java - Guice AssistedInject 不会注入(inject)工厂

Question

我正在尝试使用 Guice 3.0 AssistedInject，它不会实例化工厂。

SSCCE代码:

父类

public class ParentClass() {
  @Inject private MyFactory myFactory;
  private final Foo foo;
  private final Bar bar;
  public ParentClass() {
    if(myFactory == null) System.err.println("Error: I should have injected by now!");
    foo = myFactory.create(new Map<String, Object>());
    // etc.
  }
}

工厂接口(interface)

public interface MyFactory {
  Foo create(Map<String, Object> mapA);
  Bar create(Map<String, Object> mapB, Map<String, Object> mapC);
}

模块

public class ParentModule extends AbstractModule {
  @Override
  protected void configure() {
    install(new FactoryModuleBuilder()
        .implement(Foo.class, FooImpl.class)
        .implement(Bar.class, BarImpl.class)
        .build(MyFactory.class));
  }

FooImpl

public class FooImpl implements Foo {
  private final Map<String, Object> mapA;
  @AssistedInject
  public FooImpl(@Assisted Map<String, Object> mapA) {
    this.mapA = mapA;
  }
}

BarImpl 与 FooImpl 非常相似。这里出了什么问题？另请注意，我在这里尝试了 @AssistedInject 和 @Inject，两者都会导致错误。

输出:

Error: I should have injected by now!
Exception in thread "main" com.google.inject.ProvisionException: Guice provision errors:

1) Error injecting constructor, java.lang.NullPointerException
  at ParentClass.<init>(ParentClass.java:7)
  while locating com.my.package.ParentClass

1 error
        at com.google.inject.internal.InjectorImpl$4.get(InjectorImpl.java:987)
        at com.google.inject.internal.InjectorImpl.getInstance(InjectorImpl.java:1013)
        at com.my.package.ParentMain.main(ParentMain.java:16)
Caused by: java.lang.NullPointerException
        at com.my.package.ParentClass.<init>(ParentClass.java:9)
        at com.my.package.ParentClass$$FastClassByGuice$$d4b3063a.newInstance(<generated>)
        at com.google.inject.internal.cglib.reflect.$FastConstructor.newInstance(FastConstructor.java:40)
        ... 8 more

请注意第 9 行是第一次调用 myFactory.create()

Answer 1

根据 Guice 的 javadoc ，字段注入(inject)在构造函数注入(inject)之后执行。

我假设您的 ParentClass 实例是由 Guice 创建的。当您的 ParentClass 的构造函数被执行时，它的 myFactory 字段还没有被注入(inject)。