Java Custom Annotations Example

In this tutorial, we will show you how to create two custom annotations – @Test and @TestInfo, to simulate a simple unit test framework.

P.S This unit test example is inspired by this official Java annotation article.

1. @Test Annotation

This @interface tells Java this is a custom annotation. Later, you can annotate it on method level like this @Test(enable=false).

package com.mkyong.test.core;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD) //can use in method only.
public @interface Test {
	//should ignore this test?
	public boolean enabled() default true;

2. @TesterInfo Annotation

This @TesterInfo is applied on class level, store the tester details. This shows the different use of return types – enum, array and string.

package com.mkyong.test.core;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE) //on class level
public @interface TesterInfo {
	public enum Priority {
	   LOW, MEDIUM, HIGH
	Priority priority() default Priority.MEDIUM;
	String[] tags() default "";
	String createdBy() default "Mkyong";
	String lastModified() default "03/01/2014";

3. Unit Test Example

Create a simple unit test example, and annotated with the new custom annotations – @Test and @TesterInfo.

package com.mkyong.test;
import com.mkyong.test.core.Test;
import com.mkyong.test.core.TesterInfo;
import com.mkyong.test.core.TesterInfo.Priority;
@TesterInfo(
	priority = Priority.HIGH, 
	createdBy = "mkyong.com",  
	tags = {"sales","test" }
public class TestExample {
	@Test
	void testA() {
	  if (true)
		throw new RuntimeException("This test always failed");
	@Test(enabled = false)
	void testB() {
	  if (false)
		throw new RuntimeException("This test always passed");
	@Test(enabled = true)
	void testC() {
	  if (10 > 1) {
		// do nothing, this test always passed.

4. Java reflection – Read the Annotation

Below example show you how to use Java reflection APIs to read and process the custom annotations.

package com.mkyong.test;
import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import com.mkyong.test.core.Test;
import com.mkyong.test.core.TesterInfo;
public class RunTest {
  public static void main(String[] args) throws Exception {
	System.out.println("Testing...");
	int passed = 0, failed = 0, count = 0, ignore = 0;
	Class<TestExample> obj = TestExample.class;
	// Process @TesterInfo
	if (obj.isAnnotationPresent(TesterInfo.class)) {
		Annotation annotation = obj.getAnnotation(TesterInfo.class);
		TesterInfo testerInfo = (TesterInfo) annotation;
		System.out.printf("%nPriority :%s", testerInfo.priority());
		System.out.printf("%nCreatedBy :%s", testerInfo.createdBy());
		System.out.printf("%nTags :");
		int tagLength = testerInfo.tags().length;
		for (String tag : testerInfo.tags()) {
			if (tagLength > 1) {
				System.out.print(tag + ", ");
			} else {
				System.out.print(tag);
			tagLength--;
		System.out.printf("%nLastModified :%s%n%n", testerInfo.lastModified());
	// Process @Test
	for (Method method : obj.getDeclaredMethods()) {
		// if method is annotated with @Test
		if (method.isAnnotationPresent(Test.class)) {
			Annotation annotation = method.getAnnotation(Test.class);
			Test test = (Test) annotation;
			// if enabled = true (default)
			if (test.enabled()) {
			  try {
				method.invoke(obj.newInstance());
				System.out.printf("%s - Test '%s' - passed %n", ++count, method.getName());
				passed++;
			  } catch (Throwable ex) {
				System.out.printf("%s - Test '%s' - failed: %s %n", ++count, method.getName(), ex.getCause());
				failed++;
			} else {
				System.out.printf("%s - Test '%s' - ignored%n", ++count, method.getName());
				ignore++;
	System.out.printf("%nResult : Total : %d, Passed: %d, Failed %d, Ignore %d%n", count, passed, failed, ignore);

Output

Testing...
Priority :HIGH
CreatedBy :mkyong.com
Tags :sales, test
LastModified :03/01/2014
1 - Test 'testA' - failed: java.lang.RuntimeException: This test always failed 
2 - Test 'testC' - passed 
3 - Test 'testB' - ignored
Result : Total : 3, Passed: 1, Failed 1, Ignore 1

Done.

References

1. Wikipedia : Java annotation
2. Oracle JavaSE docs – annotations
3. ElementType JavaDoc
4. RetentionPolicy JavaDoc