java使用IO读写文件总结

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();
}
}