String 与 InputStream 的互相转换

1. String --> InputStream
InputStream String2InputStream(String str){
    ByteArrayInputStream stream = new ByteArrayInputStream(str.getBytes());
    return stream;
}

2. InputStream --> String
String inputStream2String(InputStream is){
    BufferedReader in = new BufferedReader(new InputStreamReader(is));
    StringBuffer buffer = new StringBuffer();
    String line = "";
    while ((line = in.readLine()) != null){
      buffer.append(line);
    }
    return buffer.toString();
}

跟大家说一下，这样的InputStream需要从文本文件（即纯文本的数据文件）中读取内容，然后将它的内容读出到一个String对象中。下面直接给出代码：

ackage cn.jcourse.example.io;  

import java.io.BufferedReader;  
import java.io.IOException;  
import java.io.InputStream;  
import java.io.InputStreamReader;  
import java.util.Properties;  

public class StreamToString {  

public static void main(String[] args) {  
StreamToString sts = new StreamToString();  

/*
* Get input stream of our data file. This file can be in the root of
* you application folder or inside a jar file if the program is packed
* as a jar.
*/
InputStream is = sts.getClass().getResourceAsStream("/data.txt");  

/*
* Call the method to convert the stream to string
*/
System.out.println(sts.convertStreamToString(is));  
}  

public String convertStreamToString(InputStream is) {  
/*
* To convert the InputStream to String we use the BufferedReader.readLine()
* method. We iterate until the BufferedReader return null which means
* there's no more data to read. Each line will appended to a StringBuilder
* and returned as String.
*/
BufferedReader reader = new BufferedReader(new InputStreamReader(is));  
StringBuilder sb = new StringBuilder();  

String line = null;  
try {  
while ((line = reader.readLine()) != null) {  
sb.append(line + "\n");  
}  
} catch (IOException e) {  
e.printStackTrace();  
} finally {  
try {  
is.close();  
} catch (IOException e) {  
e.printStackTrace();  
}  
}  

return sb.toString();  
}  
}

如果大家学习过JavaIO部分的API，相信大家对上面的代码应该比较容易理解。我大致的讲解下，主要讲解convertStreamToString方法，它是主要的转换方法。我们首先将InputStream转换为BufferedReader对象，该对象用于读取文本。然后我们就一行行的读取文本数据并加入到StringBuilder中（这里也可以用StringBuffer对象）。这里主要主意的地方是while的结束条件是当读取到的字符串为null。然后在最后将StringBuilder对象转换为字符串返回回去。