通过Java中的注释值获取枚举值

时间:2013-02-21 15:34:42

标签: java enums annotations

我正在尝试使用与枚举值相关联的注释字符串值,以获取对相关枚举值的引用。

我最终陷入困境......目前我有以下开发代码:

注释码:

public @interface MyCustomAnnotation{
    String value();
}

枚举代码:

public enum MyEnum{
    @MyCustomAnnotation("v1")
    VALUE1,
    @MyCustomAnnotation("v2")
    VALUE2,
    @MyCustomAnnotation("v3")
    VALUE3,
}

使用枚举注释:

String matchString = "v1";
MyEnum myEnumToMatch;

// First obtain all available annotation values
for(Annotation annotation : (MyEnum.class).getAnnotations()){
    // Determine whether our String to match on is an annotation value against
    // any of the enum values
    if(((MyCustomAnnotation)annotation).value() == matchString){
        // A matching annotation value has been found
        // I need to obtain a reference to the corrext Enum value based on
            // this annotation value
        for(MyEnum myEnum : MyEnum.values()){
            // Perhaps iterate the enum values and obtain the individual
                    // annotation value - if this matches then assign this as the
                    // value.
            // I can't find a way to do this - any ideas?
            myEnumToMatch = ??
        }
    }
}

提前致谢。

3 个答案:

答案 0 :(得分:4)

在枚举中有一个字段会更容易,如下所示:

public enum MyEnum {
    VALUE1("v1"),
    VALUE2("v2"),
    VALUE3("v3");

    private String displayValue;

    private MyEnum(string s) {
        this.displayValue = s;
    }

    public String getDisplayValue() {
        return displayValue;
    }
}

然后在你的匹配循环中,你只需遍历MyEnum.values()并寻找具有正确displayValue的那个。

答案 1 :(得分:2)

我完全同意@MichaelMyers的说法,最好在枚举中添加一个值,而不是使用注释。但是,下面的代码可以帮助您了解注释如何附加到枚举值。

@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnno {
    String value();
}

public enum Example {
    @MyAnno("v1")   FOO, 
    @MyAnno("v2")   BAR, 
    @MyAnno("v3")   BAZ
}


public static void main(String[] argv)
throws Exception {
    for (Field field : Example.class.getDeclaredFields()) {
        System.out.println(field.getName());
        for (Annotation anno : field.getAnnotations()) {
            if (anno instanceof MyAnno) {
                MyAnno myAnno = (MyAnno)anno;
                System.out.println("   anno = " + myAnno.value());
            }
        }
    }
}

答案 2 :(得分:1)

枚举常量是enum类的常规字段,因此您必须通过反射访问它们:

for (Field enumValue : MyEnum.class.getDeclaredFields()) {
    MyAnnotation annotation = enumValue.getAnnotation(MyAnnotation.class);
    if (annotation != null) {
        System.out.printf("Field '%s' is annotated with @MyAnnotation with value '%s'\n",
                enumValue.getName(),
                annotation.value());
    } else {
        System.out.printf("Field '%s' is not annotated with @MyAnnotation\n", enumValue.getName());
    }
}

请注意,这还包括一个名为$VALUES的内部字段,其中包含一个包含所有枚举值的数组。您可以使用例如过滤if (enumValue.isSynthethic()) { ... }