Java反射类private私有变量Map并赋值

系统管理员 2023-10-14 03:14 36阅读 0赞

import java.util.LinkedHashMap;
    import java.util.Map;
    
    public class MyObj {
        private String KEY = "NAME";
    
        //目标是通过反射在外部访问cache
        private Map<String, String> cache = new LinkedHashMap<>();
    
        public MyObj() {
            cache.put(KEY, "fly");
        }
    
        public void print() {
            System.out.println(cache.get(KEY));
        }
    }

import java.lang.reflect.Field;
    import java.util.Map;
    import java.util.Set;
    
    public class Main {
        public static void main(String[] args) {
            MyObj obj = new MyObj();
            System.out.println("反射前");
            obj.print();
            System.out.println("===");
    
            try {
                Field privateField = MyObj.class.getDeclaredField("cache");
                privateField.setAccessible(true);
    
                Map map = (Map) privateField.get(obj);
    
                System.out.println("-");
                Set<String> sets = map.keySet();
                Object[] keys = sets.toArray();
                for (Object k : keys) {
                    System.out.println("遍历key-旧值:" + k + "->" + map.get(k.toString()));
    
                    //对MyObj里面的cache设置新值。
                    map.put(k, "phil");
                }
                System.out.println("--");
    
    
                System.out.println("反射后");
                obj.print();
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
    }

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