使用spring已有2年之久，卻還是停留在使用階段，感覺這麼下去不是辦法，所以還是想往深處一探究竟。

今天無意中查詢到java註解，才瞭解到原來那些框架裡的註解全是基於java所提供的元註解上編寫的，也就是說，我們自己也可以自定義註解。參考資料出處：http://blog.sina.com.cn/s/blog_93dc666c0101gzn5.html

首先，新建一個自定義的註解類

<span style="font-size:18px;">import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target({ElementType.TYPE,ElementType.METHOD,ElementType.FIELD,ElementType.CONSTRUCTOR})
@Retention(RetentionPolicy.RUNTIME)
public @interface TestA {
    String name();
    int id() default 0;
    Class gid();
}</span>
 

<span style="font-size:18px;">import java.util.HashMap;
import java.util.Map;

@TestA(name="type",gid=Long.class) //類成員註解
public class UserAnnotation {

    @TestA(name="param",id=1,gid=Long.class) //類成員註解
    private Integer age;

    @TestA (name="construct",id=2,gid=Long.class)//構造方法註解
    public UserAnnotation(){
    }

    @TestA(name="public method",id=3,gid=Long.class) //類方法註解
    public void a(){
        Map m = new HashMap(0);
    }

    @TestA(name="protected method",id=4,gid=Long.class) //類方法註解
    protected void b(){
        Map m = new HashMap(0);
    }

    @TestA(name="private method",id=5,gid=Long.class) //類方法註解
    private void c(){
        Map m = new HashMap(0);
    }
}</span>
 

<span style="font-size:18px;">public class ParseAnnotation {

    public static void parseTypeAnnotation() throws ClassNotFoundException {
        Class clazz = Class.forName("com.tan.Test.UserAnnotation");

        Annotation[] annotations = clazz.getAnnotations();
        for (Annotation annotation : annotations) {
            TestA testA = (TestA)annotation;
            System.out.println("id= "+testA.id()+"; name= "+testA.name()+"; gid = "+testA.gid());
        }
    }

    public static void parseMethodAnnotation(){
        Method[] methods = UserAnnotation.class.getDeclaredMethods();
        for (Method method : methods) {
            boolean hasAnnotation = method.isAnnotationPresent(TestA.class);
            if (hasAnnotation) {

                TestA annotation = method.getAnnotation(TestA.class);
                System.out.println("method = " + method.getName()
                        + " ; id = " + annotation.id() + " ; description = "
                        + annotation.name() + "; gid= "+annotation.gid());
            }
        }
    }

    public static void parseConstructAnnotation(){
        Constructor[] constructors = UserAnnotation.class.getConstructors();
        for (Constructor constructor : constructors) {

            boolean hasAnnotation = constructor.isAnnotationPresent(TestA.class);
            if (hasAnnotation) {

                TestA annotation =(TestA) constructor.getAnnotation(TestA.class);
                System.out.println("constructor = " + constructor.getName()
                        + " ; id = " + annotation.id() + " ; description = "
                        + annotation.name() + "; gid= "+annotation.gid());
            }
        }
    }

    //引數註解解析
    public static void parseParameterAnnotation() {
        Field[] fields = UserAnnotation.class.getDeclaredFields();
        for(int i=0;i<fields.length;i++){
            boolean hasAnnotation = fields[i].isAnnotationPresent(TestA.class);
            if(hasAnnotation){
                TestA annotation = fields[i].getAnnotation(TestA.class);
                System.out.println("變數名："+fields[i].getName()+"註解："+annotation.name()+"==="+annotation.id()+"=="+annotation.gid());
            }
        }
    }

    public static void main(String[] args) throws ClassNotFoundException {
//        parseTypeAnnotation();
//        parseMethodAnnotation();
//        parseConstructAnnotation();
        parseParameterAnnotation();
    }
}</span>