使用guice（或Spring）将依赖项注入枚举

Question

I'm integrating a servlet application with Guice (could be Spring, I choose Guice just because I worked with it). And this application use constant-specific method extensively (thousands of enums). From service, it determine the action to call:

ActionEnum act = ActionEnum.valueof("Action from context");
act.perform();

The enum action looks like this:

public enum ActionEnum {
    ACTION1 { perform() {}},
    ACTION2 { perform() {}};
    abstract void perform();
}

Is there any way to inject something in to the enum class by Guice (or Spring)? eg:

public enum ActionEnum {
    ACTION1 {
       @Inject
       SomeClass case1ToBeUsedByAction1;

       void perform() { 
            case1ToBeUsedByAction1.doSomething();
            case2ToBeUsedByActionN.doSomething();
       }
    },
    ACTION2 { void perform() { case2ToBeUsedByActionN.doSomething(); }};
    abstract void perform();
    @Inject SomeClass case2ToBeUsedByActionN;
}

Or how do I change the current code base to enable injection?

Answer 1

You could add the class as an enum value like this:

public enum TestType {

TEST_TYPE_1("TEST-1", Test1.class), 
TEST_TYPE_2("TEST-2", Test2.class), 
TEST_TYPE_3("TEST-3", Test3.class), 
TEST_TYPE_4("TEST-4", Test4.class), 
TEST_TYPE_5("TEST-5", Test5.class);

private final String testType;
private final Class<? extends TestIF> tester;

private <T extends TestIF> TestType(String testType, Class<? extends TestIF> tester)    {       
    this.testType = testType;
    this.tester = (Class<tester.TestIF>) tester;
}

public String toString() {
    return this.testType;
}

public Class<? extends TestIF> tester() {
    return this.tester;
}

and then implement the TestIF for each class and execute the injected classes like this:

TestIF tester = Guice.createInjector().getInstance(testType.tester());    
tester.perform();

Answer 2

Instances of Java enum are created at compile-time. Whereas instance creation and management by guice is dynamically executed during runtime.

Note that an enum type cannot have a public constructor, which consolidates the fact that dynamic creation of an enum type instance during runtime would not be possible.

Or how do I change the current code base to enable injection?

-- There's nothing you can do about the issue other than use a regular class type. Guice cannot do an injection into your enum class, since the injection is possible during runtime when enum type instances would have been created already.