ExceptionのStacktTraceの文字列を取得したいとき〜

import java.io.*;

/**
 * StackTraceTest.java
 *
 *
 * Created: Fri Jan 17 13:30:33 2003
 *
 * @author nikunoki
 * @version
 */

public class StackTraceTest {
    public StackTraceTest() {}
    
    public static void main(String[] args) {

        try { 
            throw new Exception("test exception");
        } catch (Exception ex) {
            StringWriter sw = null;
            PrintWriter  pw = null;
            
            sw = new StringWriter();
            pw = new PrintWriter(sw);
            ex.printStackTrace(pw);
            String trace = sw.toString();

            System.out.println("ここから");
            System.out.println(trace);
            System.out.println("ここまで");
            
            try { 
                if ( sw != null ) {
                    sw.flush();
                    sw.close();
                } 
                if ( pw != null ) {
                    pw.flush();
                    pw.close();
                }
            } catch (IOException ignore){}
            
        }
    }
} // StackTraceTest