Java 如果存在参数注释，则获取参数值
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Get parameter value if parameter annotation exists
提问by user2664820
Is it possible to get the value of a parameter if an annotation is present on that parameter?
如果该参数上存在注释，是否可以获取该参数的值？
Given EJB with parameter-level annotations:
给定带有参数级注释的 EJB：
public void fooBar(@Foo String a, String b, @Foo String c) {...}
And an interceptor:
还有一个拦截器：
@AroundInvoke
public Object doIntercept(InvocationContext context) throws Exception {
// Get value of parameters that have annotation @Foo
}
采纳答案by Sotirios Delimanolis
In your doIntercept()you can retrieve the method being called from the InvocationContextand get the parameter annotations.
在您中，doIntercept()您可以从 检索被调用的方法InvocationContext并获取参数注释。
Method method = context.getMethod();
Annotation[][] annotations = method.getParameterAnnotations();
// iterate through annotations and check
Object[] parameterValues = context.getParameters();
// check if annotation exists at each index
if (annotation[0].length > 0 /* and if the annotation is the type you want */ )
// get the value of the parameter
System.out.println(parameterValues[0]);
Because the Annotation[][]returns an empty 2nd dimension array if there are no Annotations, you know which parameter positions have the annotations. You can then call InvocationContext#getParameters()to get a Object[]with the values of all the parameters passed. The size of this array and the Annotation[][]will be the same. Just return the value of the indices where there are no annotations.
因为Annotation[][]如果没有注释，则返回一个空的第二维数组，所以您知道哪些参数位置有注释。然后您可以调用InvocationContext#getParameters()获取Object[]所有传递参数的值。这个数组的大小和Annotation[][]将是一样的。只需返回没有注释的索引值。
回答by Evgeniy Dorofeev
You can try something like this
你可以试试这样的
Method m = context.getMethod();
Object[] params = context.getParameters();
Annotation[][] a = m.getParameterAnnotations();
for(int i = 0; i < a.length; i++) {
if (a[i].length > 0) {
// this param has annotation(s)
}
}
回答by franlisa
You can try something like this,I define a Param annotation named MyAnnotation and I get the Param annotation in this way. It works.
你可以尝试这样的事情，我定义了一个名为 MyAnnotation 的 Param 注释，我以这种方式获得了 Param 注释。有用。
Annotation[][] parameterAnnotations = method.getParameterAnnotations();
Class[] parameterTypes = method.getParameterTypes();
int i=0;
for(Annotation[] annotations : parameterAnnotations){
Class parameterType = parameterTypes[i++];
for(Annotation annotation : annotations){
if(annotation instanceof MyAnnotation){
MyAnnotation myAnnotation = (MyAnnotation) annotation;
System.out.println("param: " + parameterType.getName());
System.out.println("value: " + myAnnotation.value());
}
}
}
