javaIO学习笔记

 

一、执行基本的输入输出：

//file:IOApp.java
package test;

import java.io.*;

public class IOApp{
	public static void main(String args[]){
		byte buffer[] = new byte[255];
		System.out.println("/nTye a line of text:");
		try{
			System.in.read(buffer,0,255);
		}catch(Exception e){
			String err = e.toString();
			System.out.println(err);
		}
		System.out.println("/nThe line you typed was:");
		try{
			String inputStr = new String(buffer,"Default");
			System.out.println(inputStr);
		}catch(UnsupportedEncodingException e){
			System.out.println("e:" + e);
		}
	}
}

输出：

System.out.println("String");

输入：

System.in.read(buffer,0,255);

获取输入的字符串：

String inputStr = new String(buffer,"Default");

二、读取文本文件中的内容

//file:FileApp.java
package test;

import java.io.*;

public class FileApp{
	public static void main(String args[]){
		byte buffer[] = new byte[2056];
		try{
			FileInputStream fileIn = new FileInputStream("untitled-1.png");
			int bytes = fileIn.read(buffer,0,2056);
			try{
				String str = new String(buffer,0,bytes,"Default");
				System.out.println(str);
			}catch(UnsupportedEncodingException e){
				System.out.println("The encoding /"Default/" was not found:" + e);
			}
		}
		catch(Exception e){
			String err = e.toString();
			System.out.println(err);
		}
	}
}	

将数据读入缓冲：

FileInputStream fileIn = new FileInputStream("filename");
int bytes = fileIn.read(buffer,0,2056);

从缓冲中读出读入的数据：

String str = new String(buffer,0,bytes,"Default");

三、从输入设备读入一行文本并存入文件

//file:FileApp2.java

package test;

import java.io.*;

public class FileApp2{
	public static void main(String args[]){
		byte buffer[] = new byte[80];
		try{
			System.out.println("/nEnter a line to be saved to disk:");
			int bytes = System.in.read(buffer);
			FileOutputStream fileOut = new FileOutputStream("line.txt");
			fileOut.write(buffer,0,bytes);
		}catch(Exception e){
			String err = e.toString();
			System.out.println(err);
		}
	}
}		

输入：

int bytes = System.in.read(buffer);

将输入的文本存入文件：

FileOutputStream fileOut = new FileOutputStream("line.txt");
fileOut.write(buffer,0,bytes);

四、列出所有以.java结尾文件

//file:ListJava.java
package test;

import java.io.*;

public class ListJava extends Object{
	public static void main(String args[]){
		//Create a File instance for the current directory
		File currDir = new File("test");
		
		//Get a filtered list of the .java files in the current directory
		String[] javaFiles = currDir.list(new JavaFilter());
		
		//Print out the contents of the javaFiles array
		for(int i=0;i<javaFiles.length;i++){
			System.out.println(javaFiles[i]);
		}
	}
}

JavaFilter.java文件

//file:JavaFilter.java

package test;

import java.io.*;

//This class implements a filename filter that only allows
//file that ends with .java

public class JavaFilter extends Object implements FilenameFilter{
	public JavaFilter(){}
	public boolean accept(File dir,String name)
	{
		//Only return true for accept if the file ends with .java
		return name.endsWith(".java");
	}	
}

获取目录：

File currDir = new File("test");

将文件列表读入数组：

String[] javaFiles = currDir.list(new JavaFilter());

输出文件列表：

for(int i=0;i<javaFiles.length;i++){
	System.out.println(javaFiles[i]);
}

设定要列表文件的扩展名：
在JavaFilter类的accept方法中：

return endsWith(".java");

五、创建临时文件，并在退出进删除

//file:TestFile.java

package test;

import java.io.*;

public class TestFile {
	public static void main(String args[]) {
		try {
			File tempFile = File.createTempFile("test#imagebear", ".tmp");
			FileOutputStream fout = new FileOutputStream(tempFile);
			PrintStream out = new PrintStream(fout);
			out.println("Place this test string in the temp file");
			tempFile.deleteOnExit();
		} catch (IOException ioe) {
			System.out.println(
				"There was a problem creating/writing to the temp file");
			ioe.printStackTrace(System.err);
		}
		System.out.println(
			"Until you hit 'enter' there is a temp file on the system");
		try {
			System.in.read();
		} catch (IOException e) {
		}
		System.exit(0);
	}
}

创建临时文件：

File tempFile = File.createTempFile("test#imagebear",".tmp");
FileOutputStream fout = new FileOutputStream(tempFile);
PrintStream out = new PrintStream(fout);

退出时删除：

tempFile.deleteOnExit();

退出：

System.exit(0);

六、使用RandomAccessFile读取和显示文本文件内容

//file:FileApp3.java
package test;

import java.io.*;

public class FileApp3 {
	public static void main(String args[]) {
		try {
			RandomAccessFile file = new RandomAccessFile("test/FileApp3.java", "r");
			long filePointer = 0;
			long length = file.length();
			while (filePointer < length) {
				String s = file.readLine();
				System.out.println(s);
				filePointer = file.getFilePointer();
			}
		}catch(Exception e){
			String err = e.toString();
			System.out.println(err);
		}
	}
}

构造RandomAccessFile对象：

RandomAccessFile File = new RandomAccessFile("test/FileApp3.java","r");

初始化文件指针：

long filePointer = 0;

获取文件的长度：

long length = File.length();

读取并显示文件的内容：

while(filePointer < length){
	String s = File.readLine();
	System.out.println(s);
	filePointer = File.getFilePointer();
}

import java.io.*;
public class CharInput
{
     public static void main(String args[])
{
String s;
try
{
FileInputStream is=new FileInputStream("suoxin.txt"); //读出指定的文件，二进制流
InputStreamReader ir=new InputStreamReader(is);  //读取二进制格式，字符流
BufferedReader in =new BufferedReader(ir); //读取字符流，变成反冲字符流
while((s=in.readLine()) !=null) //以行读取
System.out.println("Read:" +s);
in.close();
}
catch(IOException e)
{
}
}
}

使用RandomAccessFile从输入设备读入一行文本并存入文件

import java.io.*;
public class RandomFileRW
{
  public static void main(String args[])
  {
	  StringBuffer buf=new StringBuffer();
	  char ch;
	 try
	 {
		while( (ch=(char)System.in.read()) !='/n')
		{
			buf.append( ch);
		}  //读写方式可以为"r" or "rw"
		RandomAccessFile myFileStream=new RandomAccessFile("Input.txt","rw");  
		myFileStream . seek(myFileStream.length()) ; //定为指针到文件尾
		myFileStream.writeBytes(buf.toString());  //将用户从键盘输入的内容添加到文件的尾部
		myFileStream.close(); 
	  }
	  catch(IOException e)
	  {
	  }
   }
}

可参阅 ttp://bbs.tech.ccidnet.com/read.php?tid=165580