class),
encounter.getProvider(MyServiceB.class)
)
); //Now register a MemberInjector for this encounter.
}
}
clazz = clazz.getSuperclass();
}
}
}
现在我们需要如下所示的 MemberInjector。
static class ClassBasedMyServiceInjector<T> implements MembersInjector<T> {
private final Field field;
private final Type superClassType;
private final Provider<MyServiceA> myServiceAProvider;
private final Provider<MyServiceB> myServiceBProvider;
ClassBasedMyServiceInjector(Field field, Type superClassType, Provider<MyServiceA> myServiceAProvider, Provider<MyServiceB> myServiceBProvider) {
this.field = field;
this.superClassType = superClassType;
this.myServiceAProvider = myServiceAProvider;
this.myServiceBProvider = myServiceBProvider;
field.setAccessible(true);
}
public void injectMembers(T t) { //this will be called when guice wants to inject members
try {
if (superClassType == A.class) {//if super class is of type A
field.set(t, myServiceAProvider.get()); //inject MyServiceA
} else if (superClassType == B.class) { //if super class is of type B
field.set(t, myServiceBProvider.get()); //inject MyServiceB
}
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
}
}
最后,我将像这样在模块的配置方法中绑定(bind)我们的自定义 TypeListener
。
@Override
protected void configure() {
bindListener(Matchers.any(), new ClassBasedMyServiceInjectionListener());
}
希望这有帮助。
关于java - 吉斯。如何在父类的一个字段中注入(inject)不同的对象?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/60401037/