java使用IO读写文件总结

2022-04-03 03:04:18

每次用到IO的读写文件都老忘记写法，都要翻过往笔记，今天总结下，省的以后老忘。java读写文件的IO流分两大类，字节流和字符流，基类分别是字符：Reader和Writer；字节：InputStream和OutPutStream，

1、字符流分为FileReader和FileWrtier，这两个的父类是InputStreamReader和OutStreamWrtier

2、字节流分为FileInputStream和FileOutPutStream

关系网：

Reader->InputStreamReader->FileReader

Reader->BufferedReader

Writer->OutputStreamWriter->FileWriter

Writer->BufferedWriter

InputStream->FileInputStream。FileInputStream 用于读取诸如图像数据之类的原始字节流。要读取字符流，请考虑使用 FileReader。

InputStream->FilterInputStream->BufferedInputStream

OutputStream->FileOutputStream。FileOutputStream 用于写入诸如图像数据之类的原始字节的流。要写入字符流，请考虑使用 FileWriter

OutputStream->FilterOutputStream->BufferedOutputStream

流的程序一般分以下四步：

1.创建文件对象 File file = new File("xxx.txt");

2.用流装载文件 FileReader fr = new FileReader(file);

3.如果用缓冲区，则用缓冲区装载流，用缓冲区是为了提高读写性能 BufferReader br = new BufferReader(fr);

4.开始读写操作 String s = null; StringBuffer sb = new StringBuffer(); while((s=br.readLine()!=null) { sb.append(s); } 如果遇到字节流要转换成字符流，则在缓冲区前加一步 InputStreamReader isr = new InpuStreamReader(InputStream in); 或者需要编码转换的，则在缓冲区前加一步 InputStreamReader isr = new InpuStreamReader(InputStream in，Charset cs);

下面的代码分别是复制文本文件、图像文件。字节转换字符的操作：

package com.io;

import java.io.BufferedInputStream;

import java.io.BufferedOutputStream;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.UnsupportedEncodingException;

import com.sun.org.apache.bcel.internal.generic.NEW;

/**

 * @author QiaoJiafei

 * @version 创建时间：2016年4月12日 下午12:03:37

 * 类说明

 */

public class TestIO {

    public static void main(String[] args) throws IOException {

        testFileReader();

        testFileInputStream();

    }

    private static void testInputStream() throws IOException {

        InputStream ist = System.in;

        BufferedReader br = new BufferedReader(new InputStreamReader(ist,"uft-8"));

        String s = "";

        while ((s=br.readLine())!=null) {

            System.out.println(s);

        }

        br.close();

    }

    private static void testFileReader() throws IOException {

        FileReader reader = new FileReader("/Users/qiaojiafei/Documents/test.txt");

        FileWriter writer = new FileWriter("/Users/qiaojiafei/Documents/test_copy.txt");

        BufferedReader bReader = new BufferedReader(reader);

        BufferedWriter bWriter = new BufferedWriter(writer);

        String temp = "";

        while((temp=bReader.readLine())!=null) {

            bWriter.write(temp);

        }

        bWriter.flush();

        bWriter.close();

        bReader.close();

    }

    private static void testFileInputStream() throws IOException {

        FileInputStream fis = new FileInputStream("/Users/qiaojiafei/Documents/zz.png");

        FileOutputStream fos = new FileOutputStream("/Users/qiaojiafei/Documents/zz_copy.png");

        BufferedInputStream bInputStream = new BufferedInputStream(fis);

        BufferedOutputStream bOutputStream = new BufferedOutputStream(fos);

        int temp = 0;

        while((temp=bInputStream.read()) != -1) {

            bOutputStream.write(temp);

        }

        bOutputStream.flush();

        bOutputStream.close();

        bInputStream.close();

    }

}

码农公寓

相关文章