[ Java 常見問題 ] Get an OutputStream into a String

Source From Here
Question
What's the best way to pipe the output from an java.io.OutputStream to a String in Java?

I'm considering writing a class like this (untested):

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1. class StringOutputStream extends OutputStream {  
2.   
3.   StringBuilder mBuf;  
4.   
5.   public void write(int byte) throws IOException {  
6.     mBuf.append((char) byte);  
7.   }  
8.   
9.   public String getString() {  
10.     return mBuf.toString();  
11.   }  
12. }  

But is there a better way? I only want to run a test!

How-To
I would use a ByteArrayOutputStream. And on finish you can call:

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1. new String( baos.toByteArray(), codepage );  

or better

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1. baos.toString( codepage );  

For the String constructor the codepage can be a String or an instance of java.nio.charset.Charset. A possible value isjava.nio.charset.StandardCharsets.UTF_8. Below is sample code:

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1. package howto;  
2.   
3. import java.io.ByteArrayOutputStream;  
4. import java.io.PrintStream;  
5. import java.nio.charset.StandardCharsets;  
6.   
7. import flib.util.HexByteKit;  
8.   
9. public class OutputStreamToString {  
10.   
11.     public static void main(String[] args) throws Exception{  
12.         MyOutputStream myOS = new MyOutputStream();  
13.         PrintStream out = new PrintStream(myOS);  
14.         out.write("Hello".getBytes());  
15.         System.out.printf("\t[Info] %s\n", myOS.toString());  
16.         out.write("World".getBytes());  
17.         System.out.printf("\t[Info] %s\n", myOS.toString());  
18.         String bytesStr = "E4B8ADE69687"; // '中文' byte array in UTF-8 encoding        
19.         out.write(HexByteKit.Hex2Byte(bytesStr));  
20.         System.out.printf("\t[Info] %s\n", myOS.toString());  
21.         System.out.printf("\t[Info] %s\n", myOS.toString(StandardCharsets.UTF_8.toString()));  
22.     }  
23.   
24.     public static class MyOutputStream extends ByteArrayOutputStream  
25.     {         
26.         @Override  
27.         public void write(byte[] b, int off, int len)  
28.         {  
29.             System.out.printf("\t[Info] Reading:[ ");  
30.             for(int i=0; i"%02X ", b[i+off]);  
31.             System.out.println("]");  
32.             super.write(b, off, len);  
33.         }  
34.     }  
35. }  

Execution result:

[Info] Reading:[ 48 65 6C 6C 6F ] # 'H' with ASCII code as 48 in hex...
[Info] Hello
[Info] Reading:[ 57 6F 72 6C 64 ]
[Info] HelloWorld
[Info] Reading:[ E4 B8 AD E6 96 87 ]
[Info] HelloWorld中文
[Info] HelloWorld中文 # The default coding will be UTF-8