java自定义注解实例
In this tutorial, we will show you how to create two custom annotations – @Test and @TestInfo, to simulate a simple unit test framework.
在这篇教程中，我们将示范如何新建两个自定义的标注： @Test和@TestInfo，并模拟一个简单的单元测试框架。
P.S This unit test example is inspired by this official Java annotation article.
这个单元测试例子的灵感来自于oracle官方文章。
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).
这个@interface标识java程序，这是一份自定义标注。之后，你可以在方法级别上标注它就像这样@Test(enable=false)
Test.java
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;
}
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.
注意
方法申明必须不能带有任何参数或throws片段，返回类型限制为基本类型，字符串String，类Class，枚举eunms，标注和这些类型的数组
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应用到类级别，保存tester的详情。这个类演示返回不同的类型：enum, array and string
TesterInfo.java
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.
新建一个简单的单元测试实例，并且通过新建的标注来标注：@Test and @TesterInfo
TestExample.java
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.
下面的例子演示如何通过java反射来读取和处理自定义标注。
RunTest.java
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, <strong>test</strong> LastModified :03<strong>/</strong>01<strong>/</strong><span style="color:#000000">2014</span> <span style="color:#000000">1</span> - Test <span style="color:#ff0000">'testA'</span> - failed: java.lang.RuntimeException: This <strong>test</strong> always failed <span style="color:#000000">2</span> - Test <span style="color:#ff0000">'testC'</span> - passed <span style="color:#000000">3</span> - Test <span style="color:#ff0000">'testB'</span> - ignored Result : Total : <span style="color:#000000">3</span>, Passed: <span style="color:#000000">1</span>, Failed <span style="color:#000000">1</span>, Ignore <span style="color:#000000">1</span>
原文：http://www.mkyong.com/java/java-custom-annotations-example/
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