注解主要是用来减少代码的冗余,用较少的代码就可以实现更多的功能.
java提供了四类元注解,我们构建新的注解都是用元注解来实现的,下边就类注解Type,全局变量注解Filed,方法注解Method分别实现,以及对这几个注解进行解析.
注解就运行周期分为三种:Source,Class,Runtime,当前的例子都是针对Runtime来实现的.
类注解
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface TypeAnno {
String table() default "table";
}
方法注解
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@interface MethodAnno {
FiledAnnoName setAnnoName() default @FiledAnnoName;
FiledAnnoAge setAnnoAge() default @FiledAnnoAge;
String method() default "method";
}
filed注解
@Target(ElementType.FIELD)//全局变量
@Retention(RetentionPolicy.RUNTIME)//运行时注解
@interface FiledAnnoAge {
int age() default 0;//注解 构造方法无参 必须有默认值
}
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface FiledAnnoName {
String value() default "";
}
使用注解的bean
@TypeAnno
public class AnnoBean {
@FiledAnnoName("嘿嘿")
String name = "Lucy";
@FiledAnnoAge(age = 12)
int age = 20;
//value可不需要写成key=value的样式,直接写value,但是必须是value的属性.
@MethodAnno(setAnnoName = @FiledAnnoName("方法"), setAnnoAge = @FiledAnnoAge(age = 18))
public void testAnno() {
}
}
注解解析器
public class AnnoCreator {
/**
* 解析局部变量的注解
*
* @throws Exception
*/
public static void annoFiled() throws Exception {
Class<AnnoBean> clazz = AnnoBean.class;
//创建实例
AnnoBean annoBean = clazz.newInstance();
//得到类中的所有定义的属性
for (Field filed : clazz.getDeclaredFields()) {
//得到属性的注解，对一个目标可以使用多个注解
Annotation[] anns = filed.getAnnotations();//得到所有注解
if (anns.length < 1) {
continue;
}
//MyAge注解分析
if (anns[0] instanceof FiledAnnoAge) {
FiledAnnoAge filedAnnoAge = (FiledAnnoAge) anns[0];//注解的值
String name = filed.getName();
Log.e("filedName_AGE", name);
int age = filed.getInt(annoBean);//实际的值
Log.e("AGE", age + filedAnnoAge.age() + "");//实际的值+注解的值
}
//MyName注解分析
if (anns[0] instanceof FiledAnnoName) {
FiledAnnoName filedAnnoName = (FiledAnnoName) anns[0];
String name = filedAnnoName.value();
String fileName = (String) filed.get(annoBean);
String filedName = filed.getName();
Log.e("filedName_NAME", filedName);
Log.e("Name", name + fileName + "");
}
}
}
/**
* 解析类的注解
*
* @throws Exception
*/
public static void annoType() throws Exception {
Class<AnnoBean> clazz = AnnoBean.class;
TypeAnno typeAnno = clazz.getAnnotation(TypeAnno.class);//得到单个注解
Log.e("TableAnno", typeAnno.table());
}
/**
* 解析方法的注解
*
* @throws Exception
*/
public static void annoMethod() throws Exception {
Class<AnnoBean> clazz = AnnoBean.class;
//根据反射得到方法
Method[] methods = clazz.getMethods();
for (Method method:methods) {
if (method.getName().equals("testAnno")){
MethodAnno annotation = method.getAnnotation(MethodAnno.class);
FiledAnnoAge filedAnnoAge = annotation.setAnnoAge();
int age = filedAnnoAge.age();
FiledAnnoName filedAnnoName = annotation.setAnnoName();
String name = filedAnnoName.value();
Log.e("Method_ANno", age + name + annotation.method());
}
}
}
}
注解的调用测试
try {
AnnoCreator.annoFiled();
AnnoCreator.annoType();
AnnoCreator.annoMethod();
} catch (Exception e) {
Log.e("ERROR",e.toString());
}
测试结果
image.png
