[英]How do I bind the Interface with Implementation for Generic Classes?
[Guice 4.0]
我想為通用類提供一個接口,並在使用Guice進行依賴項注入中使用它。 對於下面列出的代碼,我得到以下錯誤:
Exception in thread "main" com.google.inject.CreationException: Unable to create injector, see the following errors:
1) Could not find a suitable constructor in com.ulmon.fsqtransit.guicetest.Class1. Classes must have either one (and only one) constructor annotated with @Inject or a zero-argument constructor that is not private.
at com.ulmon.fsqtransit.guicetest.Class1.class(Class1.java:14)
at com.ulmon.fsqtransit.guicetest.Module.configure(Module.java:14)
-
public class Class1<T1 extends Number, T2 extends Number>
implements InterfClass1<T1, T2> {
public static final String ANNOT1 = "ANNOT1";
public static final String ANNOT2 = "ANNOT2";
private T1 t1;
private T2 t2;
// for the factory
@AssistedInject
public Class1(
@Assisted(Class1.ANNOT1) T1 t1,
@Assisted(Class1.ANNOT2) T2 t2
) {
this.t1 = t1;
this.t2 = t2;
}
public T1 getT1() {
return t1;
}
public T2 getT2() {
return t2;
}
}
public class Module extends AbstractModule {
@Override
protected void configure() {
bind(new TypeLiteral<InterfClass1<Integer, Integer>>(){})
.to(new TypeLiteral<Class1<Integer, Integer>>(){});
}
public static void main(String[] args) {
Injector inj = Guice.createInjector(new Module());
}
}
是什么導致此錯誤?
讓我們添加工廠並修改模塊(從模塊中刪除InterfClass1接口):
public interface Class1Factory<T1 extends Number, T2 extends Number> {
public Class1<T1, T2> createClass1(
@Assisted(Class1.ANNOT1) T1 t1,
@Assisted(Class1.ANNOT2) T2 t2
);
}
public class Module extends AbstractModule {
@Override
protected void configure() {
install(new FactoryModuleBuilder()
.build(new TypeLiteral<Class1Factory<Integer, Double>>(){}));
}
public static void main(String[] args) {
Injector inj = Guice.createInjector(new Module());
Class1Factory f = inj.getInstance(Key.get(new TypeLiteral<Class1Factory<Integer, Double>>(){}));
f.createClass1(10, 11.0);
}
}
它很好用!
現在讓我們合並接口:
public class Module extends AbstractModule {
@Override
protected void configure() {
bind(new TypeLiteral<InterfClass1<Integer, Double>>(){})
.to(new TypeLiteral<Class1<Integer, Double>>(){});
install(new FactoryModuleBuilder()
.build(new TypeLiteral<Class1Factory<Integer, Double>>(){}));
}
public static void main(String[] args) {
Injector inj = Guice.createInjector(new Module());
Class1Factory f = inj.getInstance(Key.get(new TypeLiteral<Class1Factory<Integer, Double>>(){}));
f.createClass1(10, 11.0);
}
}
我們得到:
1) Could not find a suitable constructor in com.ulmon.fsqtransit.guicetest.Class1. Classes must have either one (and only one) constructor annotated with @Inject or a zero-argument constructor that is not private.
at com.ulmon.fsqtransit.guicetest.Class1.class(Class1.java:15)
at com.ulmon.fsqtransit.guicetest.Module.configure(Module.java:14)
好吧,讓我們不管錯誤如何,都更改工廠:
public interface Class1Factory<T1 extends Number, T2 extends Number> {
public InterfClass1<T1, T2> createClass1(
@Assisted(Class1.ANNOT1) T1 t1,
@Assisted(Class1.ANNOT2) T2 t2
);
}
我們得到:
1) Could not find a suitable constructor in com.ulmon.fsqtransit.guicetest.Class1. Classes must have either one (and only one) constructor annotated with @Inject or a zero-argument constructor that is not private.
at com.ulmon.fsqtransit.guicetest.Class1.class(Class1.java:15)
at com.ulmon.fsqtransit.guicetest.Module.configure(Module.java:14)
2) com.ulmon.fsqtransit.guicetest.InterfClass1<java.lang.Integer, java.lang.Double> is an interface, not a concrete class. Unable to create AssistedInject factory.
while locating com.ulmon.fsqtransit.guicetest.InterfClass1<java.lang.Integer, java.lang.Double>
at com.ulmon.fsqtransit.guicetest.Class1Factory.createClass1(Class1Factory.java:1)
但是,如果刪除模塊中接口和類之間的關系,並將此關系添加到工廠的規范中,則不會出錯:
public class Module extends AbstractModule {
@Override
protected void configure() {
install(new FactoryModuleBuilder()
.implement(new TypeLiteral<InterfClass1<Integer, Double>>(){}
, new TypeLiteral<Class1<Integer, Double>>(){})
.build(new TypeLiteral<Class1Factory<Integer, Double>>(){}));
}
public static void main(String[] args) {
Injector inj = Guice.createInjector(new Module());
Class1Factory f = inj.getInstance(Key.get(new TypeLiteral<Class1Factory<Integer, Double>>(){}));
f.createClass1(10, 11.0);
}
}
工作正常!
為什么Guice有這種奇怪的行為? 為什么無論工廠如何,我都無法將接口與實現類相關聯?
我無法弄清楚您要做什么,但是在我看來,您實際上並不是在嘗試創建AssistedInject工廠,因為您尚未創建工廠接口。 在這種情況下,您根本不需要使用@Assisted
參數。 您的構造函數應如下所示(該類沒有其他更改):
@Inject
public Class1(
@Named(Class1.ANNOT1) T1 t1,
@Named(Class1.ANNOT2) T2 t2
) {
然后,在模塊中指定綁定。 您必須明確地告訴Guice要為參數以及指定的注釋注入什么:
@Override
protected void configure() {
bind(new TypeLiteral<InterfClass1<Integer, Integer>>(){})
.to(new TypeLiteral<Class1<Integer, Integer>>(){});
bind(Integer.class)
.annotatedWith(Names.named(Class1.ANNOT1))
.toInstance(5);
bind(Integer.class)
.annotatedWith(Names.named(Class1.ANNOT2))
.toInstance(15);
}
然后,我們可以這樣運行它:
public static void main(String[] args) {
Injector inj = Guice.createInjector(new Module());
InterfClass1<Integer, Integer> interf =
inj.getInstance(Key.get(new TypeLiteral<InterfClass1<Integer, Integer>>(){}));
System.out.println(interf.getClass());
System.out.println("T1: " + interf.getT1() + " T2: " + interf.getT2());
}
如您所見,在運行它時,它將注入Class
實現,並帶有指定的兩個參數:
class guice.Class1
T1: 5 T2: 15
如果你正在試圖建立一個工廠的Class1
對象,使用AssistedInject,這是因為你所指定的generit類型參數的方式顯著更加困難。 不幸的是,您不能以常規方式使用AssistedInject注入泛型工廠 ,並且這變得更加困難,因為您的Class1
實現需要T1 extends Number
,但是您的接口可以是您想要的任何T1
。 這意味着您的工廠必須將接收到的輸入參數的類型限制為Number
子類; 換句話說,您的工廠不能只創建它想要的任何InterfClass1
,它只能創建具有適當輸入參數的實例。
希望答案的前半部分是您要執行的操作。 如果不是,我們需要有關您的用例的更多信息,以便能夠回答此問題。
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