JAVA笔记25-IO流（3）-处理流举例

处理流类型：

1、缓冲流

例1：

import java.io.*;
public class TestBufferStream{
    public static void main(String args[]){
        try{
            FileInputStream fis = new FileInputStream("TestCopyByMyself.java");
            BufferedInputStream bis = new BufferedInputStream(fis);
            int c = 0 ;
            System.out.println((char)bis.read());
            System.out.println((char)bis.read());
            bis.mark(100);//做标记，没看懂API
            for(int i=0; i<=10&&(c=bis.read()) != -1; i++){
                System.out.print((char)c+" ");
            }
            System.out.println();
            bis.reset();//回到标记的位置
            for(int i=0; i<=10&&(c=bis.read()) != -1; i++){
                System.out.print((char)c+" ");
            }
            bis.close();
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

例2：BufferedWriter BufferedRead 应用非常普遍（记住）

import java.io.*;
public class TestBufferStream{
    public static void main(String args[]){
        try{
            BufferedWriter bw = new BufferedWriter(new FileWriter("TestCopyByMyself.java"));
            BufferedReader br = new BufferedReader(new FileReader("TestCopyByMyself.java"));
            String s = null ;
            for(int i=0; i<=100; i++){
                s = String.valueOf(Math.random());//返回字符串表示形式
                bw.write(s);
                bw.newLine();
            }
            bw.flush();
            while((s=br.readLine())!= null){
                System.out.println(s);
            }
            bw.close();
            br.close();
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

2、转换流（重要）

例1：

import java.io.*;
public class TestTransForm{
    public static void main(String args[]){
        try{
            OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("TestCopyByMyself.java"));
            osw.write("fgatwesdghruklotueo");
            System.out.println(osw.getEncoding());
            osw.close();
            osw = new OutputStreamWriter(new FileOutputStream("TestCopyByMyself.java",true),"ISO8859_1");//true是在原文件基础上追加，否则覆盖原内容
            //ISO8859_1是字符编码，默认编码GBK
            osw.write("fgatwesdghruklotueo");
            System.out.println(osw.getEncoding());
            osw.close();
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

例2、典型用法

import java.io.*;
public class Test{
    public static void main(String args[]){
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(isr);
        String s = null ;
        try{
            while((s = br.readLine())!=null){
                if(s.equalsIgnoreCase("exit"))
                    break;
                System.out.println(s.toUpperCase());
            }
            br.close();
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

3、数据流

例1

import java.io.*;
public class TestDataStream{
    public static void main(String args[]){
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        DataOutputStream dos = new DataOutputStream(baos);
        try{
            dos.writeDouble(Math.random());
            dos.writeBoolean(true);
            ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
            System.out.println(bais.available());//字节数=9
            DataInputStream dis = new DataInputStream(bais);
            System.out.println(dis.readDouble());
            System.out.println(dis.readBoolean());
            dos.close();
            dis.close();
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

输出：

9
0.5303779743857895
true

练习：自己读写文件，注意文件中显示的并非double+boolean

import java.io.*;
public class Test{
    public static void main(String [] args){
        String filename = "data.txt";
        try{
            DataOutputStream dos = new DataOutputStream(new FileOutputStream(filename));
            DataInputStream dis = new DataInputStream(new FileInputStream(filename));
            dos.writeDouble(6.7);
            dos.writeInt(3);
            System.out.println(dis.available());
            System.out.println(dis.readDouble());
            System.out.println(dis.readInt());
            dos.close();
            dis.close();
        }catch(IOException e){
            e.printStackTrace();
        }

    }
}

4、Print流

例1：

import java.io.*;
public class TestPrintStream{
    public static void main(String args[]){
        PrintStream ps = null ;
        try{
            FileOutputStream fos = new FileOutputStream("log.dat");
            ps = new PrintStream(fos);
        }catch(IOException e){
            e.printStackTrace();
        }
        if(ps!=null){
            System.setOut(ps);//System.out中的out默认是命令行，setOut可以改变out的值，这里out指向ps。
        }
        int ln = 1;
        for(char c=0;c<=6000;c++){
            System.out.print(c+" ");
            if(ln++>=10){
                System.out.println();
                ln = 1;
            }
        }
    }

}

例2：

import java.io.*;
//输入文件名，读该文件内容
public class TestPrintStream{
    public static void main(String args[]){
        if(args.length<=0)
            return;
        String filename = args[0];
        if(filename!=null){
            list(filename,System.out);
        }
    }
    public static void list(String f, PrintStream fs){
        try{
            BufferedReader br = new BufferedReader(new FileReader(f));
            String s = null;
            while((s = br.readLine())!=null){
                fs.println(s);
            }
            br.close();
        }catch(IOException e){
            fs.println("无法读取文件");
        }
    }
}

例3：日志

import java.io.*;
import java.util.*;
public class TestPrintStream{
    public static void main(String args[]){
        String s = null;
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        try{
            FileWriter fw = new FileWriter("logfile.log",true);
            PrintWriter log = new PrintWriter(fw);
            while((s = br.readLine())!=null){
                if(s.equalsIgnoreCase("exit"))
                    break;
                System.out.println(s.toUpperCase());
                log.println("-----");
                log.println(s.toUpperCase());
                log.flush();
            }
            log.println("==="+new Date()+"===");
            log.flush();
            log.close();
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

日志的另一种写法（by myself）：

import java.io.*;
import java.util.*;
public class Test{
    public static void main(String [] args){
        String filename = "log.txt" ;
        String line = null ;
        try{
            InputStreamReader fr = new InputStreamReader(System.in);
            BufferedReader br = new BufferedReader(fr);
            FileWriter fw = new FileWriter(filename);
            /*
            PrintWriter pw = new PrintWriter(fw);

            while((line = br.readLine()) != null){
                if(line.equalsIgnoreCase("exit")){
                    break;
                }
                pw.println(line);
            }
            pw.write("==="+new Date()+"===");
            pw.flush();
            pw.close();
            */
            BufferedWriter bw = new BufferedWriter(fw);
            while((line=br.readLine()) != null){
                if(line.equalsIgnoreCase("exit")){
                    break;
                }
                bw.write(line);
                bw.newLine();
            }
            bw.write("==="+new Date()+"===");
            bw.flush();
            bw.close();
        }catch(IOException e){
            e.printStackTrace();
        }

    }
}

5、Object流

直接将Object写入或读出。

必须实现seriallzable接口（序列化），是标记性接口，JDK控制序列化过程。

transient关键字修饰的成员变量在序列化时不考虑，即只写入其他三个，而忽略该成员变量。

externalizable接口（外部化），是seriallzable的子接口。此外还有两个方法，自己控制序列化过程。

例1：

import java.io.*;
public class Test{
    public static void main(String [] args){
        String filename = "obj.txt";
        Obj o = new Obj();
        try{
            FileOutputStream fos = new FileOutputStream(filename);
            ObjectOutputStream oos = new ObjectOutputStream(fos);
            oos.writeObject(o);
            oos.flush();
            oos.close();
            FileInputStream fis = new FileInputStream(filename);
            ObjectInputStream ois = new ObjectInputStream(fis);
            Obj obj = (Obj)ois.readObject();
            System.out.println(obj.a+" "+obj.b+" "+obj.c);
        }catch(IOException e){
            e.printStackTrace();
        }catch(ClassNotFoundException e){
            e.printStackTrace();
        }
    }
}

class Obj implements Serializable{
    int a = 1 ;
    String b = "good" ;
    transient int c = 9 ;
}

输出：

1 good 0

总结：