1、String –> InputStream
InputStrem is = new ByteArrayInputStream(str.getBytes());
or
ByteArrayInputStream stream
= new ByteArrayInputStream(str.getBytes());

 2、InputStream–>String

inputStream input;

StringBuffer out = new StringBuffer();
     byte[] b = new byte[4096];
     for (int n; (n = input.read(b)) != -1;) {
      out.append(new String(b, 0, n));
     }
out.toString();
3、Reader –>String
BufferedReader in = new BufferedReader(new InputStreamReader(is));
StringBuffer buffer = new StringBuffer();
String line = " ";
while ((line = in.readLine()) != null){
buffer.append(line);
}
return buffer.toString();

4、String–>Reader
Reader reader = null;
BufferedReader r = new BufferedReader(reader);
StringBuilder b = new StringBuilder();
String line;
while((line=r.readLine())!=null) {
b.append(line);
b.append(“\r\n”);
}
b.toString();

String 、InputStream、Reader 的转换