Java反射中Annotation的

- 日理万妓 2022-07-16 08:30 179阅读 0赞

定义Annotation的构造方法的类：

import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    /**
     * Created by cuboo on 2016/10/11.
     */
    
    //用于构造方法
    @Target(ElementType.CONSTRUCTOR)
    //运行时加载贷JVM中
    @Retention(RetentionPolicy.RUNTIME)
    public @interface constructor_annotation {
        //定义默认值的成员
        String value() default "默认构造方法";
    }

定义Annotation的变量、方法、参数的类：

import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    /**
     * Created by cuboo on 2016/10/11.
     */
    //用于字段、方法、参数
    @Target({ElementType.FIELD,ElementType.METHOD,ElementType.PARAMETER} )
    //运行时加载到JVM中
    @Retention(RetentionPolicy.RUNTIME)
    public @interface field_method_parameter_annotation {
        String describe();
        Class type() default void.class;
    }

运用定义Annotation的类：

/**
     * Created by cuboo on 2016/10/11.
     */
    
    public class annotation_class {
          //注释变量
        @field_method_parameter_annotation(describe = "编号",type = int.class)
        int id;
        @field_method_parameter_annotation(describe = "姓名",type = String.class)
        String name;
    
        //构造无参数方法
        @constructor_annotation()
        annotation_class(){
        }
        //构造有参数方法
        @constructor_annotation()
        annotation_class(@field_method_parameter_annotation(describe = "编号",type = int.class) int id,
                         @field_method_parameter_annotation(describe = "姓名",type = String.class) String name){
            this.id = id;
            this.name = name;
        }
    
        //注释方法
        @field_method_parameter_annotation(describe = "获得编号",type = int.class)
        public int getId(){
            return id;
        }
        @field_method_parameter_annotation(describe = "获得姓名",type = String.class)
        public String getName() {
            return name;
        }
    
        //注释方法的参数
        @field_method_parameter_annotation(describe = "设置编号")
        public void setId(@field_method_parameter_annotation(describe = "编号",type = int.class) int id) {
            this.id = id;
        }
        @field_method_parameter_annotation(describe = "设置姓名")
        public void setName(@field_method_parameter_annotation(describe = "姓名",type = String.class) String name) {
            this.name = name;
        }
    }

访问Annotation的内容类：

import java.lang.annotation.Annotation;
    import java.lang.reflect.Constructor;
    import java.lang.reflect.Field;
    import java.lang.reflect.Method;
    
    /**
     * Created by cuboo on 2016/10/11.
     */
    public class access_annotation {
        public static void main(String agrs[]){
    //       get_constructor();
    //        get_field();
            get_method();
        }
    
        public static void get_constructor(){
            annotation_class exam = new annotation_class();
            Class examC = exam.getClass();
            Constructor[] constructors = examC.getDeclaredConstructors();
    
            for (int i = 0; i < constructors.length; i++) {
                Constructor constructor = constructors[i];
                //查看指定类型的注释
                if (constructor.isAnnotationPresent(constructor_annotation.class)){
                    constructor_annotation ca = (constructor_annotation) constructor.getAnnotation(constructor_annotation.class);
                    //获得注释信息
                    System.out.println(ca.value());
                }
    
                //获得参数的注释
                Annotation[][] paras = constructor.getParameterAnnotations();
                for (int j = 0; j < paras.length; j++) {
                    //获得指定注释参数的长度
                    int length = paras[j].length;
                    if (length == 0){
                        System.out.println("未添加注释参数");
                    }else {
                        for (int k = 0; k < length; k++) {
                            //获得参数的注释
                            field_method_parameter_annotation fp = (field_method_parameter_annotation) paras[j][k];
                            System.out.println("参数描述："+fp.describe());
                            System.out.println("参数类型："+fp.type());
                        }
                    }
                }
            }
    
        }
        public static void get_field(){
            annotation_class exam = new annotation_class();
            Class examC = exam.getClass();
            Field[] fields = examC.getDeclaredFields();
            for (int i = 0; i < fields.length; i++) {
                Field field = fields[i];
                //查看指定注释
                if (field.isAnnotationPresent(field_method_parameter_annotation.class)){
                    field_method_parameter_annotation fp = field.getAnnotation(field_method_parameter_annotation.class);
                    System.out.println("变量描述："+fp.describe());
                    System.out.println("变量类型："+fp.type());
                }
            }
    
        }
        public static void get_method(){
            annotation_class exam = new annotation_class();
            Class examC = exam.getClass();
            Method[] methods = examC.getDeclaredMethods();
            for (int i = 0; i < methods.length; i++) {
                Method method = methods[i];
                //获得指定的注释
                if (method.isAnnotationPresent(field_method_parameter_annotation.class)){
                    field_method_parameter_annotation fp = method.getAnnotation(field_method_parameter_annotation.class);
                    System.out.println("方法的描述："+fp.describe());
                    System.out.println("方法的返回类型："+fp.type());
                }
    
                //获得参数的注释
                Annotation[][] paras = method.getParameterAnnotations();
                for (int j = 0; j < paras.length; j++) {
                    //获得指定注释参数的长度
                    int length = paras[j].length;
                    if (length == 0){
                        System.out.println("未添加注释参数");
                    }else {
                        for (int k = 0; k < length; k++) {
                            //获得参数的注释
                            field_method_parameter_annotation fp = (field_method_parameter_annotation) paras[j][k];
                            System.out.println("参数描述："+fp.describe());
                            System.out.println("参数类型："+fp.type());
                        }
                    }
                }
            }
        }
    }