Java学习笔记——File类之文件管理和读写操作、下载图片

时间：2022-03-29 21:40:14

Java学习笔记——File类之文件管理和读写操作、下载图片

File类的总结：

1.文件和文件夹的创建

2.文件的读取

3.文件的写入

4.文件的复制（字符流、字节流、处理流）

5.以图片地址下载图片

文件和文件夹

相关函数

 (boolean) mkdir() 创建此抽象路径名指定的目录
 (boolean) mkdirs() 创建此抽象路径名指定的目录，包括所有必需但不存在的父目录。

 (boolean) delete() 删除此抽象路径名表示的文件或目录

 (boolean) createNewFile() 当不存在此路径名指定名称的文件时，创建一个新的空文件。

 

创建文件

public static void NewFile(String pathString) {
    File file = new File(pathString);
    if (!file.exists()) {
      try {
        if (file.createNewFile()) {
          System.out.println("文件创建成功");
        }
      } catch (Exception e) {
        // TODO: handle exception
        e.printStackTrace();
      }
    } else {
      System.out.println("文件已存在");
    }
  }

创建文件夹

public static void NewFileBox(String pathString) {
    File file2 = new File(pathString);
    if (!file2.exists()) {
      if (file2.mkdirs()) {
        System.out.println("文件夹成功");
      }
    } else {
      System.out.println("文件夹存在");
      file2.delete();//销毁文件
    }
  }

应用：

public static void main(String[] args) {
    NewFile("test/file.txt");
    NewFileBox("test/a/a/a/a");
  }

Writer写入文件

用FileWriter写入文件

public  static void ForFileWriter(String string,String fileName) {
    File file = new File(fileName);
    try {
      FileWriter fWriter = new FileWriter(file);
      fWriter.write(string);
      fWriter.close();
    } catch (Exception e) {
      // TODO: handle exception
      e.printStackTrace();
    }
  }

用BufferedWriter写入文件

public static void ForBufferedWriter(String string,String desFile) {
    BufferedWriter bWriter = null;
    try {
      bWriter = new BufferedWriter(new FileWriter(new File(desFile)));
      bWriter.write(string.toString());
      bWriter.close();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

应用：

public static void main(String[] args) {
    ForFileWriter("用FileWriter写入文件", "test/writer1.txt");
    ForBufferedWriter("用BufferedWriter写入文件", "test/writer2.txt");
  }

Reader读取文件

用FileReader读取文件

public static void testReadByReader(String fileName){
    File file = new File(fileName);
    FileReader fis = null;
    try {
      fis =  new FileReader(file);
      char[] arr = new char[1024 * 1000 * 6];
      int len = fis.read(arr);
      String data = new String(arr, 0, len);
      fis.close();
      System.out.println(fileName+"中按FileReader读取的文件内容是：\n"+data);
    } catch (Exception e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
  }

用FileInputStream读取文件

public static void testReadByInputStream(String fileName){
    File file = new File(fileName);
    FileInputStream fis = null;
    try {
      fis =  new FileInputStream(file);
      byte[] arr = new byte[1024 * 1000 * 6];
      int len = fis.read(arr);
      String data = new String(arr, 0, len);
      fis.close();
      System.out.println(fileName+"中按FileInputStream读取的文件内容是：\n"+data);
    } catch (Exception e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
  }

用BufferedReader读取文件

public static void testReadByBufferedReader(String fileName) {
    BufferedReader bReader = null;
    String line = null;
    StringBuffer buffer = new StringBuffer();
    try {
      bReader =new BufferedReader(new FileReader(new File(fileName)));
      while ((line = bReader.readLine())!=null) {
        buffer.append(line).append("\n");
      }
    } catch (Exception e) {
      // TODO: handle exception
      e.printStackTrace();
    }
    System.out.println(fileName+"中按BufferedReader读取的文件内容是：\n"+buffer.toString());
  }

应用： 

public static void main(String[] args) {
    testReadByInputStream("res/我.txt");
    testReadByReader("res/我.txt");
    testReadByBufferedReader("res/我.txt");
  }

文件的复制操作

字符流复制

public static void FileCopy1(String readfile,String writeFile) {
    try {
      FileReader input = new FileReader(readfile);
      FileWriter output = new FileWriter(writeFile);
      int read = input.read();
      while ( read != -1 ) {
        output.write(read);
        read = input.read();
      }
      input.close();
      output.close();
    } catch (IOException e) {
      System.out.println(e);
    }
  }

字节流复制

public static void FileCopy2(String readfile,String writeFile) {
    try {
      FileInputStream input = new FileInputStream(readfile);
      FileOutputStream output = new FileOutputStream(writeFile);
      int read = input.read();
      while ( read != -1 ) {
        output.write(read);
        read = input.read();
      }
      input.close();
      output.close();
    } catch (IOException e) {
      System.out.println(e);
    }
  }

处理流复制

public static void FileCopy3(String readfile,String writeFile) {
    BufferedReader bReader = null;
    BufferedWriter bWriter = null;
    String line = null;
    try {
      bReader = new BufferedReader(new FileReader(new File(readfile)));
      bWriter = new BufferedWriter(new FileWriter(new File(writeFile)));
      while ((line = bReader.readLine())!=null) {
        bWriter.write(line);
        bWriter.newLine();
      }
      bWriter.close();
      bReader.close();
    } catch (Exception e) {
      // TODO: handle exception
      e.printStackTrace();
    }
  }

应用：

public static void main(String[] args) {
    FileCopy1("res/我.txt", "test/1.txt");
    FileCopy2("res/我.txt", "test/2.txt");
    FileCopy3("res/我.txt", "test/3.txt");
    FileCopy2("res/me.jpg", "test/33.jpg");
  }

以图片地址下载图片

读取给定图片文件的内容，用FileInputStream

public static byte[] mReaderPicture(String filePath) {
    byte[] arr = null;
    try {
      File file = new File(filePath);
      FileInputStream fReader = new FileInputStream(file);
      arr = new byte[1024*100];
      fReader.read(arr);
    } catch (Exception  e) {
      // TODO: handle exception
      e.printStackTrace();
    }
    return arr;
  }

根据byte数组，创建一张新图。

public static void mWriterPicture(String newFileName,byte[] b){
    try {
      File file = new File(newFileName);
      FileOutputStream fStream = new FileOutputStream(file);
      fStream.write(b);
      fStream.close();
      System.out.println("图片创建成功    "+b.length);
    } catch (Exception e) {
      // TODO: handle exception
    }
  }

获取指定网址的图片，返回其byte[]

public static byte[] mReaderPictureToInternet(String strUr1){
    byte[] imgData = null;
    URL url;
    try {
      url = new URL(strUr1);
      URLConnection connection = url.openConnection();
      int length = (int)connection.getContentLength();
      InputStream is = connection.getInputStream();
      if (length!=-1) {
        imgData = new byte[length];
        byte[] temp = new byte[500*1024];
        int readLen = 0;
        int destPos = 0;
        while ((readLen = is.read(temp))>0) {
          System.arraycopy(temp, 0, imgData, destPos, readLen);
          //arraycopy(Object src, int srcPos, Object dest, int destPos, int length)
          //从指定源数组中复制一个数组，复制从指定的位置开始，到目标数组的指定位置结束
          destPos+=readLen;
        }
      }
      return imgData;
    } catch (Exception e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    return imgData;
  }

直接获取指定网址的图片

public static void DownPictureToInternet(String filePath,String strUr1){
    try {
      URL url = new URL(strUr1);
      InputStream fStream = url.openConnection().getInputStream();
      int b = 0;
      FileOutputStream fos = new FileOutputStream(new File(filePath));
      while ((b=fStream.read())!=-1) {
        fos.write(b);
      }
      fStream.close();
      fos.close();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

应用：

public static void main(String[] args) {
    mWriterPicture("test/1.jpg", mReaderPicture("res/me.jpg"));
    mWriterPicture("test/2.jpg", mReaderPictureToInternet(
        "http://pic2.desk.chinaz.com/file/201209/7/qinghimingyue4_p.jpg"));
    DownPictureToInternet("test/下载.jpg",
      "http://img3.100bt.com/upload/ttq/20130205/1360069663700.jpg");
  }

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