1. 为什么需要序列化？

因为如果不实现序列化，那么则无法反序列化

2. 序列化使用场景？

1. 需要存储对象，比如说我现在需要把内存中的对象暂时写入硬盘，等我系统启用时在加载到内存反序列化后继续使用。
2. 需要远程传输对象，则需要实现序列化接口，大多在socket网络套接字编程场景中比较常见， 有同学可能说，我经常使用socket传输数据，确没有实现序列化接口，因为很多情况下我们都是传输的String字符串，而在Java中String已经实现了Serializable接口

3. 序列化常见出错问题？

   不实现序列化接口进行保存对象会出现如下错误，可以通过实现Serializable接口解决问题。

Exception in thread "main" java.io.NotSerializableException: home.s.Rule    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)    at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)    at home.s.Serial.main(Serial.java:13)    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)    at java.lang.reflect.Method.invoke(Method.java:498)    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

修改序列号id则会出现如下问题：

Exception in thread "main" java.io.InvalidClassException: home.s.Rule; local class incompatible: stream classdesc serialVersionUID = 1234000, local class serialVersionUID = 123400    at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:616)    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1630)    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1521)    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1781)    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1353)    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:373)    at home.s.DESerial.main(DESerial.java:13)    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)    at java.lang.reflect.Method.invoke(Method.java:498)    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

出现这个问题是因为序列号被认为改动导致。这时可能大多数同学会说，可不可以不使用序列号，而使用Java本身默认的。如下是Java默认生成序列号源码，大概意思请自行阅读。

/**     * Return the serialVersionUID for this class.  The serialVersionUID     * defines a set of classes all with the same name that have evolved from a     * common root class and agree to be serialized and deserialized using a     * common format.  NonSerializable classes have a serialVersionUID of 0L.     *     * @return  the SUID of the class described by this descriptor     */    public long getSerialVersionUID() {        // REMIND: synchronize instead of relying on volatile?        if (suid == null) {            suid = AccessController.doPrivileged(                new PrivilegedAction
    
     () {                    public Long run() {                        return computeDefaultSUID(cl);                    }                }            );        }        return suid.longValue();    }
    

但是这里还是强烈建议使用一个序列化版本号，因为默认的版本号非常敏感，并且依赖于编译器，如果实体类在序列化之前和之后数据结构有所改变，则会导致如下问题：

Exception in thread "main" java.io.InvalidClassException: home.s.Rule; local class incompatible: stream classdesc serialVersionUID = -1031401772392262459, local class serialVersionUID = 7635324993874063726    at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:616)    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1630)    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1521)    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1781)    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1353)    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:373)    at home.s.DESerial.main(DESerial.java:13)    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)    at java.lang.reflect.Method.invoke(Method.java:498)    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

4. 具体测试源码如下：

   实体类：

package home.s;import java.io.Serializable;public class Rule  implements Serializable{    private static final long serialVersionUID = 1234000L;    public Rule(Long id, String type) {        this.id = id;        this.type = type;    }    private Long id;    private String type;   // private String name;    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getType() {        return type;    }    public void setType(String type) {        this.type = type;    } /*   public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }*/}

序列化

Rule rule = new Rule(1232L, "asdf");        FileOutputStream fileOutputStream = new FileOutputStream(new File("d:\\222.txt"));        ObjectOutputStream oos = new ObjectOutputStream(fileOutputStream);        oos.writeObject(rule);        oos.flush();        fileOutputStream.close();

反序列化

FileInputStream fis = new FileInputStream(new File("D:\\222.txt"));        ObjectInputStream ois = new ObjectInputStream(fis);        Rule o = (Rule) ois.readObject();        System.out.println(Json.toJson(o));