Java how to check type of annotation when loading class

Question

I want to load class (which use run time annotation), and check the type of the annotation.
The annotations are related to the fields.
The class is not in the classpath and not in eclipse project
- For this issue I needed to compile the class with it's annotation classes.
I loaded the class using this link:

http://www.java2s.com/Tutorial/Java/0125__Reflection/URLclassloader.htm

After loading the class, I'm trying to get for each field it's annotations and check the annotation type:

Field[] fields = obj.getClass().getFields();
        for (Field field : fields) {
            Annotation[] ann = field.getAnnotations();
            for (Annotation annotation : ann) {
                if (annotation.equals(Example.class)) {
                    System.out.println("Example annotation");
                }
            }

        }

I expect to see the print "Example annotation" but I didnt get it.

The test.class and Example.class have the following java source code:

public class Test
{
    @Example (size = 5)
    public int x;

    @Example (size = 3)
    public int y;
}

public @interface Example
{

    int size();

}

The 2 classes where saved on different partition, and I compiled them with javac (and got 2 .class files)

I read: 1. Java - loading annotated classes But didnt get the solution.

So what Am I doing wrong ? (why cany I see "Example annotation") ? Thanks

Bryan Davis · Answer 1 · 2014-11-26T19:44:33.963

You are comparing an Annotation type to a Class type.

Try

Field[] fields = obj.getClass().getFields();
    for (Field field : fields) {
        Annotation[] ann = field.getAnnotations();
        for (Annotation annotation : ann) {
            if (annotation.class.equals(Example.class)) {
                System.out.println("Example annotation");
            }
        }

    }

Alternatively, you could use the instanceOf operator:

if (annotation instanceOf package.Example) {
     System.out.println("Example annotation");
}

Note: Not tested locally, simply from reading.

Michael Wiles · Answer 2 · 2014-11-27T10:32:28.493

Use

 if (annotation.annotationType().equals(Example.class)) {
        System.out.println("Example annotation");
 }

Update:

The following test passes:

package annotation.test;

import org.junit.Test;

import java.lang.annotation.Annotation;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;

import junit.framework.Assert;

public class AnnotationTest {

    @Test
    public void TestAnnotationType() {
        Object obj = new ClassWithAnnotation();

        List<String> fieldList = new ArrayList<String>();

        // need to use declared fields as some are private
        Field[] fields = obj.getClass().getDeclaredFields(); 
        for (Field field : fields) {
            field.setAccessible(true);
            System.out.println("processing field " + field);
            Annotation[] ann = field.getAnnotations();
            for (Annotation annotation : ann) {
                if (annotation.annotationType().equals(Example1.class)) {
                    System.out.println(field);
                    fieldList.add(field.getName());
                }
            }
        }

        Assert.assertTrue(fieldList.contains("string1"));
        Assert.assertTrue(fieldList.contains("string2"));
        Assert.assertFalse(fieldList.contains("string3"));
        Assert.assertFalse(fieldList.contains("string4"));
        Assert.assertFalse(fieldList.contains("string5"));
    }
}

class ClassWithAnnotation {

    @Example1
    private String string1;

    @Example1
    public String string2;

    @Example2
    private String string3;

    private String string4;
    private String string5;

}

@Retention(RetentionPolicy.RUNTIME)
@interface Example1 {

}

@Retention(RetentionPolicy.RUNTIME)
@interface Example2 {

}

Java how to check type of annotation when loading class

2 Answers2