Java 文件操作一（写文件、按行读文件、删除文件、复制文件、追加数据、创建临时文件、修改最后修改日期、获取文件大小）

文件写入

import java.io.*;
 
public class Main {
    public static void main(String[] args)  {
        try {
            BufferedWriter out = new BufferedWriter(new FileWriter("sanguo.txt"));
            out.write("三国教程");
            out.close();
            System.out.println("文件创建成功！");
        } catch (IOException e) {
        }
    }
}

以上代码运行输出结果为：

文件创建成功！

 

读取文件内容

import java.io.*;
 
public class Main {
    public static void main(String[] args)  {
        try {
            BufferedReader in = new BufferedReader(new FileReader("test.log"));
            String str;
            while ((str = in.readLine()) != null) {
                System.out.println(str);
            }
            System.out.println(str);
        } catch (IOException e) {
        }
    }
}

以上代码运行输出结果为：

111
222
333

 

删除文件

import java.io.*;
 
public class Main
{
    public static void main(String[] args)
    {
        try{
            File file = new File("c:\\test.txt");
            if(file.delete()){
                System.out.println(file.getName() + " 文件已被删除！");
            }else{
                System.out.println("文件删除失败！");
            }
        }catch(Exception e){
            e.printStackTrace();
        }
    }
}

以上代码运行输出结果为(需要在 C 盘上先创建 test.txt 文件)：

test.txt 文件已被删除！

 

将文件内容复制到另一个文件

import java.io.*;
 
public class Main {
    public static void main(String[] args) throws Exception {
        BufferedWriter out1 = new BufferedWriter(new FileWriter("srcfile"));
        out1.write("string to be copied\n");
        out1.close();
        InputStream in = new FileInputStream(new File("srcfile"));
        OutputStream out = new FileOutputStream
        (new File("destnfile"));
        byte[] buf = new byte[1024];
        int len;
        while ((len = in.read(buf)) > 0) {
            out.write(buf, 0, len);
        }
        in.close();
        out.close();
        BufferedReader in1 = new BufferedReader(new FileReader("destnfile"));
        String str;
        while ((str = in1.readLine()) != null) {
            System.out.println(str);
        }
        in1.close();
    }
}

以上代码运行输出结果为：

string to be copied

 

向文件中追加数据

import java.io.*;
 
public class Main {
    public static void main(String[] args) throws Exception {
        try {
            BufferedWriter out = new BufferedWriter(new FileWriter("filename"));
            out.write("aString1\n");
            out.close();
            out = new BufferedWriter(new FileWriter("filename",true));
            out.write("aString2");
            out.close();
            BufferedReader in = new BufferedReader(new FileReader("filename"));
            String str;
            while ((str = in.readLine()) != null) {
                System.out.println(str);
            }
            in.close();
        }
            catch (IOException e) {
            System.out.println("exception occoured"+ e);
        }
    }
}

以上代码运行输出结果为：

aString1
aString2

 

创建临时文件

//默认临时路径

import java.io.*;
 
public class Main {
    public static void main(String[] args) throws Exception {
        File temp = File.createTempFile("testrunoobtmp", ".txt");
        System.out.println("文件路径: "+temp.getAbsolutePath());
        temp.deleteOnExit();
        BufferedWriter out = new BufferedWriter(new FileWriter(temp));
        out.write("aString");
        System.out.println("临时文件已创建:");
        out.close();
    }
}

// 指定临时路径

import java.io.File;
 
public class Main {
 
   public static void main(String[] args) {      
      File f = null;
            
      try {
      
         // 创建临时文件
         f = File.createTempFile("tmp", ".txt", new File("C:/"));
         
         // 输出绝对路径
         System.out.println("File path: "+f.getAbsolutePath());
         
         // 终止后删除临时文件
         f.deleteOnExit();
         
         // 创建临时文件
         f = File.createTempFile("tmp", null, new File("D:/"));
         
         // 输出绝对路径
         System.out.print("File path: "+f.getAbsolutePath());
         
         // 终止后删除临时文件
         f.deleteOnExit();
         
      } catch(Exception e) {
      
         // 如果有错误输出内容
         e.printStackTrace();
      }
   }
}

 

修改文件最后的修改日期

import java.io.File;
import java.util.Date;
 
public class Main {
    public static void main(String[] args) throws Exception {
        File fileToChange = new File("C:/myjavafile.txt");
        fileToChange.createNewFile();
        Date filetime = new Date(fileToChange.lastModified());
        System.out.println(filetime.toString());
        System.out.println(fileToChange.setLastModified(System.currentTimeMillis()));
        filetime = new Date(fileToChange.lastModified());
        System.out.println(filetime.toString());
    }
}

以上代码运行输出结果为：

Sat Mar 21 22:00:48 CST 2015
true
Fri Apr 10 11:09:19 CST 2015

 

获取文件大小

import java.io.File;
 
public class Main {
    public static long getFileSize(String filename) {
        File file = new File(filename);
        if (!file.exists() || !file.isFile()) {
            System.out.println("文件不存在");
            return -1;
        }
        return file.length();
    }
    public static void main(String[] args) {
        long size = getFileSize("c:/java.txt");
        System.out.println("java.txt文件大小为: " + size);
    }
}

以上代码运行输出结果为（java.txt 文件位于 C 盘）：

java.txt文件大小为: 480

 

本文地址：https://blog.csdn.net/u012206617/article/details/107684484