java之IO节点流示例，其他情况举一反三都是类似的

Posted 2022-11-30 小蜗牛爱远行

• I/O流的一般操作流程：

• 创建或者选择数据源

• 选择I/O流

• 创建操作对象

• 创建读取or存储的缓存区

• 具体操作，写入，读取，转换等等

• 出现乱码原因：字节转字符，字节数不够，导致乱码；编码不一致导致乱码

• 注意事项

  • FileInput/OutputStream最适合用于操作非文本文件（如图片、视频等）

  • FileReader/Writer最适合用于操作文本文件（如txt文件）

  • BufferStream可以加速节点流操作文件的速度

    * 抽象基类            节点流（文件流）     缓冲流
    字节流
    * InputStream      FileInputStream     BufferedInputStream
    * OutputStream     FileOutputStream    BufferedOutputStream
    字符流
    * Reader           FileReader          BufferedReader
    * Writer           FileWriter          BufferedWriter
    

  • 示例：文件<----->字节流：BufferedInputStream(new FileInputStream(src)) -----> ByteArrayOutputStream; ByteArrayInputStream ----> new BufferedOutputStream(new FileOutputStream(dest)

• 示例：

  /*
  *文件转字节流
  */
  public static byte[] fileToByteArray(String filePath)
          //create source
          File file = new File(filePath);
          //select stream
          InputStream is = null;
          ByteArrayOutputStream os = null;
          
          try 
              //create object
              is = new FileInputStream(file);
              os = new ByteArrayOutputStream();
              //create catch place
              byte[] flush = new byte[1024*10];
              //do something
              int len = -1;
              while ((len=is.read(flush))!=-1)
                  String str = new String(flush, 0, len);
                  os.write(str.getBytes());
              
              os.flush();
              return os.toByteArray();
           catch (FileNotFoundException e) 
              e.printStackTrace();
           catch (IOException e) 
              e.printStackTrace();
           finally 
              //先开后关
              try 
                  if (null != os)
                      is.close();
                  
                  
               catch (IOException e) 
                  e.printStackTrace();
              
              try 
                  if (null != is)
                      is.close();
                  
               catch (IOException e) 
                  e.printStackTrace();
              
          
          return null;
      
  

  /*
  *字节流转文件
  */
  public static boolean byteArrayToFile(byte[] bytesArray, String filePath)
          //create source
          File file = new File(filePath);
          //select stream
          ByteArrayInputStream is = null;
          FileOutputStream os = null;
          try 
              //create object
              is = new ByteArrayInputStream(bytesArray);
              os = new FileOutputStream(file);
              //create catch place
              byte[] flush = new byte[1024*10];
              //do something
              int len = -1;
              while ((len=is.read(flush))!=-1)
                  os.write(flush, 0, len);
              
              os.flush();
              return true;
           catch (FileNotFoundException e) 
              e.printStackTrace();
           catch (IOException e) 
              e.printStackTrace();
           finally 
              //先开后关
              try 
                  if (null != os)
                      is.close();
                  
  
               catch (IOException e) 
                  e.printStackTrace();
              
              try 
                  if (null != is)
                      is.close();
                  
               catch (IOException e) 
                  e.printStackTrace();
              
          
          return false;
      
  

  public static boolean byteArrayToFile(byte[] bytesArray, String filePath)
      //create source
      File file = new File(filePath);
      //select stream(高版本JDK，无需close，try会帮你执行close, 操作字节流使用BufferedI/O，大大提高性能)
      try (ByteArrayInputStream is = new ByteArrayInputStream(bytesArray); OutputStream os = new BufferedOutputStream(new FileOutputStream(file)))
          //create catch place
          byte[] flush = new byte[1024*10];
          int len = -1;
          while ((len=is.read(flush))!=-1)
              os.write(flush, 0, len);
          
          os.flush();
          return true;
       catch (FileNotFoundException e) 
          e.printStackTrace();
       catch (IOException e) 
          e.printStackTrace();
      
      return false;
  
  

• 字节流，字符流转换；页面源代码读取

import java.io.*;
import java.net.URL;

/**
 * @author yyds
 * 字符流转字节流
 *
 */
public class ConvertTest 
    public static void main(String[] args) 
        //操作system,,in和system.out
        try (
             // InputStreamReader isr = new InputStreamReader(System.in);
             //OutputStreamWriter osw = new OutputStreamWriter(System.out);
             BufferedReader isr = new BufferedReader(new InputStreamReader(System.in));
             BufferedWriter osw = new BufferedWriter(new OutputStreamWriter(System.out));
             BufferedReader is = new BufferedReader(new InputStreamReader(new URL("http://www.baidu.com").openStream(), "UTF-8"));
             BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("baidu.html"), "UTF-8"));
             ) 
                int temp;
                String temp2;
                String temp1;
                while ((temp=is.read())!=-1)
                    System.out.print((char) temp);
                    bw.write(temp);
                
                while ((temp1=is.readLine())!=null)
                    bw.write(temp1);
                    bw.newLine();
                
            bw.flush();
            while (!"exit".equals(temp2 = isr.readLine()))
                osw.write(temp2);
                osw.newLine();
                osw.flush();
              catch (IOException e) 
            System.out.println(e.toString());