java自定义annotation

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).

Test.javapackage 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; }

Note
Method declarations must not have any parameters or a throws clause. Return types are restricted to primitives, String, Class, enums, annotations, and arrays of the preceding types.

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.

TesterInfo.javapackage 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 levelpublic @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.

TestExample.javapackage 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 { @Testvoid 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.

RunTest.javapackage 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 @TesterInfoif (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 @Testfor (Method method : obj.getDeclaredMethods()) { // if method is annotated with @Testif (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); }}OutputTesting... Priority :HIGHCreatedBy :mkyong.comTags :sales, testLastModified :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 1Done.

http://www.mkyong.com/java/java-custom-annotations-example/