Java I/O 操作示例

给出几个Java I/O 操作的示例代码。

创建文件或目录

import java.io.File;
import java.io.IOException;
public class TestFileIO {
    public static void main(String[] args) {
        File dir = new File("dir1");
        dir.mkdir();  //创建目录
        File file = new File(dir,"file1");  //目录加文件名
        File file2 = new File("dir1/file2");  //完整路径
        try {
            file.createNewFile();  //创建文件,若存在同名文件,不会覆盖
            file2.createNewFile();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

删除文件

import java.io.File;
public class TestFileIO {
    public static void main(String[] args) {
        File file = new File("dir1/file2");
        if (file.delete()){
            System.out.println(file.getName() + " is deleted!");
        }else {
            System.out.println("File is not deleted!");
        }
    }
}

向文件逐行写入内容(覆盖写）

1. FileOutputStream

   import java.io.*;
   public class TestFileIO {
       public static void main(String[] args) throws IOException {
           File fout = new File("dir1/file1");
           FileOutputStream fos = new FileOutputStream(fout);
           BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(fos));
           for (int i = 0; i < 10; i++){
               bw.write("something");
               bw.newLine();
           }
           bw.close();
       }
   }

2. FileWriter

   import java.io.*;
   public class TestFileIO {
       public static void main(String[] args) throws IOException {
           File fout = new File("dir1/file1");
           FileWriter fw = new FileWriter(fout);
           for (int i = 0; i < 10; i++){
               fw.write("something" + System.getProperty("line.separator"));
           }
           fw.close();
       }
   }

3. PrintWriter

   import java.io.*;
   public class TestFileIO {
       public static void main(String[] args) throws IOException {
           File fout = new File("dir1/file1");
           PrintWriter pw = new PrintWriter(new FileWriter(fout));
           for (int i = 0; i < 10; i++){
               pw.println("something");
           }
           pw.close();
       }
   }
   

4. OutputStreamWriter

   import java.io.*;
   public class TestFileIO {
       public static void main(String[] args) throws IOException {
           File fout = new File("dir1/file1");
           FileOutputStream fos = new FileOutputStream(fout);
           OutputStreamWriter osw = new OutputStreamWriter(fos);
           for (int i = 0; i < 10; i++) {
               osw.write("something" + System.getProperty("line.separator"));
           }
           osw.close();
       }
   }
   

注：
往文本文件里写内容用FileWriter即可，比较方便。但是如果要自己定义字符编号和byte-buffer大小的话就要用FileOutputStream。

PrintWriter跟FileWriter的主要区别是PrintWriter可以格式化输出。该类实现了PrintStream的所有print方法。

追加写

import java.io.*;
public class TestFileIO {
    public static void main(String[] args) throws IOException {
        File fout = new File("dir1/file1");
        FileOutputStream fos = new FileOutputStream(fout,true);  //跟覆盖写唯一的区别是这里加了个true参数。
        OutputStreamWriter osw = new OutputStreamWriter(fos);
        for (int i = 0; i < 10; i++) {
            osw.write("something" + System.getProperty("line.separator"));
        }
        osw.close();
    }
}

拷贝文件

import java.io.*;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
public class TestFileIO {
    public static void main(String[] args) throws IOException {
        Path sour = Paths.get("dir1/file1");
        Path des = Paths.get("dir1/file2");
        Files.copy(sour,des);   //Files.copy(a,b)。
    }
}

合并多个文件

读取多个文件的内容，写入一个文件。

import java.io.*;
/**
 * Created by lbd on 2017/1/13.
 */
public class MergeFiles {
    public static void main(String[] args) throws IOException {
        String sourceFile1Path = "dir1/file1";
        String sourceFile2Path = "dir1/file2";
        String mergedFilePath = "dir1/mergedFile.txt";
        File[] files = new File[2];
        files[0] = new File(sourceFile1Path);
        files[1] = new File(sourceFile2Path);
        File mergedFile = new File(mergedFilePath);
        mergeFiles(files,mergedFile);
    }
    public static void mergeFiles(File[] files,File mergedFile) throws IOException {
        FileWriter fw = new FileWriter(mergedFile,true);
        BufferedWriter bw = new BufferedWriter(fw);
        for (File f : files){
            System.out.println("merging: " + f.getName());
            FileReader fr = new FileReader(f);
            BufferedReader br = new BufferedReader(fr);
            String aLine;
            while ((aLine = br.readLine()) != null){
                bw.write(aLine);
                bw.newLine();
            }
            br.close();
        }
        bw.close();
    }
}

移动文件

调用的是File.renameTo()方法。

import java.io.*;
public class MoveFile {
    public static void main(String[] args) throws IOException {
        File f1 = new File("dir1/file1");
        File f2 = new File("dir1/dir2/file3");  //dir2目录必须存在,否则无法移动成功
        f1.renameTo(f2);
    }
}

对文件内容排序

file1内容如下：

dog 
cat
--windows
--kankan
pps
game
--annot be guaranteed 
as it is, generally speaking, 
--impossible to make any hard gu
arantees in the p
--resence of unsynchr

对行进行排序，以上面的文本为例，排序后arantees in the p应该在第一行

import java.io.*;
import java.util.ArrayList;
import java.util.Collections;
/**
 * Created by lbd on 2017/1/13.
 */
public class TestJavaIO {
    public static void main(String[] args) throws IOException {
        File fin = new File("file1");
        File fout = new File("file2");
        String s;
        FileWriter fw = new FileWriter(fout);
        FileReader fr = new FileReader(fin);
        BufferedReader br = new BufferedReader(fr);
        BufferedWriter bw = new BufferedWriter(fw);
        ArrayList al = new ArrayList<>();
        while ((s = br.readLine()) != null ){
            if (!s.trim().startsWith("-") && s.trim().length() > 0){
                al.add(s);
            }
        }
        Collections.sort(al);
        for (String line : al){
            bw.write(line);
            bw.newLine();
            bw.write("------------------------------");
            bw.newLine();
        }
        br.close();
        bw.close();
    }
}

file2内容如下：

arantees in the p
------------------------------
as it is, generally speaking, 
------------------------------
cat
------------------------------
dog 
------------------------------
game
------------------------------
pps
------------------------------

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