1

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

SSCCE 代码：

家长班

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

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非常相似FooImpl。这里出了什么问题？另请注意，我尝试了两者@AssistedInject和@Inject这里，两者都导致错误。

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()

4

2 回答 2

6

根据 Guice 的javadoc，字段注入是在构造函数注入之后执行的。

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

于 2013-02-07T20:45:17.383 回答
3

两件事情。要在构造函数中使用注入，必须使用构造函数注入：

public class ParentClass {

    private final Foo foo;
    private final Bar bar;

    @Inject
    public ParentClass(MyFactory myFactory) {
        if(myFactory == null) System.err.println("Error: I should have injected by now!");
        this.foo = myFactory.create(new HashMap<String, Object>());
        this.bar = myFactory.create(new HashMap<String, Object>(), new HashMap<String, Object>());
    }
}

另外，由于你的工厂有两个相同类型的参数，你需要给它们命名：

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

和

public class BarImpl implements Bar {

    private final Map<String, Object> mapA;
    private final Map<String, Object> mapB;

    @AssistedInject
    public BarImpl(@Assisted("B") Map<String, Object> mapA, @Assisted("C")  Map<String, Object> mapB) {
        this.mapA = mapA;
        this.mapB =mapB;
    }
}
于 2013-02-07T20:49:15.500 回答