java使用IO讀寫文件總結

每次用到IO的讀寫文件都老忘記寫法，都要翻過往筆記，今天總結下，省的之後老忘。java讀寫文件的IO流分兩大類，字節流和字符流，基類分別是字符：Reader和Writer；字節：InputStream和OutPutStream，

一、字符流分爲FileReader和FileWrtier，這兩個的父類是InputStreamReader和OutStreamWrtier

二、字節流分爲FileInputStream和FileOutPutStream

關係網：

Reader->InputStreamReader->FileReader

Reader->BufferedReader

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Writer->OutputStreamWriter->FileWriter

Writer->BufferedWriter

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InputStream->FileInputStream。FileInputStream 用於讀取諸如圖像數據之類的原始字節流。要讀取字符流，請考慮使用 FileReader。

InputStream->FilterInputStream->BufferedInputStream

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OutputStream->FileOutputStream。FileOutputStream 用於寫入諸如圖像數據之類的原始字節的流。要寫入字符流，請考慮使用 FileWriter

OutputStream->FilterOutputStream->BufferedOutputStream

流的程序通常分如下四步：

1.建立文件對象 File file = new File("xxx.txt");

2.用流裝載文件 FileReader fr = new FileReader(file);

3.若是用緩衝區，則用緩衝區裝載流，用緩衝區是爲了提升讀寫性能 BufferReader br = new BufferReader(fr);

4.開始讀寫操做 String s = null; StringBuffer sb = new StringBuffer(); while((s=br.readLine()!=null) { sb.append(s); } 若是遇到字節流要轉換成字符流，則在緩衝區前加一步 InputStreamReader isr = new InpuStreamReader(InputStream in); 或者須要編碼轉換的，則在緩衝區前加一步 InputStreamReader isr = new InpuStreamReader(InputStream in，Charset cs);

下面的代碼分別是複製文本文件、圖像文件。字節轉換字符的操做：

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 建立時間：2016年4月12日 下午12:03:37 
 * 類說明 
 */
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();
    }
}