RetentionPolicy.RUNTIME:注解不僅被儲存到class檔案中,jvm加載class檔案之後,仍然存在
擷取注解的常用方法:
/**
* 擷取指定類型的注解
*/
public <A extends Annotation> A getAnnotation(Class<A> annotationType);
/**
* 擷取所有注解,如果有的話
*/
public Annotation[] getAnnotations();
/**
* 擷取所有注解,忽略繼承的注解
*/
public Annotation[] getDeclaredAnnotations();
/**
* 指定注解是否存在該元素上,如果有則傳回true,否則false
*/
public boolean isAnnotationPresent(Class<? extends Annotation> annotationType);
/**
* 擷取Method中參數的所有注解
*/
public Annotation[][] getParameterAnnotations();
1. 定義注解
/**
* @author mazaiting
* @date 2018/1/16
*/
public class RuntimeAnnotation {
/**
* 适用類、接口(包括注解類型)或枚舉
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface ClassInfo {
String value();
}
/**
* 适用變量,也包括枚舉常量
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface FieldInfo {
int[] value();
}
/**
* 适用方法
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface MethodInfo {
String name() default "long";
String data();
int age() default 24;
}
}
2. 使用注解
/**
* @author mazaiting
* @date 2018/1/16
*/
@RuntimeAnnotation.ClassInfo("TestRuntimeAnnotation class")
public class TestRuntimeAnnotation {
@RuntimeAnnotation.FieldInfo(value = {1, 2})
public String fieldnfo = "FieldInfo";
@RuntimeAnnotation.FieldInfo(value = {10086})
public int i = 100;
@RuntimeAnnotation.MethodInfo(name = "mazaiting", data = "big")
public static String getMethodInfo() {
return TestRuntimeAnnotation.class.getSimpleName();
}
}
3. 解析注解
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView textView = (TextView) findViewById(R.id.textView);
/**運作時注解*/
textView.setText(parse());
}
/**
* 解析運作時注解
*/
private String parse() {
// 建立一個線程安全的字元串拼接對象
StringBuffer sb = new StringBuffer();
// 擷取類位元組碼
Class cls = TestRuntimeAnnotation.class;
// 擷取構造方法
Constructor[] constructors = cls.getConstructors();
// 擷取指定類型的注解
// 擷取ClassInfo注解
sb.append("Class注解:").append("\n");
RuntimeAnnotation.ClassInfo classInfo =
(RuntimeAnnotation.ClassInfo) cls.getAnnotation(RuntimeAnnotation.ClassInfo.class);
if (null != classInfo) {
// 拼接通路修飾符和類名
sb.append(Modifier.toString(cls.getModifiers())).append(" ")
.append(cls.getSimpleName()).append("\n");
sb.append("注解值:").append(classInfo.value()).append("\n\n");
}
// 擷取FieldInfo注解
Field[] fields = cls.getDeclaredFields();
for (Field field : fields) {
RuntimeAnnotation.FieldInfo fieldInfo = field.getAnnotation(RuntimeAnnotation.FieldInfo.class);
if (null != fieldInfo) {
// 拼接通路修飾符,類型名,字段名
sb.append(Modifier.toString(field.getModifiers())).append(" ")
.append(field.getType().getSimpleName()).append(" ")
.append(field.getName()).append("\n");
sb.append("注解值:").append(Arrays.toString(fieldInfo.value())).append("\n\n");
}
}
// 擷取MethodInfo注解
sb.append("Method注解:").append("\n");
Method[] methods = cls.getDeclaredMethods();
for (Method method: methods) {
RuntimeAnnotation.MethodInfo methodInfo = method.getAnnotation(RuntimeAnnotation.MethodInfo.class);
if (null != methodInfo) {
// 拼接通路修飾符、傳回值類型、方法名
sb.append(Modifier.toString(method.getModifiers())).append(" ")
.append(method.getReturnType().getSimpleName()).append(" ")
.append(method.getName()).append("\n");
// 注解值
sb.append("注解值:").append("\n");
sb.append("name: ").append(methodInfo.name()).append("\n");
sb.append("data: ").append(methodInfo.data()).append("\n");
sb.append("age: ").append(methodInfo.age()).append("\n");
}
}
return sb.toString();
}
}
效果圖:
效果圖.png