Java中的File操作总结

1.创建文件

import java.io.File;
import java.io.IOException;

public class CreateFileExample
{
    public static void main( String[] args )
    {
        try {

          File file = new File("c:\newfile.txt");
      //创建文件使用createNewFile()方法
          if (file.createNewFile()){
            System.out.println("File is created!");
          }else{
            System.out.println("File already exists.");
          }

        } catch (IOException e) {
          e.printStackTrace();
    }
    }
}

2.建立文件路径

import java.io.File;
import java.io.IOException;

public class FilePathExample1 {
    public static void main(String[] args) {
      try {

        String filename = "newFile.txt";
        String workingDirectory = System.getProperty("user.dir");

        //****************//

        String absoluteFilePath = "";

        //absoluteFilePath = workingDirectory + System.getProperty("file.separator") + filename;
        absoluteFilePath = workingDirectory + File.separator + filename;

        System.out.println("Final filepath : " + absoluteFilePath);

        //****************//

        File file = new File(absoluteFilePath);

        if (file.createNewFile()) {
            System.out.println("File is created!");
        } else {
            System.out.println("File is already existed!");
        }

      } catch (IOException e) {
        e.printStackTrace();
      }
    }
}

/////////////////////////////////////////////////////////////////
import java.io.File;
import java.io.IOException;

public class FilePathExample2 {
    public static void main(String[] args) {
      try {

        String filename = "newFile.txt";
        String workingDirectory = System.getProperty("user.dir");

        //****************//

        File file = new File(workingDirectory, filename);

        //****************//

        System.out.println("Final filepath : " + file.getAbsolutePath());
        if (file.createNewFile()) {
            System.out.println("File is created!");
        } else {
            System.out.println("File is already existed!");
        }

      } catch (IOException e) {
        e.printStackTrace();
      }
    }
}

3.设置文件权限

@检查文件权限是否设置

file.canExecute()
file.canWrite()
file.canRead()

@设置权限
- file.setExecutable(boolean)
- file.setReadable(boolean)
- file.setWritable(boolean)

代码演示：

package com.File;
import java.io.File;
import java.io.IOException;

public class FilePermissionExample
{
    public static void main( String[] args )
    {
        try {

        //1.未设置权限    
          File file = new File("D:\2.txt");

//        if(file.exists()){
//        System.out.println("是否可执行: " + file.canExecute());
//        System.out.println("是否可写 : " + file.canWrite());
//        System.out.println("是否可读 : " + file.canRead());
//        }
        //2.已设置权限
          file.setExecutable(false);
          file.setReadable(false);
          file.setWritable(false);

          System.out.println(" 是否可执行: " + file.canExecute());
          System.out.println("是否可写 : " + file.canWrite());
          System.out.println("是否可读  : " + file.canRead());

          if (file.createNewFile()){
            System.out.println("文件已创建!");
          }else{
            System.out.println("文件已存在");
          }

        } catch (IOException e) {
          e.printStackTrace();
        }
    }
}

4.读取文本内容的重要几个流

BufferedInputStream
FileInputStream
FileReader
BufferedReader
FileInputStream
DataInputStream

@.BufferedInputStream、 DataInputStream的使用

import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

public class BufferedInputStreamExample {

    public static void main(String[] args) {

        File file = new File("C:\testing.txt");
        FileInputStream fis = null;
        BufferedInputStream bis = null;
        DataInputStream dis = null;

        try {
            fis = new FileInputStream(file);

            bis = new BufferedInputStream(fis);
            dis = new DataInputStream(bis);

            while (dis.available() != 0) {
                System.out.println(dis.readLine());
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                fis.close();
                bis.close();
                dis.close();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }
    }
}

@ FileInputStream的使用

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
public class ReadFileExample {

    public static void main(String[] args) {

        File file = new File("C:/robots.txt");
        FileInputStream fis = null;

        try {
            fis = new FileInputStream(file);

            System.out.println("Total file size to read (in bytes) : "
                    + fis.available());

            int content;
            while ((content = fis.read()) != -1) {
                // convert to char and display it
                System.out.print((char) content);
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (fis != null)
                    fis.close();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }
    }
}

@BufferedReader的使用

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class ReadFileExample1 {

    private static final String FILENAME = "E:\test\filename.txt";

    public static void main(String[] args) {

        BufferedReader br = null;
        FileReader fr = null;

        try {

            //br = new BufferedReader(new FileReader(FILENAME));
            fr = new FileReader(FILENAME);
            br = new BufferedReader(fr);

            String sCurrentLine;

            while ((sCurrentLine = br.readLine()) != null) {
                System.out.println(sCurrentLine);
            }

        } catch (IOException e) {

            e.printStackTrace();

        } finally {

            try {

                if (br != null)
                    br.close();

                if (fr != null)
                    fr.close();

            } catch (IOException ex) {

                ex.printStackTrace();

            }

        }

    }

}
#################################################################
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class ReadFileExample2 {

    private static final String FILENAME = "E:\test\filename.txt";

    public static void main(String[] args) {

        try (BufferedReader br = new BufferedReader(new FileReader(FILENAME))) {

            String sCurrentLine;

            while ((sCurrentLine = br.readLine()) != null) {
                System.out.println(sCurrentLine);
            }

        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}
#################################################################

5.写入文本的几个重要的流

BufferedOutputStream
FileOutputStream
FileWriter
BufferedWriter
FileOutputStream
DataOutputStream

@FileOutputStream 的使用

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

public class WriteFileExample {
    public static void main(String[] args) {

        File file = new File("c:/newfile.txt");
        String content = "This is the text content";

        try (FileOutputStream fop = new FileOutputStream(file)) {

            // if file doesn't exists, then create it
            if (!file.exists()) {
                file.createNewFile();
            }

            // get the content in bytes
            byte[] contentInBytes = content.getBytes();

            fop.write(contentInBytes);
            fop.flush();
            fop.close();

            System.out.println("Done");

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

@BufferedWriter的使用


import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

public class WriteToFileExample2 {

    private static final String FILENAME = "E:\test\filename.txt";

    public static void main(String[] args) {

        try (BufferedWriter bw = new BufferedWriter(new FileWriter(FILENAME))) {

            String content = "This is the content to write into file
";

            bw.write(content);

            // no need to close it.
            //bw.close();

            System.out.println("Done");

        } catch (IOException e) {

            e.printStackTrace();

        }

    }

}

6.向文件中添加新的内容

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
public class AppendToFileExample {

    private static final String FILENAME = "E:\test\filename.txt";

    public static void main(String[] args) {

        BufferedWriter bw = null;
        FileWriter fw = null;

        try {

            String data = " This is new content";

            File file = new File(FILENAME);

            // if file doesnt exists, then create it
            if (!file.exists()) {
                file.createNewFile();
            }

            // true = append file
            fw = new FileWriter(file.getAbsoluteFile(), true);
            bw = new BufferedWriter(fw);

            bw.write(data);

            System.out.println("Done");

        } catch (IOException e) {

            e.printStackTrace();

        } finally {

            try {

                if (bw != null)
                    bw.close();

                if (fw != null)
                    fw.close();

            } catch (IOException ex) {

                ex.printStackTrace();

            }
        }

    }

}

7.删除文件

mport java.io.File;

public class DeleteFileExample
{
    public static void main(String[] args)
    {
        try{

            File file = new File("c:\logfile20100131.log");

            if(file.delete()){
                System.out.println(file.getName() + " is deleted!");
            }else{
                System.out.println("Delete operation is failed.");
            }

        }catch(Exception e){

            e.printStackTrace();

        }

    }
}

8.删除指定格式的所有文件

import java.io.*;

public class FileChecker {

   private static final String FILE_DIR = "c:\folder";
   private static final String FILE_TEXT_EXT = ".txt";

   public static void main(String args[]) {
    new FileChecker().deleteFile(FILE_DIR,FILE_TEXT_EXT);
   }

   public void deleteFile(String folder, String ext){

     GenericExtFilter filter = new GenericExtFilter(ext);
     File dir = new File(folder);

     //list out all the file name with .txt extension
     String[] list = dir.list(filter);

     if (list.length == 0) return;

     File fileDelete;

     for (String file : list){
    String temp = new StringBuffer(FILE_DIR)
                      .append(File.separator)
                      .append(file).toString();
        fileDelete = new File(temp);
        boolean isdeleted = fileDelete.delete();
        System.out.println("file : " + temp + " is deleted : " + isdeleted);
     }
   }

   //inner class, generic extension filter
   public class GenericExtFilter implements FilenameFilter {

       private String ext;

       public GenericExtFilter(String ext) {
         this.ext = ext;
       }

       public boolean accept(File dir, String name) {
         return (name.endsWith(ext));
       }
    }
}

9.查找以某种格式的所有文件

import java.io.*;

public class FindCertainExtension {

    private static final String FILE_DIR = "c:\folder";
    private static final String FILE_TEXT_EXT = ".jpg";

    public static void main(String args[]) {
        new FindCertainExtension().listFile(FILE_DIR, FILE_TEXT_EXT);
    }

    public void listFile(String folder, String ext) {

        GenericExtFilter filter = new GenericExtFilter(ext);

        File dir = new File(folder);

        if(dir.isDirectory()==false){
            System.out.println("Directory does not exists : " + FILE_DIR);
            return;
        }

        // list out all the file name and filter by the extension
        String[] list = dir.list(filter);

        if (list.length == 0) {
            System.out.println("no files end with : " + ext);
            return;
        }

        for (String file : list) {
            String temp = new StringBuffer(FILE_DIR).append(File.separator)
                    .append(file).toString();
            System.out.println("file : " + temp);
        }
    }

    // inner class, generic extension filter
    public class GenericExtFilter implements FilenameFilter {

        private String ext;

        public GenericExtFilter(String ext) {
            this.ext = ext;
        }

        public boolean accept(File dir, String name) {
            return (name.endsWith(ext));
        }
    }
}

10.修改文件名

import java.io.File;

public class RenameFileExample
{
    public static void main(String[] args)
    {

        File oldfile =new File("oldfile.txt");
        File newfile =new File("newfile.txt");

        if(oldfile.renameTo(newfile)){
            System.out.println("Rename succesful");
        }else{
            System.out.println("Rename failed");
        }

    }
}

11.复制文件内容

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class CopyFileExample
{
    public static void main(String[] args)
    {

        InputStream inStream = null;
    OutputStream outStream = null;

        try{

            File afile =new File("Afile.txt");
            File bfile =new File("Bfile.txt");

            inStream = new FileInputStream(afile);
            outStream = new FileOutputStream(bfile);

            byte[] buffer = new byte[1024];

            int length;
            //copy the file content in bytes
            while ((length = inStream.read(buffer)) > 0){

                outStream.write(buffer, 0, length);

            }

            inStream.close();
            outStream.close();

            System.out.println("File is copied successful!");

        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

12.将一个文件移到另一个目录

import java.io.File;

public class MoveFileExample
{
    public static void main(String[] args)
    {
        try{

           File afile =new File("C:\folderA\Afile.txt");

           if(afile.renameTo(new File("C:\folderB\" + afile.getName()))){
            System.out.println("File is moved successful!");
           }else{
            System.out.println("File is failed to move!");
           }

        }catch(Exception e){
            e.printStackTrace();
        }
    }
}

13.创建文件是添加日期

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class GetFileCreationDateExample
{
    public static void main(String[] args)
    {

        try{

            Process proc =
               Runtime.getRuntime().exec("cmd /c dir c:\logfile.log /tc");

            BufferedReader br =
               new BufferedReader(
                  new InputStreamReader(proc.getInputStream()));

            String data ="";

            //it's quite stupid but work
            for(int i=0; i<6; i++){
                data = br.readLine();
            }

            System.out.println("Extracted value : " + data);

            //split by space
            StringTokenizer st = new StringTokenizer(data);
            String date = st.nextToken();//Get date
            String time = st.nextToken();//Get time

            System.out.println("Creation Date  : " + date);
            System.out.println("Creation Time  : " + time);

        }catch(IOException e){

            e.printStackTrace();

        }

    }
}

14.获取文件被修改的日期

import java.io.File;
import java.text.SimpleDateFormat;

public class GetFileLastModifiedExample
{
    public static void main(String[] args)
    {
    File file = new File("c:\logfile.log");

    System.out.println("Before Format : " + file.lastModified());

    SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");

    System.out.println("After Format : " + sdf.format(file.lastModified()));
    }
}

15.修改文件日期

import java.io.File;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class ChangeFileLastModifiedExample
{
    public static void main(String[] args)
    {

        try{

            File file = new File("C:\logfile.log");

            //print the original last modified date
            SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
            System.out.println("Original Last Modified Date : "
                    + sdf.format(file.lastModified()));

            //set this date
            String newLastModified = "01/31/1998";

            //need convert the above date to milliseconds in long value
            Date newDate = sdf.parse(newLastModified);
            file.setLastModified(newDate.getTime());

            //print the latest last modified date
            System.out.println("Lastest Last Modified Date : "
                    + sdf.format(file.lastModified()));

        }catch(ParseException e){

            e.printStackTrace();

        }

    }
}

16.设置文件只能读

import java.io.File;
import java.io.IOException;

public class FileReadAttribute
{

    public static void main(String[] args) throws IOException
    {
        File file = new File("c:/file.txt");

        //mark this file as read only, since jdk 1.2
        file.setReadOnly();

        if(file.canWrite()){
             System.out.println("This file is writable");
        }else{
             System.out.println("This file is read only");
        }

        //revert the operation, mark this file as writable, since jdk 1.6
        file.setWritable(true);

        if(file.canWrite()){
             System.out.println("This file is writable");
        }else{
             System.out.println("This file is read only");
        }
    }
}

17.获取文件大小

import java.io.File;

public class FileSizeExample
{
    public static void main(String[] args)
    {
        File file =new File("c:\java_xml_logo.jpg");

        if(file.exists()){

            double bytes = file.length();
            double kilobytes = (bytes / 1024);
            double megabytes = (kilobytes / 1024);
            double gigabytes = (megabytes / 1024);
            double terabytes = (gigabytes / 1024);
            double petabytes = (terabytes / 1024);
            double exabytes = (petabytes / 1024);
            double zettabytes = (exabytes / 1024);
            double yottabytes = (zettabytes / 1024);

            System.out.println("bytes : " + bytes);
            System.out.println("kilobytes : " + kilobytes);
            System.out.println("megabytes : " + megabytes);
            System.out.println("gigabytes : " + gigabytes);
            System.out.println("terabytes : " + terabytes);
            System.out.println("petabytes : " + petabytes);
            System.out.println("exabytes : " + exabytes);
            System.out.println("zettabytes : " + zettabytes);
            System.out.println("yottabytes : " + yottabytes);
        }else{
             System.out.println("File does not exists!");
        }

    }
}

18.获取文件路径

import java.io.File;
import java.io.IOException;

public class AbsoluteFilePathExample
{
    public static void main(String[] args)
    {
        try{

            File temp = File.createTempFile("i-am-a-temp-file", ".tmp" );

            String absolutePath = temp.getAbsolutePath();
            System.out.println("File path : " + absolutePath);

            String filePath = absolutePath.
                     substring(0,absolutePath.lastIndexOf(File.separator));

            System.out.println("File path : " + filePath);

        }catch(IOException e){

            e.printStackTrace();

        }

    }
}

19.获取文件的总行数

import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.LineNumberReader;

public class LineNumberReaderExample
{
    public static void main(String[] args)
    {

        try{

            File file =new File("c:\ihave10lines.txt");

            if(file.exists()){

                FileReader fr = new FileReader(file);
                LineNumberReader lnr = new LineNumberReader(fr);

                int linenumber = 0;

                    while (lnr.readLine() != null){
                    linenumber++;
                    }

                    System.out.println("Total number of lines : " + linenumber);

                    lnr.close();


            }else{
                 System.out.println("File does not exists!");
            }

        }catch(IOException e){
            e.printStackTrace();
        }

    }
}

20.检查文件是否存在


import java.io.*;

public class FileChecker {

  public static void main(String args[]) {

      File f = new File("c:\mkyong.txt");

      if(f.exists()){
          System.out.println("File existed");
      }else{
          System.out.println("File not found!");
      }

  }

}

21.检查文件是否隐藏

import java.io.File;
import java.io.IOException;

public class FileHidden
{

    public static void main(String[] args) throws IOException
    {
        File file = new File("c:/hidden-file.txt");

        if(file.isHidden()){
            System.out.println("This file is hidden");
        }else{
            System.out.println("This file is not hidden");
        }
    }
}

22.读取文件为UTF-8的数据

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

public class test {
    public static void main(String[] args){

    try {
        File fileDir = new File("c:\temp\test.txt");

        BufferedReader in = new BufferedReader(
           new InputStreamReader(
                      new FileInputStream(fileDir), "UTF8"));

        String str;

        while ((str = in.readLine()) != null) {
            System.out.println(str);
        }

                in.close();
        }
        catch (UnsupportedEncodingException e)
        {
            System.out.println(e.getMessage());
        }
        catch (IOException e)
        {
            System.out.println(e.getMessage());
        }
        catch (Exception e)
        {
            System.out.println(e.getMessage());
        }
    }
}

23.向文件中写入UTF-8的数据

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
import java.io.Writer;

public class test {
    public static void main(String[] args){

      try {
        File fileDir = new File("c:\temp\test.txt");

        Writer out = new BufferedWriter(new OutputStreamWriter(
            new FileOutputStream(fileDir), "UTF8"));

        out.append("Website UTF-8").append("
");
        out.append("?? UTF-8").append("
");
        out.append("??????? UTF-8").append("
");

        out.flush();
        out.close();

        } 
       catch (UnsupportedEncodingException e) 
       {
        System.out.println(e.getMessage());
       } 
       catch (IOException e) 
       {
        System.out.println(e.getMessage());
        }
       catch (Exception e)
       {
        System.out.println(e.getMessage());
       } 
    }   
}

24.将文本内容复制给一个变量

import java.io.DataInputStream;
import java.io.FileInputStream;

public class App{

    public static void main (String args[]) {

    try{

             DataInputStream dis =
            new DataInputStream (
                 new FileInputStream ("c:\logging.log"));

         byte[] datainBytes = new byte[dis.available()];
         dis.readFully(datainBytes);
         dis.close();

         String content = new String(datainBytes, 0, datainBytes.length);

         System.out.println(content);

    }catch(Exception ex){
        ex.printStackTrace();
    }

  }
}

25.生成文件校验值

import java.io.FileInputStream;
import java.security.MessageDigest;

public class TestCheckSum {

  public static void main(String args[]) throws Exception {

    String datafile = "c:\INSTLOG.TXT";

    MessageDigest md = MessageDigest.getInstance("SHA1");
    FileInputStream fis = new FileInputStream(datafile);
    byte[] dataBytes = new byte[1024];

    int nread = 0;

    while ((nread = fis.read(dataBytes)) != -1) {
      md.update(dataBytes, 0, nread);
    };

    byte[] mdbytes = md.digest();

    //convert the byte to hex format
    StringBuffer sb = new StringBuffer("");
    for (int i = 0; i < mdbytes.length; i++) {
        sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16).substring(1));
    }

    System.out.println("Digest(in hex format):: " + sb.toString());

  }
}

26.将文件转换成字节数组

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class FileToArrayOfBytes {

    public static void main(String[] args) {

        try {

            // convert file to byte[]
            byte[] bFile = readBytesFromFile("C:\temp\testing1.txt");

            //java nio
            //byte[] bFile = Files.readAllBytes(new File("C:\temp\testing1.txt").toPath());
            //byte[] bFile = Files.readAllBytes(Paths.get("C:\temp\testing1.txt"));

            // save byte[] into a file
            Path path = Paths.get("C:	emp\test2.txt");
            Files.write(path, bFile);

            System.out.println("Done");

            //Print bytes[]
            for (int i = 0; i < bFile.length; i++) {
                System.out.print((char) bFile[i]);
            }

        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    private static byte[] readBytesFromFile(String filePath) {

        FileInputStream fileInputStream = null;
        byte[] bytesArray = null;

        try {

            File file = new File(filePath);
            bytesArray = new byte[(int) file.length()];

            //read file into bytes[]
            fileInputStream = new FileInputStream(file);
            fileInputStream.read(bytesArray);

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fileInputStream != null) {
                try {
                    fileInputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

        }

        return bytesArray;

    }

}

27.文件保存字节数组

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class ArrayOfBytesToFile {

    private static final String UPLOAD_FOLDER = "C:\temp\";

    public static void main(String[] args) {

        FileInputStream fileInputStream = null;

        try {

            File file = new File("C:\temp\testing1.txt");
            byte[] bFile = new byte[(int) file.length()];

            //read file into bytes[]
            fileInputStream = new FileInputStream(file);
            fileInputStream.read(bFile);

            //save bytes[] into a file
            writeBytesToFile(bFile, UPLOAD_FOLDER + "test1.txt");
            writeBytesToFileClassic(bFile, UPLOAD_FOLDER + "test2.txt");
            writeBytesToFileNio(bFile, UPLOAD_FOLDER + "test3.txt");

            System.out.println("Done");

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fileInputStream != null) {
                try {
                    fileInputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

        }
    }

    //Classic, < JDK7
    private static void writeBytesToFileClassic(byte[] bFile, String fileDest) {

        FileOutputStream fileOuputStream = null;

        try {
            fileOuputStream = new FileOutputStream(fileDest);
            fileOuputStream.write(bFile);

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fileOuputStream != null) {
                try {
                    fileOuputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

    //Since JDK 7 - try resources
    private static void writeBytesToFile(byte[] bFile, String fileDest) {

        try (FileOutputStream fileOuputStream = new FileOutputStream(fileDest)) {
            fileOuputStream.write(bFile);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    //Since JDK 7, NIO
    private static void writeBytesToFileNio(byte[] bFile, String fileDest) {

        try {
            Path path = Paths.get(fileDest);
            Files.write(path, bFile);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}

28.将字符串转换成InputStream

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

public class StringToInputStreamExample {
    public static void main(String[] args) throws IOException {
    String str = "This is a String ~ GoGoGo";

    // convert String into InputStream
    InputStream is = new ByteArrayInputStream(str.getBytes());

    // read it with BufferedReader
    BufferedReader br = new BufferedReader(new InputStreamReader(is));

    String line;
    while ((line = br.readLine()) != null) {
        System.out.println(line);
    }

    br.close();
   }
}

29.将InputStream转换为字符串

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

public class InputStreamToStringExample {

    public static void main(String[] args) throws IOException {

        // intilize an InputStream
        InputStream is =
                     new ByteArrayInputStream("file content..blah blah".getBytes());

        String result = getStringFromInputStream(is);

        System.out.println(result);
        System.out.println("Done");

    }

    // convert InputStream to String
    private static String getStringFromInputStream(InputStream is) {

        BufferedReader br = null;
        StringBuilder sb = new StringBuilder();

        String line;
        try {

            br = new BufferedReader(new InputStreamReader(is));
            while ((line = br.readLine()) != null) {
                sb.append(line);
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (br != null) {
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        return sb.toString();

    }

}

30.将文件转换为十六进制


import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintStream;

public class File2Hex
{
    public static void convertToHex(PrintStream out, File file) throws IOException {
    InputStream is = new FileInputStream(file);

    int bytesCounter =0;
    int value = 0;
    StringBuilder sbHex = new StringBuilder();
    StringBuilder sbText = new StringBuilder();
    StringBuilder sbResult = new StringBuilder();

    while ((value = is.read()) != -1) {
        //convert to hex value with "X" formatter
            sbHex.append(String.format("%02X ", value));

        //If the chracater is not convertable, just print a dot symbol "."
        if (!Character.isISOControl(value)) {
            sbText.append((char)value);
        }else {
            sbText.append(".");
        }

        //if 16 bytes are read, reset the counter,
            //clear the StringBuilder for formatting purpose only.
        if(bytesCounter==15){
            sbResult.append(sbHex).append("      ").append(sbText).append("
");
            sbHex.setLength(0);
            sbText.setLength(0);
            bytesCounter=0;
        }else{
            bytesCounter++;
        }
       }

    //if still got content
    if(bytesCounter!=0){
         //add spaces more formatting purpose only
        for(; bytesCounter<16; bytesCounter++){
        //1 character 3 spaces
        sbHex.append("   ");
        }
        sbResult.append(sbHex).append("      ").append(sbText).append("
");
        }

        out.print(sbResult);
        is.close();
  }

   public static void main(String[] args) throws IOException
   {
        //display output to console
        convertToHex(System.out, new File("c:/file.txt"));

        //write the output into a file
        convertToHex(new PrintStream("c:/file.hex"), new File("c:/file.txt"));
    }
}

31.File如何得到空闲磁盘空间


import java.io.File;

public class DiskSpaceDetail
{
    public static void main(String[] args)
    {
        File file = new File("c:");
        long totalSpace = file.getTotalSpace(); //total disk space in bytes.
        long usableSpace = file.getUsableSpace(); ///unallocated / free disk space in bytes.
        long freeSpace = file.getFreeSpace(); //unallocated / free disk space in bytes.

        System.out.println(" === Partition Detail ===");

        System.out.println(" === bytes ===");
        System.out.println("Total size : " + totalSpace + " bytes");
        System.out.println("Space free : " + usableSpace + " bytes");
        System.out.println("Space free : " + freeSpace + " bytes");

        System.out.println(" === mega bytes ===");
        System.out.println("Total size : " + totalSpace /1024 /1024 + " mb");
        System.out.println("Space free : " + usableSpace /1024 /1024 + " mb");
        System.out.println("Space free : " + freeSpace /1024 /1024 + " mb");
    }
}