一次搞懂序列化和反序列化

1. 为什么需要序列化？

1. 序列化使用场景？

1. 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<Long>() {
                    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)

1. 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));