Java IO（二）

常用类

1，节点流类型

访问文件

FileInputStream和FileOutputStream分别继承自OutputStream和OutputStream，用于向文件中输入和输出字节。

FileInputStream和FileOutputStream的构造方法：

FileInputStream:
FileInputStream(File file)
Creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system.
FileInputStream(FileDescriptor fdObj)
Creates a FileInputStream by using the file descriptor fdObj, which represents an existing connection to an actual file in the file system.
FileInputStream(String name)
Creates a FileInputStream by opening a connection to an actual file, the file named by the path name name in the file system.

OutputStream:
FileOutputStream(File file)
Creates a file output stream to write to the file represented by the specified File object.
FileOutputStream(File file, boolean append)
Creates a file output stream to write to the file represented by the specified File object.
FileOutputStream(FileDescriptor fdObj)
Creates a file output stream to write to the specified file descriptor, which represents an existing connection to an actual file in the file system.
FileOutputStream(String name)
Creates a file output stream to write to the file with the specified name.
FileOutputStream(String name, boolean append)
Creates a file output stream to write to the file with the specified name.

FileInputStream和FileOutputStream类支持其父类InputStream和OutputStream所提供的数据读写方法。

注意：

在实例化FileInputStream和FileOutputStream时要用ty-catch语句加以处理，因为可能抛出FileNotFoundException。

在读写数据时也要用try-catch语句加以处理，因为可能抛出IOException。

例子：

①，FileInputStream & FileOutputStream

FileInputStream:

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

public class Test {

    public static void main(String[] args) {
        int b = 0;
        FileInputStream fis = null;
        try {
            fis = new FileInputStream("d:\\share\\java\\io\\TestFileInputStream.java");
        } catch (FileNotFoundException e) {
            System.out.println("找不到指定文件");
            System.exit(-1);
        }

        try {
            long num = 0;
            while((b = fis.read()) != -1) {
                System.out.print((char)b);
                num++;
            }
            fis.close();
            System.out.println("共读取了" + num + "个字节");
        } catch (IOException e) {
            System.out.println("文件读取错误");
            System.exit(-1);
        }
    }

}

输出： 对于中文乱码，因为是一个字节一个字节的读取，所以只读取了半个中文

import java.io.*;
public class TestFileInputStream {
  public static void main(String[] args) {
    int b = 0;
    FileInputStream in = null;
    try {
      in = new FileInputStream("d:\\share\\java\\io\\TestFileInputStream.java");
    } catch (FileNotFoundException e) {
      System.out.println("ÕÒ²»µ½Ö¸¶¨Îļþ");
      System.exit(-1);
    }

    try {
      long num = 0;
      while((b=in.read())!=-1){
        System.out.print((char)b);
        num++;
      }
      in.close();
      System.out.println();
      System.out.println("¹²¶ÁÈ¡ÁË "+num+" ¸ö×Ö½Ú");
    } catch (IOException e1) {
      System.out.println("Îļþ¶ÁÈ¡´íÎó"); System.exit(-1);
    }
  }
}共读取了700个字节

FileOutputStream

    public static void main(String[] args) {
        int b = 0;
        FileInputStream fis = null;
        FileOutputStream fos = null;
        try {
            fis = new FileInputStream("d:/share/java/HelloWorld.java");
            fos = new FileOutputStream("d:/share/java/io/HW.java");//没有回自动新建一个文件
            while ((b = fis.read()) != -1) {
                fos.write(b);
            }
            fis.close();
            fos.close();
        } catch (FileNotFoundException e) {
            System.out.println("找不到指定的文件");
            System.exit(-1);
        } catch (IOException e) {
            System.out.println("文件复制错误");
            System.exit(-1);
        }
        System.out.println("文件已复制");
    }

②，FileReader & FileWriter

FileReader:

    public static void main(String[] args) {
        int c = 0;
        FileReader fr = null;
        try {
            fr = new FileReader("d:\\share\\java\\io\\TestFileReader.java");
            while((c = fr.read()) != -1) {
                System.out.print((char)c);
            }
            fr.close();
        } catch (FileNotFoundException e) {
            System.out.println("找不到指定文件");
        } catch (IOException e) {
            System.out.println("读取文件出错");
        }
    }

FileWriter（一）

    public static void main(String[] args) {
        FileWriter fw = null;
        try {
            fw = new FileWriter(new File("d:\\unicode.dat"));
            for(int i = 0; i <= 50000; i++) {//char最大为65535
                fw.write(i);
            }
            fw.close();
        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("文件写入错误");
            System.exit(-1);
        }
    }

结果：D盘中的unicode.dat文件中的内容：

FileWriter（二）

    public static void main(String[] args) throws Exception {
        FileReader fr = new FileReader("d:/java/io/TestFileWriter2.java");
        FileWriter fw = new FileWriter("d:/java/io/TestFileWriter2.bak");
        int b;
        while((b = fr.read()) != -1) {
            fw.write(b);
        }
        fr.close();
        fw.close();
    }