Java基础二十

1 转换流

1.1 转换流出现的原因

• 由于字节流操作中文的时候不是很方便，所以，Java就提供了转换流。
• 字符流=字节流+编码表。

1.2 String类的编码和解码功能

• 方法：通过指定的编码，将二进制的数据转换为字符串，即解码

String(byte[] bytes, Charset charset) 

• 方法：通过制定的编码，将字符串转换为二进制的数据，即编码

public byte[] getBytes(Charset charset)

• 示例：

package com.xuweiwei;

import java.io.UnsupportedEncodingException;

public class StringDemo {
    public static void main(String[] args) throws UnsupportedEncodingException {
        String str = "abcdef";

        //编码
        byte[] bytes = str.getBytes("UTF-8");

        for (byte aByte : bytes) {
            System.out.println("aByte = " + aByte +"、" );
        }



        //解码
        System.out.println("解码："+new String(bytes,"UTF-8"));
    }
}

2 OutputStreamWriter

• 作用：将字节输出流转换为字符输出流。

• 构造方法：根据指定的编码将字节流转换为字符流

public OutputStreamWriter(OutputStream out, String charsetName) throws UnsupportedEncodingException

• 示例：

package com.xuweiwei;

import java.io.*;

public class OutputStreamWriterDemo {
    public static void main(String[] args) throws IOException {
        Writer ow = new OutputStreamWriter(new FileOutputStream("ow.txt"),"utf-8");


        ow.write("你好，许威威");

        ow.close();


    }
}

3 InputStreamReader

• 将字节输入流转换为字符输入流

• 构造方法：

public InputStreamReader(InputStream in, String charsetName) throws UnsupportedEncodingException

• 示例：

package com.xuweiwei;


import java.io.*;

public class InputStreamReaderDemo {
    public static void main(String[] args) throws IOException {
        Reader reader = new InputStreamReader(new FileInputStream("ow.txt"),"utf-8");

        char[] buffer = new char[1024];
        
        int len = 0;

        while(-1 != (len = reader.read(buffer))){
            System.out.println(new String(buffer,0,len));
        }


        reader.close();
    }
}

4 转换流的简化写法

• 抓换流的名字比较长，而我们常见的操作都是按照本地默认编码实现的，所以， 为了简化我们的书写，转换流就提供了对应的子类。
• 例如：FileWriter和FileReader。

• 示例：

package com.xuweiwei;

import java.io.FileWriter;
import java.io.IOException;

public class FileWriterDemo {
    public static void main(String[] args) throws IOException {
        FileWriter fw = new FileWriter("fw.txt");

        fw.write("你好啊");

        fw.close();
    }
}

5 字符缓冲流

• BufferedWriter
  • 特殊功能：写一个行分隔符

public void newLine()   throws IOException

• BufferedReader
  • 特殊功能：读一个行分隔符　　

public String readLine()

• 示例：

package com.xuweiwei;

import java.io.*;

public class BufferedWriterDemo {
    public static void main(String[] args) throws IOException {
        BufferedWriter bw = new BufferedWriter(new FileWriter("bw.txt"));

        bw.write("你好啊");

        bw.flush();

        bw.close();


    }
}

• 示例：

package com.xuweiwei;

import java.io.FileWriter;
import java.io.IOException;

public class FileWriterDemo {
    public static void main(String[] args) throws IOException {
        FileWriter fw = new FileWriter("fw.txt");

        fw.write("你好啊");

        fw.close();
    }
}

• 示例：

package com.xuweiwei;

import java.io.*;

public class CopyDemo {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new FileReader("br.txt"));

        BufferedWriter bw = new BufferedWriter(new FileWriter("bw.txt"));

        String line = null;
        while(null != (line = br.readLine())){
            bw.write(line);
            bw.newLine();
            bw.flush();
        }

        bw.close();
        br.close();


    }
}