javaIO流

IO流结构图:

I O流的分类：

OutputStream(输出字节流)，InputStream(输入字节流).

Writer(输出字符流），Reader (输入字符流）.

 输出字节流OutputStream

 OutputStream是所有输出字节流的父类，它是一个抽象类，应该通过它的子类对象实例化.

范例: 向文件中写入字符串

class Hello{
public static void main(String[] arges){
            File file = new File("d:/a.txt");
            //覆盖原文件中数据
            OutputStream out = new FileOutputStream(file);
            //向原文件中追加数据
            //OutputStram out = new FileOutputStram(file,true);
            String str = "我不羡慕太阳 照不亮你的过往";
            out.write(str.getBytes());;
            out.close();
            
    }}
 }

  输入字节流: InputStream

 InputStream是所有输入流的父类，它是一个抽象类，应该通过它的子类对象实例化.

 范例: 字节流读取文件中内容

class Hello{
  public static void main(String[] arges){
     File file = new File("d:/a.txt");
         InputStream in = new FileInputStream(file);
         byte[] bytes = new byte[1024];
         int len = 0;
         while((len = in.read(bytes)) != -1)
         System.out.write(bytes, 0, len);
          in.close();

}
}

 范例: 复制文件

 class Hello {
    public static void main(String[] args) throws IOException {
        
        Hello file=new Hello();
        File srcFile=new File("d:/a.txt");
        File destFile=new File("d:/c.txt");
        file.CopyFile(srcFile,destFile);
    }
    public void CopyFile (File sourceFile,File destFile) throws IOException {
            InputStream in = new FileInputStream(sourceFile);
            OutputStream out = new FileOutputStream(destFile);
            byte []bytes = new byte[1024];
            int len=0;
            while((len= in.read(bytes)) != -1 ){
                    out.write(bytes,0,len);
            }
                    out.close();
                    in.close();    
    
    }
}

  Writer 输出字符流

  范例: 向文件中写入字符串

 class Hello {
    public static void main(String[] args) throws IOException {
        //File.separator代表系统目录中的间隔符
         File file = new File("d:"+File.separator+"a.txt");
         if(!file.getParentFile().exists()) {
             file.getParentFile().mkdir();//父目录必须存在
         }
         Writer out = new  FileWriter(file);
         String str = "Hello";
         out.write(str);
         out.append("World");//追加内容
         out.close();
         
    }

}

 Reder输入字符流

 范例:字符读取文件内容

 class Hello {
       public static void main(String[] args) throws IOException {
         File file = new File("d:"+File.separator+"a.txt");
         if(file.exists()) {
         Reader in = new FileReader(file);
         char [] data = new char[1024];
          int len = in.read(data);
          System.out.print(new String(data,0,len));
          in.close();     
    }

}
}

字节流与字符流的区别:字节流在进行处理的时候并不会用到缓冲区，而字符流会用到缓冲区（适用中文数据的处理）.

转换流: OutputStreamWriter和InputStreamReader

范例: 实现字符与字节之间的相互转换

     class Hello {
      public static void main(String[] args) throws IOException {
        File file = new File("d:"+File.separator+"a.txt"); 
        OutputStream output = new FileOutputStream(file);
        Writer out = new OutputStreamWriter(output)；
        InputStream  input = new FileInputStream(file);
        Reader in = new InputStreamReader(input);
        out.write("hello");
        in.read();
        out.close();
        in.close();
    }

}

内存操作流: ByteArrayInputStram和ByteArrayOutputStream

范例: 实现小写字母转大写字母

class Hello {

    public static void main(String[] args) throws IOException {
        String str = " hello";
        InputStream input = new ByteArrayInputStream(str.getBytes());
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        int data = 0;
        while((data=input.read()) != -1) {
            output.write(Character.toLowerCase(data));
        }
         byte[] result = output.toByteArray();
         System.out.println(new String (result));
        System.out.println(output);
        
        
    }

管道流: PipedOutputStream ，PipedInputStream(字节管道留) PipedReader ，PipedWriter(字符管道流)

范例:实现线程之间的信息传递

class SendThread implements Runnable{
 private PipedOutputStream output;
 public SendThread() {
      this.output = new PipedOutputStream(); 
 }
    @Override
    public void run() {
        for(int x = 0 ; x < 10 ; x++) {
            
            try {
                this.output.write(("【第"+(x+1)+Thread.currentThread().getName()+"发送消息】
").getBytes());
            } catch (IOException e) {
                
                e.printStackTrace();
            }
        
        }
        try {
            output.close();
        } catch (IOException e) {
            
            e.printStackTrace();
        }
    }
    public PipedOutputStream getOutput() {
        return output;
    }
     
 }
 class ReceiveThread implements Runnable{
    private PipedInputStream input;
    public ReceiveThread() {
        this.input = new PipedInputStream();
    }
    @Override
    public void run() {
        
            byte[]  data = new byte [1024];
            int len = 0;
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            try {
                while ((len = this.input.read(data)) != -1){
                    bos.write(data, 0 , len);
                }
                System.out.println(Thread.currentThread().getName()+"接收消息
"+new String (bos.toString()));
            } catch (IOException e) {
                
                e.printStackTrace();
            }
        
        try {
            this.input.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public PipedInputStream getInput() {
        return input;
    }
     
 }
 public class Hello {

    public static void main(String[] args) throws IOException {
        SendThread send = new SendThread();
        ReceiveThread receive = new ReceiveThread();
        send.getOutput().connect(receive.getInput());
        new Thread(send,"消息发送线程").start();
        new Thread(receive,"消息接收线程").start();   
    } 
 } 

RandomAccessFile(实现文件跳跃式读取)

前提: 需要有一个完整的保存形式

写入

 class Hello {

    public static void main(String[] args) throws IOException {
     File file = new File("d:"+File.separator+"a.txt");
     
     RandomAccessFile raf = new RandomAccessFile(file,"rw");
     String names [] = new String []{"zhangsan", "wangwu  ", "lisi    "};
     int ages [] = new int []{30,20,16};
     for(int x = 0; x < names.length; x ++ ) {
         raf.write(names[x].getBytes());
         raf.writeInt(ages[x]);
     }

     
    }
    
 }

读： 跳跃式读取一部分内容

class Hello {

    public static void main(String[] args) throws IOException {
     File file = new File("d:"+File.separator+"a.txt");
     RandomAccessFile raf = new RandomAccessFile(file,"rw");
       raf.skipBytes(24);
       byte [] data = new byte[8];
       int len = raf.read(data);
       System.out.println("姓名: " + new String (data, 0, len).trim() + "、年龄"+ raf.readInt());
     
    }
    
 }

 打印流:PrintSream与PrintWriter

范例：自己实现打印

class Hello {
    public static void main(String[] args) throws Exception {
        String dirPath = "/Users/fzc/Documents/mydir/mldn.txt";
        File file = new File(dirPath);
        PrintUtil util = new PrintUtil(new FileOutputStream(file));
        util.println("姓名：小强子");
        util.print("年龄：");
        util.print(78);
    }
}
class PrintUtil implements AutoCloseable {//实现数据常用的输出功能
    private OutputStream output;//不管现在如何进行输出操作，核心使用的就是OutputStream

    public PrintUtil(OutputStream output) {
        this.output = output;
    }

    public void print(String str) {//输出字符串
        try {
            this.output.write(str.getBytes());//输出
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public void println(String str) {
        this.print(str + "
");
    }
    public void print(long num) {
        this.print(String.valueOf(num));
    }
    public void println(long num) {
        this.println(String.valueOf(num));
    }
    @Override
    public void close() throws IOException {
        if (output != null) {
            output.close();
        }
    }
}

使用PrintWriter来实现数据的输出操作。
范例：数据输出

 class Hello {
    public static void main(String[] args) throws Exception {
        String dirPath = "/Users/fzc/Documents/mydir/mldn.txt";
        File file = new File(dirPath);
        PrintWriter util = new PrintWriter(new FileOutputStream(file));
        util.println("姓名：小强子");
        util.print("年龄：");
        util.print(78);
        util.close();
    }
}

 System类对IO的支持:

范例：实现键盘输入

class Hello {
    public static void main(String[] args) throws Exception {
        InputStream in=System.in;//此时的输入流为键盘输入
        System.out.print("请输入信息：");
        byte[] data=new byte[1024];//长度限制
        int len=in.read(data);
        System.out.println("输入的内容为："+new String(data,0,len));
        in.close();
        //请输入信息：asdasda
        //输入的内容为：asdasda
    }
}

 缓冲字输入符流 ：BufferedReader

范例：实现键盘数据输入

 class Hello{
    public static void main(String[] args) throws Exception {
        BufferedReader reader=new BufferedReader(new InputStreamReader(System.in));
        System.out.print("请输入信息：");
        String msg=reader.readLine();
        System.out.println("输入的内容为："+msg);
        reader.close();
        //请输入信息：123
        //输入的内容为：123
    }
}

范例：接收整型输入并且验证

class Hello{
    public static void main(String[] args) throws Exception {
        BufferedReader reader=new BufferedReader(new InputStreamReader(System.in));
        System.out.print("请输入您的年龄：");
        String msg=reader.readLine();
        if(msg.matches("\d{1,3}")){
            int age=Integer.valueOf(msg);
            System.out.println("您输入的年龄："+msg);
        }else{
            System.err.println("输入错误，你输入的内容："+msg);
        }
        reader.close();
    }
}

Scanner类

范例：使用Scanner读取文件信息

class Hello {
    public static void main(String[] args) throws Exception {
      //使用Scanner从文件读取内容(不能有空格,有空格不会读取完整)
        String dirPath = "/Users/fzc/Documents/mydir/mldn.txt";//定义操作的文件
        File file = new File(dirPath);
        Scanner sc = new Scanner(file);
        sc.useDelimiter("
");//默认以空格作为换行，设置以
为换行符
        while (sc.hasNext()) {
            System.out.println(sc.next());
        }
    }
}

 范例：输入一个人的生日

class Hello{
public static void main(String[] args) throws Exception {
        String birthdayRegex="\d{4}-\d{2}-\d{2}";
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入您的生日：");
        if (sc.hasNext(birthdayRegex)) {
            System.out.println("您输入的生日：" + sc.next());//换行不算输入
        } else {
            System.err.println("输入有误，未获取到内容");
        }
    }
}