Java 输入/输出——字节流和字符流

1、流的分类

　　（1）输入流和输出流（划分输入/输出流时是从程序运行所在内存的角度来考虑的）

　　　　输入流：只能从中读取数据，而不能向其写入数据。

　　　　输出流：只能向其写入数据，而不能从中读取数据。

　　　　输入流主要由InputStream和Reader作为基类，输出流主要由OutputStream和Writer作为基类。它们都是抽象基类，无法直接创建实例。

　　（2）字节流和字符流

　　　　字节流和字符流的用法几乎完全一样，区别在于字节流和字符流操作的数据单元不同——字节流操作的数据单元是8-bit的字节，而字符流操作的数据单元是16-bit的字符。

　　　　字节流主要由InputStream和OutputStream作为基类，而字符流则主要由Reader和Writer作为基类。

　　（3）节点流和处理流

　　　　可以从/向一个特定的IO设备（如磁盘、网络）读/写数据的流，称为节点流，节点流也被称为低级流。

　　　　处理流则用于对一个已经存在的流进行连接或封装，通过封装后的流来实现数据读/写功能。处理流也被称为高级流。

2、InputStream和Reader

　　在InputStream里包含你的方法如下：

All Methods Instance Methods Abstract Methods Concrete Methods 

Modifier and Type	Method	Description
int	available​()	Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream.
void	close​()	Closes this input stream and releases any system resources associated with the stream.
void	mark​(int readlimit)	Marks the current position in this input stream.（在记录指针当前位置记录一个标记（mark））
boolean	markSupported​()	Tests if this input stream supports the mark and reset methods.
abstract int	read​()	Reads the next byte of data from the input stream.（字节数据可以直接转换为int类型）
int	read​(byte[] b)	Reads some number of bytes from the input stream and stores them into the buffer array b.（最多读取b.length个字节的数据，并将其存储在字节数组b中，放入数组b中时，返回实际读取的字节数）
int	read​(byte[] b, int off, int len)	Reads up to len bytes of data from the input stream into an array of bytes.（最多读取b.length个字节的数据，并将其存储在字节数组b中，放入数组b中时，并不是从数组起点开始，而是从off位置开始，返回实际读取的字节数）
byte[]	readAllBytes​()	Reads all remaining bytes from the input stream.
int	readNBytes​(byte[] b, int off, int len)	Reads the requested number of bytes from the input stream into the given byte array.
void	reset​()	Repositions this stream to the position at the time the mark method was last called on this input stream.（将此流的记录指针重新定位到上一次记录标记（mark）的位置）
long	skip​(long n)	Skips over and discards n bytes of data from this input stream.（记录指针向前移动n个字节/字符）
long	transferTo​(OutputStream out)	Reads all bytes from this input stream and writes the bytes to the given output stream in the order that they are read.

　　在Reader里包含方法如下：

Constructors 

Modifier	Constructor	Description
protected	Reader​()	Creates a new character-stream reader whose critical sections will synchronize on the reader itself.
protected	Reader​(Object lock)	Creates a new character-stream reader whose critical sections will synchronize on the given object.

Modifier and Type	Method	Description
abstract void	close​()	Closes the stream and releases any system resources associated with it.
void	mark​(int readAheadLimit)	Marks the present position in the stream.
boolean	markSupported​()	Tells whether this stream supports the mark() operation.
int	read​()	Reads a single character.
int	read​(char[] cbuf)	Reads characters into an array.（最多读取cbuf.length个字符的数据，并将其存储在字符数组cbuf中，返回实际读取的字符数）
abstract int	read​(char[] cbuf, int off, int len)	Reads characters into a portion of an array.
int	read​(CharBuffer target)	Attempts to read characters into the specified character buffer.
boolean	ready​()	Tells whether this stream is ready to be read.
void	reset​()	Resets the stream.
long	skip​(long n)	Skips characters.

 　　程序直到read(char[] cbuf)或者read(byte[] b)方法返回-1，即表明到了输入流的结束点。

package com.zyjhandsome.io;

import java.io.*;

public class FileInputStreamTest {

    public static void main(String[] args){
        // 用于 保存呢实际读取的字节数
        int hasRead = 0;
        // 创建字节输入流
        FileInputStream fis = null;
        try {
            fis = new FileInputStream("D:\zhaoyingjun\eclipse-workspace\CollectionTest\src\com\zyjhandsome\io\FileInputStreamTest.java");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.println("找不到指定文件");
            System.exit(-1);
        }
        
        try {
            long num = 0;
            while ((hasRead = fis.read()) != -1)
            {
                System.out.print(((char)hasRead));
                num++;
            }
            fis.close();
            System.out.println();
            System.out.println("共读取了" + num + "个字节");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.print("文件读取错误");
            System.exit(-1);
        }        
    }
}

　　输出内容（因为是按照字节输出，因此对于中文（字符型）会读取时会出现？的现象）：

package com.zyjhandsome.io;

import java.io.*;

public class FileInputStreamTest {

    public static void main(String[] args){
        // ???? ±???????????????×?????
        int hasRead = 0;
        // ???¨×????????÷
        FileInputStream fis = null;
        try {
            fis = new FileInputStream("D:\zhaoyingjun\eclipse-workspace\CollectionTest\src\com\zyjhandsome\io\FileInputStreamTest.java");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.println("?????????¨????");
            System.exit(-1);
        }
        
        try {
            long num = 0;
            while ((hasRead = fis.read()) != -1)
            {
                System.out.print(((char)hasRead));
                num++;
            }
            fis.close();
            System.out.println();
            System.out.println("????????" + num + "??×???");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.print("?????????í?ó");
            System.exit(-1);
        }        
    }
}

共读取了940个字节

package com.zyjhandsome.io;

import java.io.FileInputStream;
import java.io.*;

public class FileReaderTest {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        // 用于保存呢实际读取的字节数
        int hasRead = 0;
        // 创建字节输入流
        FileReader fr = null;
        try {
            fr = new FileReader("D:\zhaoyingjun\eclipse-workspace\CollectionTest\src\com\zyjhandsome\io\FileInputStreamTest.java");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.println("找不到指定文件");
            System.exit(-1);
        }
        
        try {
            long num = 0;
            while ((hasRead = fr.read()) != -1)
            {
                System.out.print(((char)hasRead));
                num++;
            }
            fr.close();
            System.out.println();
            System.out.println("共读取了" + num + "个字符");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.print("文件读取错误");
            System.exit(-1);
        }
    }

}

　　输出内容：

package com.zyjhandsome.io;

import java.io.*;

public class FileInputStreamTest {

    public static void main(String[] args){
        // 用于保存呢实际读取的字节数
        int hasRead = 0;
        // 创建字节输入流
        FileInputStream fis = null;
        try {
            fis = new FileInputStream("D:\zhaoyingjun\eclipse-workspace\CollectionTest\src\com\zyjhandsome\io\FileInputStreamTest.java");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.println("找不到指定文件");
            System.exit(-1);
        }
        
        try {
            long num = 0;
            while ((hasRead = fis.read()) != -1)
            {
                System.out.print(((char)hasRead));
                num++;
            }
            fis.close();
            System.out.println();
            System.out.println("共读取了" + num + "个字节");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.print("文件读取错误");
            System.exit(-1);
        }
    }
}

共读取了897个字符

package com.zyjhandsome.io;

import java.io.*;

public class FileReaderTester2 {

    public static void main(String[] args) throws IOException{
        // TODO Auto-generated method stub
        try {
            // 创建字节输入流
            FileReader fr = new FileReader("D:\zhaoyingjun\eclipse-workspace\CollectionTest\src\com\zyjhandsome\io\FileInputStreamTest.java");
            // 创建一个 长度为32的“竹筒”
            char[] cbuf = new char[32];
            // 用于保存呢实际读取的字节数
            int hasRead = 0;
            // 使用循环来重复读取字符数
            while ((hasRead = fr.read(cbuf)) > 0)
            {
                // 取出“竹筒”中的水滴（字符），将字符数组转换成字符串输入
                System.out.print(new String(cbuf, 0, hasRead));
            }
            fr.close();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.println("找不到指定文件");
            System.exit(-1);
        }
    }
}

　　输出结果：

package com.zyjhandsome.io;

import java.io.*;

public class FileInputStreamTest {

    public static void main(String[] args){
        // 用于保存呢实际读取的字节数
        int hasRead = 0;
        // 创建字节输入流
        FileInputStream fis = null;
        try {
            fis = new FileInputStream("D:\zhaoyingjun\eclipse-workspace\CollectionTest\src\com\zyjhandsome\io\FileInputStreamTest.java");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.println("找不到指定文件");
            System.exit(-1);
        }
        
        try {
            long num = 0;
            while ((hasRead = fis.read()) != -1)
            {
                System.out.print(((char)hasRead));
                num++;
            }
            fis.close();
            System.out.println();
            System.out.println("共读取了" + num + "个字节");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.print("文件读取错误");
            System.exit(-1);
        }
    }
}

3、OutputStream和Writer

 　　OutputStream里方法包含如下：

Modifier and Type	Method	Description
void	close​()	Closes this output stream and releases any system resources associated with this stream.
void	flush​()	Flushes this output stream and forces any buffered output bytes to be written out.
void	write​(byte[] b)	Writes b.length bytes from the specified byte array to this output stream.
void	write​(byte[] b, int off, int len)	Writes len bytes from the specified byte array starting at offset off to this output stream.
abstract void	write​(int b)	Writes the specified byte to this output stream.

　　Writer里包含方法如下：

Constructors 

Modifier	Constructor	Description
protected	Writer​()	Creates a new character-stream writer whose critical sections will synchronize on the writer itself.
protected	Writer​(Object lock)	Creates a new character-stream writer whose critical sections will synchronize on the given object.

Modifier and Type	Method	Description
Writer	append​(char c)	Appends the specified character to this writer.
Writer	append​(CharSequence csq)	Appends the specified character sequence to this writer.
Writer	append​(CharSequence csq, int start, int end)	Appends a subsequence of the specified character sequence to this writer.
abstract void	close​()	Closes the stream, flushing it first.
abstract void	flush​()	Flushes the stream.
void	write​(char[] cbuf)	Writes an array of characters.
abstract void	write​(char[] cbuf, int off, int len)	Writes a portion of an array of characters.
void	write​(int c)	Writes a single character.
void	write​(String str)	Writes a string.
void	write​(String str, int off, int len)	Writes a portion of a string.

package com.zyjhandsome.io;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileOutputStreamTest2 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int hasRead = 0;
        byte[] bbuf = new byte[32];
        FileInputStream fis = null;
        FileOutputStream fos = null;
        try {
            fis = new FileInputStream("D:\zhaoyingjun\eclipse-workspace\CollectionTest\src\com\zyjhandsome\io\FileOutputStreamTest.java");
            fos = new FileOutputStream("D:\zhaoyingjun\else\Test\FileOutputStreamTest_copy2.java");
            while ((hasRead = fis.read(bbuf)) != -1)
            {
                fos.write(bbuf, 0, hasRead);
            }
            fis.close();
            fos.close();
        } catch (FileNotFoundException e2) {
            // TODO Auto-generated catch block
            e2.printStackTrace();
            System.out.println("系统找不到指定问你件");
            System.exit(-1);            
        }
        catch (IOException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
            System.out.println("文件复制错误");
            System.exit(-1);
        }
        System.out.println("文件已复制");        
    }
}

 　　如果希望直接输出字符串内容，则使用Writer会有更好的效果，如下程序所示：

package com.zyjhandsome.io;

import java.io.*;

public class FileWriterTest {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        try {
            FileWriter fw = new FileWriter("D:\User_zhaoyingjun\JavaSE\Test\FileWriterTest.txt");
            fw.write("锦瑟 - 李商隐
");
            fw.write("锦瑟无端五十弦，一弦一柱思华年。
");
            fw.write("庄生晓梦迷蝴蝶，望帝春心托杜鹃。
");
            fw.write("沧海月明珠有泪，蓝田日暖玉生烟。
");
            fw.write("此情可待成追忆，只是当时已惘然。
");
            fw.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }        
    }
}

 　　Windows平台，使用 换行；UNIX/Linux/BSD等平台，则使用 作为换行符号。