When should I use Java's StringWriter?

Question

What is a Java StringWriter, and when should I use it?

I have read the documentation and looked here, but I do not understand when I should use it.

Answer 1

It is a specialized Writer that writes characters to a StringBuffer, and then we use method like toString() to get the string result.

When StringWriter is used is that you want to write to a string, but the API is expecting a Writer or a Stream. It is a compromised, you use StringWriter only when you have to, since StringBuffer/StringBuilder to write characters is much more natural and easier,which should be your first choice.

Here is two of a typical good case to use StringWriter

1.Converts the stack trace into String, so that we can log it easily.

StringWriter sw = new StringWriter();//create a StringWriter
PrintWriter pw = new PrintWriter(sw);//create a PrintWriter using this string writer instance
t.printStackTrace(pw);//print the stack trace to the print writer(it wraps the string writer sw)
String s=sw.toString(); // we can now have the stack trace as a string

2.Another case will be when we need to copy from an InputStream to chars on a Writer so that we can get String later, using Apache commons IOUtils#copy :

StringWriter writer = new StringWriter();
IOUtils.copy(inputStream, writer, encoding);//copy the stream into the StringWriter
String result = writer.toString();