JAVA中文件的读写处理

１.用 InputStream & OutputStream 这两个基类来进行读写操作

InputStream 中的 FileInputStream 类似一个文件句柄，通过它来对文件进行操作，类似的，在

OutputStream 中我们有 FileOutputStream 这个对象。

用FileInputStream 来读取数据的常用方法是：

FileInputStream fstream = new FileInputStream(args[0]);

DataInputStream in = new DataInputStream(fstream);

用 in.readLine() 来得到数据，然后用 in.close() 关闭输入流。

用FileOutputStream 来写入数据的常用方法是：

FileOutputStream out out = new FileOutputStream("myfile.txt");

PrintStream p = new PrintStream( out );

用 p.println() 来写入数据，然后用 p.close() 关闭输入。

代码如下：

　　// FileInputDemo

// Demonstrates FileInputStream and DataInputStream

import java.io.*;

class FileInputDemo {

public static void main(String args[]) {

// args.length is equivalent to argc in C

if (args.length == 1) {

try {

// Open the file that is the first command line parameter

FileInputStream fstream = new FileInputStream(args[0]);

// Convert our input stream to a DataInputStream

DataInputStream in = new DataInputStream(fstream);

// Continue to read lines while there are still some left to read

while (in.available() !=0) {

// Print file line to screen

System.out.println (in.readLine());

}

in.close();

} catch (Exception e) {

System.err.println("File input error");

}

}

else

System.out.println("Invalid parameters");

}

}

// FileOutputDemo

// Demonstration of FileOutputStream and PrintStream classes

import java.io.*;

class FileOutputDemo

{

public static void main(String args[]) {

FileOutputStream out; // declare a file output object

PrintStream p; // declare a print stream object

try {

// connected to "myfile.txt"

out = new FileOutputStream("myfile.txt");

// Connect print stream to the output stream

p = new PrintStream( out );

p.println ("This is written to a file");

p.close();

} catch (Exception e) {

System.err.println ("Error writing to file");

}

}

}

２.JDK 1.1中，支持两个新的对象 Reader & Writer, 它们只能用来对文本文件进行操作，而

JDK1.1中的 InputStream & OutputStream 可以对文本文件或二进制文件进行操作。

用FileReader 来读取文件的常用方法是：

FileReader fr = new FileReader("mydata.txt");

BufferedReader br = new BufferedReader(fr);

用 br.readLing() 来读出数据，然后用br.close() 关闭缓存，用fr.close() 关闭文件。

用 FileWriter 来写入文件的常用方法是：

FileWriter fw = new FileWriter("mydata.txt");

PrintWriter out = new PrintWriter(fw);

在用out.print 或 out.println 来往文件中写入数据，out.print 和 out.println的唯一区别是后者写

入数据或会自动开一新行。写完后要记得 用out.close() 关闭输出，用fw.close() 关闭文件。

// FileReadTest.java

// User FileReader in JDK1.1 to read a file

import java.io.*;

class FileReadTest {

public static void main (String[] args) {

FileReadTest t = new FileReadTest();

t.readMyFile();

}

void readMyFile() {

String record = null;

int recCount = 0;

try {

FileReader fr = new FileReader("mydata.txt");

BufferedReader br = new BufferedReader(fr);

record = new String();

while ((record = br.readLine()) != null) {

recCount++;

System.out.println(recCount + ": " + record);

}

br.close();

fr.close();

} catch (IOException e) {

System.out.println("Uh oh, got an IOException error!");

e.printStackTrace();

}

}

}

// FileWriteTest.java

// User FileWriter in JDK1.1 to writer a file

import java.io.*;

class FileWriteTest {

public static void main (String[] args) {

FileWriteTest t = new FileWriteTest();

t.WriteMyFile();

}

void WriteMyFile() {

try {

FileWriter fw = new FileWriter("mydata.txt");

PrintWriter out = new PrintWriter(fw);

out.print(“hi,this will be wirte into the file!”);

out.close();

fw.close();

} catch (IOException e) {

System.out.println("Uh oh, got an IOException error!");

e.printStackTrace();

}

}

}