Java_log2000_IO2

IO篇entry2

关键词: 文件操作; 流的装配与串行化;

文件操作

File类

例 打开为文件

程序说明

本例每次从源程序文件OpenFile.java中读取512B，存储在缓冲区buffer中，再根据buffer中实际读到的字节数量将它们构造成字符串显示在屏幕上。

import java.io.*;public class OpenFile {    public static void main(String args[]) throws IOException    {        try        {                                          //创建文件输入流对象            FileInputStream  rf = new FileInputStream("OpenFile.java");            int n=512,c=0;            byte buffer[] = new byte[n];            while ((c=rf.read(buffer,0,n))!=-1 )   //读取输入流            {                System.out.print(new String(buffer,0,c));                           }                        rf.close();                            //关闭输入流        }        catch (IOException ioe)        { System.out.println(ioe);}        catch (Exception e)        { System.out.println(e);}    }}

例 写入文件

程序说明

本例用System.in.read(buffer)从键盘输入一串字符，存储在缓冲区buffer中，再以FileOutStream的write(buffer)方法，将buffer中内容写入文件Write1.txt
中；写入文件时，有两种方式，一种是覆盖，一种是追加，在FileOutputStream的构造方法中指出。默认为false，即从头开始写。

import java.io.*;public class Write1 {    public static void main(String args[])    {        try        {   System.out.print("Input: ");            int count,n=512;            byte buffer[] = new byte[n];            count = System.in.read(buffer);        //读取标准输入流            FileOutputStream  wf = new FileOutputStream("Write1.txt");                                                   //创建文件输出流对象            wf.write(buffer,0,count);              //写入输出流            wf.close();                            //关闭输出流            System.out.println("Save to Write1.txt!");        }        catch (IOException ioe)        { System.out.println(ioe);}        catch (Exception e)        { System.out.println(e);}    }}

流的装配与串行化

import java.io.*; public class PrintScreen {     public static void main(String[] args) throws Exception {      PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out), true);        out.println("Hello");     } }

对象串行化与持续性

对象串行化的含义 ：对象的串行化（Serialization）是指通过写出描述自己状态的数值来记录自己的过程。

对象持续性的含义：指能够通过对象的串行化以便将来再生的能力。
程序说明

本例声明Student为序列化的类，该类Save方法创建对象输出流out，并以添加方式向文件直接写入当前对象。display方法中，创建对象输入流in，从文件中直接读取一个对象，获得该对象的类名、接口名等属性，并显示其中的域变量值。

u1.getClass().getName()是得到该对象类的类名；

u1.getClass().getInterfaces()[0])是得到该对象类的第一个实现接口

student

import java.io.*;public class Student implements Serializable    //序列化{    int number=1;    String name;    Student(int number,String n1)    {   this.number = number;        this.name = n1;    }    Student()    { this(0,""); }    void save(String fname)    {        try        {            FileOutputStream fout = new FileOutputStream(fname);            ObjectOutputStream out = new ObjectOutputStream(fout);            out.writeObject(this);               //写入对象            out.close();        }        catch (FileNotFoundException fe){}        catch (IOException ioe){}    }    void display(String fname)    {        try        {            FileInputStream fin = new FileInputStream(fname);            ObjectInputStream in = new ObjectInputStream(fin);            Student u1 = (Student)in.readObject();  //读取对象            System.out.println(u1.getClass().getName()+"  "+                                 u1.getClass().getInterfaces()[0]);            System.out.println("  "+u1.number+"  "+u1.name);            in.close();        }        catch (FileNotFoundException fe){}        catch (IOException ioe){}        catch (ClassNotFoundException ioe) {}    }    public static void main(String arg[])    {        String fname = "Student.obj"; //文件名        Student s1 = new Student(1,"Wang");        s1.save(fname);        s1.display(fname);    }}

student2

import java.io.*;public class Student2 implements Serializable    //序列化{    int number=1;    String name;    Student2(int number,String n1)    {   this.number = number;        this.name = n1;    }    Student2()    { this(0,""); }    void save(String fname)    {        try        {            FileOutputStream fout = new FileOutputStream(fname);            ObjectOutputStream out = new ObjectOutputStream(fout);            out.writeObject(this);               //写入对象            out.close();        }        catch (FileNotFoundException fe){}        catch (IOException ioe){}    }    void display(String fname)    {        try        {            FileInputStream fin = new FileInputStream(fname);            ObjectInputStream in = new ObjectInputStream(fin);            Student2 u1 = (Student2)in.readObject();  //读取对象            System.out.println(u1.getClass().getName()+"  "+                                 u1.getClass().getInterfaces()[0]);            System.out.println("  "+u1.number+"  "+u1.name);            in.close();        }        catch (FileNotFoundException fe){}        catch (IOException ioe){}        catch (ClassNotFoundException ioe) {}    }    public static void main(String arg[])    {        String fname = "student2.obj"; //文件名        Student2 s1 = new Student2(1,"Wang");        s1.save(fname);        s1.display(fname);    }}