在運行時修改類定義的注釋字符串參數想象一下有一個類：@Something(someProperty = "some value")public class Foobar {
//...}它已經編譯(我無法控制源代碼)，并且是JVM啟動時類路徑的一部分。我希望能夠在運行時將“某些值”更改為其他值，這樣以后的任何反射都將使我的新價值而不是默認的“一些值”。這個是可能的嗎？如果是，怎么做？
3 回答
倚天杖
TA貢獻1828條經驗 獲得超3個贊
/**
* Changes the annotation value for the given key of the given annotation to newValue and returns
* the previous value.
*/@SuppressWarnings("unchecked")public static Object changeAnnotationValue(Annotation annotation, String key, Object newValue){
Object handler = Proxy.getInvocationHandler(annotation);
Field f;
try {
f = handler.getClass().getDeclaredField("memberValues");
} catch (NoSuchFieldException | SecurityException e) {
throw new IllegalStateException(e);
}
f.setAccessible(true);
Map<String, Object> memberValues;
try {
memberValues = (Map<String, Object>) f.get(handler);
} catch (IllegalArgumentException | IllegalAccessException e) {
throw new IllegalStateException(e);
}
Object oldValue = memberValues.get(key);
if (oldValue == null || oldValue.getClass() != newValue.getClass()) {
throw new IllegalArgumentException();
}
memberValues.put(key,newValue);
return oldValue;}@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.TYPE)public @interface ClassAnnotation {
String value() default "";}@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.FIELD)public @interface FieldAnnotation {
String value() default "";}@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.METHOD)public @interface MethodAnnotation {
String value() default "";}@ClassAnnotation("class test")public static class TestClass{
@FieldAnnotation("field test")
public Object field;
@MethodAnnotation("method test")
public void method(){
}}public static void main(String[] args) throws Exception {
final ClassAnnotation classAnnotation = TestClass.class.getAnnotation(ClassAnnotation.class);
System.out.println("old ClassAnnotation = " + classAnnotation.value());
changeAnnotationValue(classAnnotation, "value", "another class annotation value");
System.out.println("modified ClassAnnotation = " + classAnnotation.value());
Field field = TestClass.class.getField("field");
final FieldAnnotation fieldAnnotation = field.getAnnotation(FieldAnnotation.class);
System.out.println("old FieldAnnotation = " + fieldAnnotation.value());
changeAnnotationValue(fieldAnnotation, "value", "another field annotation value");
System.out.println("modified FieldAnnotation = " + fieldAnnotation.value());
Method method = TestClass.class.getMethod("method");
final MethodAnnotation methodAnnotation = method.getAnnotation(MethodAnnotation.class);
System.out.println("old MethodAnnotation = " + methodAnnotation.value());
changeAnnotationValue(methodAnnotation, "value", "another method annotation value");
System.out.println("modified MethodAnnotation = " + methodAnnotation.value());}
嗶嗶one
TA貢獻1854條經驗 獲得超8個贊
ignoreUnknown@JsonIgnoreProperties(ignoreUnknown = true)
final List<Annotation> matchedAnnotation = Arrays.stream(SomeClass.class.getAnnotations()).filter(annotation -> annotation.annotationType().
equals(JsonIgnoreProperties.class)).collect(Collectors.toList()); final Annotation modifiedAnnotation = new JsonIgnoreProperties() {
@Override public Class<? extends Annotation> annotationType() {
return matchedAnnotation.get(0).annotationType();
} @Override public String[] value() {
return new String[0];
} @Override public boolean ignoreUnknown() {
return false;
} @Override public boolean allowGetters() {
return false;
} @Override public boolean allowSetters() {
return false;
}}; final Method method = Class.class.getDeclaredMethod("getDeclaredAnnotationMap", null);method.setAccessible(true);
final Map<Class<? extends Annotation>, Annotation> annotations = (Map<Class<? extends Annotation>, Annotation>)
method.invoke(SomeClass.class, null);annotations.put(JsonIgnoreProperties.class, modifiedAnnotation);添加回答
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