Java IO流整理

一、InputStream/OutputStream 和 Reader/Writer
辨析：

InputStream/OutputStream：1）抽象类；2）面向字节 形式的I/O操作 （8位字节流）。

Reader/Writer：1）抽象类；2）面向字符的I/O操作（16位的Unicode字符）。

InputStreamReader：可以将InputStream转换为 Reader;

OutputStreamWriter：可以将OutputStream转换为Writer;

注：图中细箭头标识实现接口，粗箭头标识继承父类。






示例代码：

package javaio01;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
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.PrintWriter;

/**
 * 使用 字符流和字节流两种方式，读取文本显示出来，并保存到指定的文件中；
 * */
public class ReaderTest {
	
	public static void main(String[] args) {
		//methodBytes("a.txt");
		methodString("a.txt");
	}
	/**
	 * First:字节流
	 * */
	public static void methodBytes(String position) {
		FileInputStream fileIn = null;
		try {
			fileIn = new FileInputStream(position);
			
			int n = 1024;
			byte inbuffer[] = new byte[n];
			
			StringBuffer filecontent = new StringBuffer();
			while(fileIn.read(inbuffer,0,n) != -1)
			{
				filecontent.append(new String(inbuffer));
			}
			System.out.println("字节流读取文件内容：\n"+filecontent.toString());
			fileIn.close();//关闭输入流 释放资源
			
			//字节流读取转为字符流读取
			BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(position))); 
			
			String str = null;
			StringBuffer strbf = new StringBuffer("");
			while((str = br.readLine()) != null)
			{
				strbf.append(str);
			}
			br.close();
			System.out.println("\n字节流读取转为字符流读取:\n"+strbf.toString());
			
			
			
			//写入文件b中
			FileOutputStream os = new FileOutputStream("b.txt"); 
			//写入输出流
			os.write(filecontent.toString().getBytes());
			//关闭输出流
			os.close();
			System.out.println("\n文件a的内容已经保存到b文件中去了！！！");
			
		} catch (FileNotFoundException e) {
			System.out.println("file not exit!");
		} catch (IOException e) {
			e.printStackTrace();
		}
		
		
	}
	/**
	 * Second:字符流
	 * */
	public static void methodString(String position) {
		try {
			/*1th*/
			//BufferedReader br = new BufferedReader(new FileReader(new File("a.tx")));
			
			/*2th*/
			//FileReader fr = new FileReader(position);
			//BufferedReader br = new BufferedReader(new FileReader("a.tx"));
			
			/*3th ： InputStreamReader：可以将InputStream转换为	Reader;*/
			//将字节流转换成字符流
			BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(position)));

			String str = null;
			StringBuffer filecontent = new StringBuffer();
			while((str = br.readLine()) != null)
			{
				filecontent.append(str);
			}
			
			System.out.println("\n字节流读取文件内容：\n"+filecontent.toString());
			br.close();//关闭输入流 释放资源
			
			/*********************/
			
			//将字符流 保存到文本中
			BufferedWriter brt = new BufferedWriter(new FileWriter("b.txt"),1024);
			brt.write(filecontent.toString());
			brt.flush();
			brt.close();
			System.out.println("\n文件保存成功！！！\n");
			
			/*********************/
			PrintWriter pr = new PrintWriter(new FileOutputStream("aa.txt"));
			pr.println("wwwwwwwwwwwwwwwww");
			pr.flush();
			pr.close();
			
			
		} catch (FileNotFoundException e) {
			System.out.println("file not exit!");
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}

文件流与字节数组的互转：

/** 
     * 获得指定文件的byte数组 
     */  
    private byte[] getBytes(String filePath){  
        byte[] buffer = null;  
        try {  
            File file = new File(filePath);  
            FileInputStream fis = new FileInputStream(file);  
            ByteArrayOutputStream bos = new ByteArrayOutputStream(1000);  
            byte[] b = new byte[1000];  
            int n;  
            while ((n = fis.read(b)) != -1) {  
                bos.write(b, 0, n);  
            }  
            fis.close();  
            bos.close();  
            buffer = bos.toByteArray();  
        } catch (FileNotFoundException e) {  
            e.printStackTrace();  
        } catch (IOException e) {  
            e.printStackTrace();  
        }  
        return buffer;  
    }
    
    /** 
     * 根据byte数组，生成文件 
     */  
    public static void getFile(byte[] bfile, String filePath,String fileName) {  
        BufferedOutputStream bos = null;  
        FileOutputStream fos = null;  
        File file = null;  
        try {  
            File dir = new File(filePath);  
            if(!dir.exists()&&dir.isDirectory()){//判断文件目录是否存在  
                dir.mkdirs();  
            }  
            file = new File(filePath+"\\"+fileName);  
            fos = new FileOutputStream(file);  
            bos = new BufferedOutputStream(fos);  
            bos.write(bfile);  
        } catch (Exception e) {  
            e.printStackTrace();  
        } finally {  
            if (bos != null) {  
                try {  
                    bos.close();  
                } catch (IOException e1) {  
                    e1.printStackTrace();  
                }  
            }  
            if (fos != null) {  
                try {  
                    fos.close();  
                } catch (IOException e1) {  
                    e1.printStackTrace();  
                }  
            }  
        }  
    }