Java基础之IO流

＃＃Java基础之IO流
IO流常用几个类的关系如下:

IO.JPG

字节流

字节输入流FileInputStream 读取文件用法实例

通过字输入流从D盘中dd.txt文件中读取文件内容,采用字节输入流,每次读取一个字节的方式
public class MyInputStreamDemo {

    public static void main(String[] args) throws Exception {
        //创建字节输入流
        FileInputStream fis = new FileInputStream("d:/dd.txt");
        int by;
        while ((by = fis.read()) != -1) {
            System.out.print((char) by);
        }
        fis.close();

    }

}

通过字节数组读取的方式如下

public class MyInputStreamDemo {

    public static void main(String[] args) throws Exception {
        //创建字节输入流
        FileInputStream fis = new FileInputStream("d:/dd.txt");

        //通过字节数组,每次读取一个字节数组的方式读取文件
        byte[] arr =new byte[1024];
        int len;
        while ((len = fis.read(arr))!=-1){
            String s = new String(arr,0,len);
            System.out.println(s);
        }
        //释放资源
        fis.close();
    }

}

字节输出流FileOutputStream 写文件用法实例
通过一个一个字节的方式读取

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

        //创建字节输出流,并且指向d盘中的aa.txt文件
        FileOutputStream fos = new FileOutputStream("d:/aa.txt");
        int num = 10000;
        //循环写num次'a'字符,并且通过System类来计算所耗时间
        long startTime = System.currentTimeMillis();
        for (int i = 0; i <num ; i++) {
            fos.write('a');
        }
        long endTime = System.currentTimeMillis();
        //释放资源
        fos.close();
    }

FileOutputStream输出流,还可以一次写一个字节数组

public static void main(String[] args) throws IOException {
     
        FileOutputStream fos= new FileOutputStream("d:/bb.txt");
        int num = 1000000;
        //循环向d盘的bb.txt写入num次字符串"helloworld"
        long startTime1 = System.currentTimeMillis();
        for (int i = 0; i <num/10 ; i++) {
            String s = "helloworld";
            fos1.write(s.getBytes());   //getBytes()可以把一个字符串转换为一个字节数组
        }
        long endTime1 = System.currentTimeMillis();
        System.out.println(endTime1 - startTime1);
        //释放资源
        fos.close();

    }

在实际开发中,为了提高效率,一般采用带有缓冲功能的BufferedInputStream和BufferedOutputStream

BufferedInputStrem常见用法如下
从文件中读取内容,并且复制到其他地方

一个字节一个字节读取实例,比如拷贝文件,从E盘将py.exe,拷贝到D盘,并且命名为:copypy.exe,实现代码如下:
 public static void main(String[] args) throws Exception {
        //创建带缓冲的字节输入流对象
        BufferedInputStream fis = new BufferedInputStream(new FileInputStream("E:/py.exe"));
        //创建带缓冲的字节输出流对象
        BufferedOutputStream fos = new BufferedOutputStream(new FileOutputStream("D:/copypy.exe"));
        int by;
        while ((by = fis.read()) != -1) {
            fos.write(by);
        }
        //释放资源
        fos.close();
        fis.close();
}

一个字节数组的方式操作,比如拷贝文件,从E盘将py.exe,拷贝到D盘,并且命名为:copypy.exe,实现代码如下:
 public static void main(String[] args) throws Exception {
        //创建带缓冲的字节输入流对象
        BufferedInputStream fis = new BufferedInputStream(new FileInputStream("E:/py.exe"));
        //创建带缓冲的字节输出流对象
        BufferedOutputStream fos = new BufferedOutputStream(new FileOutputStream("D:/copypy.exe"));
        byte[] arr = new byte[1024];    //一般采用1024的整数倍,根据计算机性能可以适当调整,一般一倍到8倍就可以了.
        int len;
        while ((len = fis.read(arr)) != -1) {
            fos.write(arr, 0, len); //没读取一个字节数组,就写一个字节数组
            fos.flush();    //刷新缓冲区,将文件写入到硬盘
        }
        //释放资源
        fos.close();
        fis.close();
}

字符流

InputStreamReader和OutputStreamWriter

//在采用GBk编码方式,通过字符输出流,向d盘test.txt文件写入内容,然后通过字符输入流读取文件内容,将读到的内容打印在控制台
public static void main(String[] args) throws Exception {
        //采用GBK的编码格式,创建字符输出流对象
        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(new FileOutputStream("d:/test.txt"), "GBK"); 

        String s = "你好,世界,Hello,World";
        outputStreamWriter.write(s);    //字符流中的write()方法,可以直接传入字符串
        outputStreamWriter.close();
        //采用GBK的编码格式,创建字符输入流对象
        InputStreamReader inputStreamReader = new InputStreamReader(new FileInputStream("d:/test.txt"), "GBK");

        //一个字节一个字节读取
        int by;
        while ((by = inputStreamReader.read())!=-1){
            System.out.print((char)by);   //读取一个字节,就输出一个字节
       }

        //一次读数组
        char[] chs = new char[1024];
        int len;
        while ((len = inputStreamReader.read(chs)) != -1) {
            System.out.print(new String(chs, 0, len));
        }
        inputStreamReader.close();

    }

InputStreamReader和OutputStreamWriter对应的子类分别为FileReader和FileWriter在windows中采用默认的GBK编码格式的时,可以使用FileReader和FileWriter创建字符流

读取D盘中的MyBufferedDemo.java文件,写入到E盘中,实现代码如下:
public static void main(String[] args) throws Exception{
        //创建字符输入流对象
        FileReader fileReader = new FileReader("D:\\MyBufferedDemo.java");
        //创建字符输出流对象
        FileWriter fileWriter = new FileWriter("E:\\MyBufferedDemocopy.java");
        //通过字符数组的方式,来实现
        char[] ch = new char[1024];
        int len;
        while ((len = fileReader.read(ch))!=-1){
            fileWriter.write(ch,0,len);
            fileWriter.flush();
        }
        //释放资源
        fileWriter.close();
        fileReader.close();

    }

在实际开发中,为了提高效率,一般采用带有缓冲功能的BufferedWriter和BufferedReader
这里两个类中有特殊于其他类的方法:readLine() 和 newLine()

//从d盘的ab.txt文件中读取内容,并写入到e盘中的ab.txt文件中
public static void main(String[] args) throws Exception {
            //创建字符输入流对象
            BufferedReader br = new BufferedReader(new FileReader("d:/ab.txt"));
            //创建字符输出流对象
            BufferedWriter bw = new BufferedWriter(new FileWriter("e:/ab.txt"));
            String line;
            while ((line = br.readLine()) != null) {
                bw.write(line);
                bw.newLine();   //跟据系统环境进行换行
                bw.flush();
            }
            //释放资源
            bw.close();
            br.close();
}

带有缓冲功能的,通过数组方式操作,拷贝文本文件,字符流BufferedReader,BufferedWriter和字节流BufferedInputStream,BufferedOutputStream,三种方式效率对比代码如下:

public static void main(String[] args) throws Exception {
        long start1 = System.currentTimeMillis();
        methods1();
        long end1 = System.currentTimeMillis();
        System.out.println("readLine:" + (end1 - start1));  //1128毫秒

        long start2 = System.currentTimeMillis();
        methods2();
        long end2 = System.currentTimeMillis();
        System.out.println("字符数组:" + (end2 - start2));  //563毫秒

        long start3 = System.currentTimeMillis();
        methods3();
        long end3 = System.currentTimeMillis();
        System.out.println("字节数组:" + (end3 - start3));  //267毫秒


    }

    //readLine
    private static void methods1() throws Exception {
            BufferedReader br = new BufferedReader(new FileReader("d:/ab.txt"));
            BufferedWriter bw = new BufferedWriter(new FileWriter("ab.txt"));
            String line;
            while ((line = br.readLine()) != null) {
                bw.write(line);
                bw.newLine();
                bw.flush();
            }
            bw.close();
            br.close();

    }

    //字符数组缓冲
    private static void methods2() throws Exception {
        BufferedReader br = new BufferedReader(new FileReader("d:/ab.txt"));
        BufferedWriter bw = new BufferedWriter(new FileWriter("ab2.txt"));
        char[] arr = new char[1024];
        int len;
        while ((len = br.read(arr))!=-1){
            bw.write(arr,0,len);
            bw.flush();
        }
        bw.close();
        br.close();

    }
    //字节数组缓冲
    private static void methods3() throws Exception {
        BufferedInputStream br = new BufferedInputStream(new FileInputStream("d:/ab.txt"));
        BufferedOutputStream bw = new BufferedOutputStream(new FileOutputStream("ab3.txt"));
        byte[] arr = new byte[1024];
        int len;
        while ((len = br.read(arr))!=-1){
            bw.write(arr,0,len);
            bw.flush();
        }
        bw.close();
        br.close();

    }