java 输入输出 对象序列化implements Serializable与反序列化:ObjectOutputStream.writeObject() ;objectInputStream.readObject() ;serialVersionUID字段注意
对象序列化
对象序列化的目标是将对象保存到磁盘中,或允许在网络中直接传输对象。对象序列化机制允许把内存中的 Java 对象转换成平台无关的二进制流,从而允许把这种二进制流持久地保存在磁盘上,通过网络将这种二进制流传输到另1个网络节点。其他程序一旦获得了这种二进制流(无论是从磁盘中获取的,还是通过网络获取的) ,都可以将这种二进制流恢复成原来的 Java 对象
如何来使用对象序列化?
前提:
首先,一个类要被序列化,那么它必须实现如下两个接口之一:
- Serializable
- Extemalizable
实现着两个接口的作用,其实就是就是标记一个对象是否可以被序列化。所以比如我们有一个类需要被序列化,我们实现Serializable接口就行,无需实现任何方法。
序列化工具类:ObjectOutputStream
方法:
- writeObject()
反序列化工具类:objectInputStream
方法:
- readObject()
示例:存储Person类对象
import java.io.*; /** * @ClassName ObjectOutputStreamWriteObjectExample * @projectName: object1 * @author: Zhangmingda * @description: Person 类实现序列化接口 * date: 2021/4/18. */ public class ObjectOutputStreamWriteObjectExample { //实现接口Serializable可以序列化 private static class Person implements Serializable { String name; int age; public Person(String name, int age) { this.name = name; this.age = age; } @Override public String toString() { return "Person{" + "name='" + name + '\'' + ", age=" + age + '}'; } } //序列化方法 private static void writeObject(Person person,String dstPath) { try(ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(dstPath))){ objectOutputStream.writeObject(person); } catch (IOException e) { e.printStackTrace(); } } //反序列化方法 private static<T> void readObject(String srcPath){ try(ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(srcPath))){ T person = (T) objectInputStream.readObject(); System.out.println(person.getClass()); System.out.println(person); /** * class ObjectOutputStreamWriteObjectExample$Person * Person{name='钱老大', age=30} */ } catch (IOException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } } public static void main(String[] args) { Person person = new Person("钱老大",30); String dstPath = "输入输出文件读写/src/test/output/object-save.txt"; writeObject(person,dstPath); String srcPath = "输入输出文件读写/src/test/output/object-save.txt"; readObject(srcPath); } }
示例:带有引用变量的对象序列化
引用类型也必须是可以序列化的。
import java.io.*; /** * @ClassName ObjectOutputStreamWriteObjectExample * @projectName: object1 * @author: Zhangmingda * @description: Person 类实现序列化接口 * date: 2021/4/18. */ public class ObjectOutputStreamWriteObjectExample { //实现接口Serializable可以序列化 private static class Person implements Serializable { String name; int age; Job job; public Person(String name, int age, Job job) { this.name = name; this.age = age; this.job = job; } public Person(String name, int age) { this.name = name; this.age = age; } @Override public String toString() { return "Person{" + "name='" + name + '\'' + ", age=" + age + ", job=" + job.getName() + '}'; } } private static class Job implements Serializable { private String name; public Job(String name) { this.name = name; } public String getName() { return name; } } //序列化方法 private static void writeObject(Person person,String dstPath) { try(ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(dstPath))){ objectOutputStream.writeObject(person); } catch (IOException e) { e.printStackTrace(); } } //反序列化方法 private static<T> void readObject(String srcPath){ try(ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(srcPath))){ T person = (T) objectInputStream.readObject(); System.out.println(person.getClass()); System.out.println(person); /** * class ObjectOutputStreamWriteObjectExample$Person * Person{name='钱老大', age=30, job=教师} */ } catch (IOException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } } public static void main(String[] args) { Person person = new Person("钱老大",30,new Job("教师")); String dstPath = "输入输出文件读写/src/test/output/object-save.txt"; writeObject(person,dstPath); String srcPath = "输入输出文件读写/src/test/output/object-save.txt"; readObject(srcPath); } }
指定哪些字段不需要序列化
比如上面的Person对象,可能有的女生认为年龄是一个秘密,不应该被序列化,怎么办?
用transient关键字修饰对应的字段就OK了
示例:private transient int age;
存入:Person{name='钱老大', age=30, job=教师}
读取:Person{name='钱老大', age=0, job=教师} 【不被反序列化的字段置为 对应数据类型默认值】
//序列化写入到文件时transient 未设置,读取时添加了transient,等于对象的类在写入后,读取之前又发生了变化,然后反序列化读取发生
错误类似:local class incompatible: stream classdesc serialVersionUID ......
解决:类在创建时 添加serialVersionUID字段来保证类发生变化后,也能反序列化成功(不被反序列化的字段置为 对应数据类型默认值)
即:类的升级
import java.io.*; /** * @ClassName ObjectOutputStreamWriteObjectExample * @projectName: object1 * @author: Zhangmingda * @description: Person 类实现序列化接口 * date: 2021/4/18. */ public class ObjectOutputStreamWriteObjectExample { //实现接口Serializable可以序列化 private static class Person implements Serializable { private static final long serialVersionUID = 769204331117184540L; private String name; private transient int age; private Job job; public Person(String name, int age, Job job) { this.name = name; this.age = age; this.job = job; } public Person(String name, int age) { this.name = name; this.age = age; } @Override public String toString() { return "Person{" + "name='" + name + '\'' + ", age=" + age + ", job=" + job.getName() + '}'; } } private static class Job implements Serializable { private String name; public Job(String name) { this.name = name; } public String getName() { return name; } } //序列化方法 private static void writeObject(Person person,String dstPath) { try(ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(dstPath))){ objectOutputStream.writeObject(person); } catch (IOException e) { e.printStackTrace(); } } //反序列化方法 private static<T> void readObject(String srcPath){ try(ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(srcPath))){ T person = (T) objectInputStream.readObject(); System.out.println(person.getClass()); System.out.println(person); /** * class ObjectOutputStreamWriteObjectExample$Person * Person{name='钱老大', age=30, job=教师} */ } catch (IOException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } } public static void main(String[] args) { // Person person = new Person("钱老大",30,new Job("教师")); // String dstPath = "输入输出文件读写/src/test/output/object-save.txt"; // writeObject(person,dstPath); String srcPath = "输入输出文件读写/src/test/output/object-save.txt"; readObject(srcPath); } }
posted on 2021-04-18 22:32 zhangmingda 阅读(139) 评论(0) 编辑 收藏 举报