FileInputStream在使用完以后，不关闭流，想二次使用可以怎么操作？

• 2019 年 12 月 19 日
• 筆記

面试题

import java.io.FileInputStream;  import java.io.FileOutputStream;  import java.io.IOException;  import java.lang.reflect.Field;  import java.lang.reflect.InvocationTargetException;  import java.lang.reflect.Method;    /**   * FileInputStream在使用完以后，不关闭流，想二次使用可以怎么操作？   * @author dhb   */  public class FileInputStreamDemo {        public static void main(String[] args) throws IOException, NoSuchMethodException, InvocationTargetException, IllegalAccessException, NoSuchFieldException {          String parentPath = "";          String text1Path = parentPath + "text1.txt";          String text2Path = parentPath + "text2.txt";          String text3Path = parentPath + "text3.txt";            FileInputStream text1InputStream = new FileInputStream(text1Path);          FileOutputStream text2OutputStream = new FileOutputStream(text2Path);          FileOutputStream text3OutputStream = new FileOutputStream(text3Path);            int len;          byte[] bytes = new byte[1024];          while ((len = text1InputStream.read(bytes)) != -1) {              text2OutputStream.write(bytes, 0, len);          }          Class<? extends FileInputStream> inputStreamClass = text1InputStream.getClass();          Field fd = inputStreamClass.getDeclaredField("fd");          fd.setAccessible(true);          Object o = fd.get(text1InputStream);          System.out.println(o.hashCode());            if (text1InputStream.read() == -1) {              Method open0 = inputStreamClass.getDeclaredMethod("open0", String.class);              open0.setAccessible(true);              open0.invoke(text1InputStream, text1Path);          }          Object o1 = fd.get(text1InputStream);          System.out.println(o1.hashCode());            while ((len = text1InputStream.read(bytes)) != -1) {              text3OutputStream.write(bytes, 0, len);          }            text2OutputStream.flush();          text2OutputStream.close();            text3OutputStream.flush();          text3OutputStream.close();      }    }

open和read执行流程

总结

FileInputStream通过再次open能实现重读的原理是：底层代码重新打开了一次文件，返回文件描述符(Linux)或句柄，这个值存在FileInputStream中的一个类型为FileDescriptor的对象中，FileDescriptor的fd是文件描述符，handle是句柄