As HTML report generation from JUnit supprisingly appears to be an Ant
feature only (refer to an earlier post on this subject), I supply my
home brewed version of this as promised (my appologize for the long
listing :-)

Some of the code is based on ideas from junit-addons as documented in
the source. Writing a custom report is probably not done by the book
due to the very poor documentation and strange (and quite fat) API of
JUnit.

Disclaimer: It was written in a rush and can probably be improved in a
number of ways.

Usage:

  java HtmlTestReport /my/path/to/classes > test-report.html

Jacob

import java.io.File;
import java.io.IOException;
import java.util.Date;
import java.util.List;
import java.util.ArrayList;
import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;

import junit.framework.Test;
import junit.framework.TestSuite;
import junit.framework.TestResult;
import junit.framework.TestFailure;
import junit.framework.AssertionFailedError;
import junit.framework.TestListener;

/**
 * Class for creating a HTML JUnit test report.
 *
 * @author <a href="mailto:jacob.dreyer@geosoft.nospam">Jacob Dreyer</a>
 */
public final class HtmlTestReport implements TestListener
{
  /** Background color of header */
  private final String HEADER_COLOR = "\"#ccccff\"";

  /** Background color of report */
  private final String BACKGROUND_COLOR = "\"#ffffff\"";

  /** Background color of successful tests */
  private final String SUCCESS_COLOR = "\"#99ff99\"";

  /** Background color of failed tests */
  private final String FAILURE_COLOR = "\"#ff9999\"";

  /** Directory of source root */
  private final File sourceDirectory_;

  /** Directory of classes root */
  private final File classDirectory_;

  /** Overall start time for report generation */
  private long time0_;

  /** Start time for current test  */
  private long startTime_;

  /** Error message of current test */
  private StringBuffer message_;

  /** Total number of succeeding tests */
  private int nSuccess_ = 0;

  /** Total number of failed tests */
  private int nFailed_ = 0;

  /**
   * Create a HTML report instance. Typical usage:
   * <pre>
   *   File sourceDir = new File("/home/joe/dev/src");
   *   File classDir  = new File("/home/joe/dev/classes");
   *
   *   HtmlTestReport report = new HtmlTestReport(sourceDir, classDir);
   *   report.print();
   * </pre>
   * The HTML report is written to stdout and will typically be
   * redirected to a .html file.
   *
   * @param sourceDirectory  Root directory of source. If specified, it
   *                         will be used to create a link to the source
   *                         file of failing classes. May be null.
   * @param classDirectory   Root directory of classes.
   */
  public HtmlTestReport(File sourceDirectory, File classDirectory)
  {
    assert classDirectory != null : "Illegal class directory";

    sourceDirectory_ = sourceDirectory;
    classDirectory_  = classDirectory;

    time0_ = System.currentTimeMillis();
  }

  /**
   * Print the HTML report to standard out.
   */
  public void print()
  {
    try {
      // Extract the test suite
      TestSuite suite = HtmlTestReport.build(classDirectory_);

      // Print report header
      printHeader();

      // Loop through all the tests and make the report run the test
      // and capture the result
      for (int i = 0; i < suite.testCount(); i++) {
        Test test = suite.testAt(i);
        run(test);
      }

      // Print report footer
      printFooter();
    }
    catch (IOException exception) {
      exception.printStackTrace();
    }
  }

  /**
   * Convert the specified number of milliseconds into a readable
   * string in the form [nSeconds].[nMilliseconds]
   *
   * @param nMillis  Number of milliseconds to convert.
   * @return         String representation of the input.
   */
  private static String getTime(long nMillis)
  {
    assert nMillis >= 0 : "Illegal time specification";

    long nSeconds = nMillis / 1000;
    nMillis -= nSeconds * 1000;
    StringBuffer time = new StringBuffer();
    time.append(nSeconds);
    time.append('.');
    if (nMillis < 100) time.append('0');
    if (nMillis < 10) time.append('0');
    time.append(nMillis);

    return time.toString();
  }

  /**
   * Print the HTML report header.
   */
  private void printHeader()
  {
    System.out.println("<html>");
    System.out.println("<table" +
                       " cellpadding=\"5\"" +
                       " cellspacing=\"0\"" +
                       " bgcolor=" + BACKGROUND_COLOR +
                       " border=\"1\"" +
                       " width=\"100%\"" +
                       ">");
    System.out.println("  <tr>");
    System.out.println("    <td bgcolor=" + HEADER_COLOR + " colspan=2>" +
                       "<font size=+2>" +
                       "<b>Test</b>" +
                       "</font>" +
                       "</td>");
    System.out.println("    <td bgcolor=" + HEADER_COLOR + ">" +
                       "<font size=+2>" +
                       "<b>Time</b>" +
                       "</font>" +
                       "</td>");
    System.out.println("    <td align=\"right\" bgcolor=" + HEADER_COLOR + ">" +
                       "<font size=+2>" +
                       "<b>" + new Date() + "</b>" +
                       "</font>" +
                       "</td>");
    System.out.println("  </tr>");
  }

  /**
   * Print the HTML report footer.
   */
  private void printFooter()
  {
    int nTotal = nSuccess_ + nFailed_;

    String color = nFailed_ == 0 ? SUCCESS_COLOR : FAILURE_COLOR;

    System.out.println("  <tr>");
    System.out.println("    <td colspan=3> &nbsp; </td>");
    System.out.println("    <td bgcolor=" + color +  ">");

    System.out.println("      <table border=0 cellspacing=0 cellpadding=0>");

    System.out.println("        <tr>");
    System.out.println("        <td><font size=+0 face=\"helvetica\"><b>Failed</b></font></td>");
    System.out.println("        <td><font size=+0 face=\"courier\">" +
                       nFailed_ +
                       " (" + (double) nFailed_ / nTotal * 100.0 + "%)" +
                       "</font>" +
                       "</td>");
    System.out.println("        </tr>");

    System.out.println("        <tr>");
    System.out.println("        <td><font size=+0 face=\"helvetica\"><b>Success &nbsp; &nbsp; </b></font></td>");
    System.out.println("        <td><font size=+0 face=\"courier\">" +
                       nSuccess_ +
                       " (" + (double) nSuccess_ / nTotal * 100.0 + "%)" +
                       "</font>" +
                       "</td>");
    System.out.println("        </tr>");

    System.out.println("        <tr>");
    System.out.println("        <td><font size=+0 face=\"helvetica\"><b>Total</b></font></td>");
    System.out.println("        <td><font size=+0 face=\"courier\">" +
                       nTotal +
                       "</font>" +
                       "</td>");
    System.out.println("        </tr>");

    System.out.println("        <tr>");
    System.out.println("        <td><font size=+0 face=\"helvetica\"><b>Time</b></font></td>");
    System.out.println("        <td><font size=+0 face=\"courier\">" +
                       HtmlTestReport.getTime(System.currentTimeMillis() - time0_) +
                       "</td>");
    System.out.println("        </tr>");

    System.out.println("      </table>");
    System.out.println("    </td>");
    System.out.println("  </tr>");

    System.out.println("</table>");
    System.out.println("</html>");
  }

  /**
   * Run the specified test and capture the result in the report.
   *
   * @param test  Test to run.
   */
  private void run(Test test)
  {
    System.out.println("  <tr>");
    System.out.println("    <td colspan=4>" +
                       "<font face=\"courier\">" +
                       "<b>" + test.toString() + "</b>" +
                       "</font>" +
                       "</td>");
    System.out.println("  </tr>");

    TestResult result = new TestResult();
    result.addListener(this);

    test.run(result);
  }

  /**
   * Create an anchor tag from the specified class and file name.
   *
   * @param className  Fully specified class name of class to link to.
   * @param fileName   File where the class resides.
   * @param lineNo     Line number to scroll to (TODO: not currently used).
   * @return           Anchor string of the form "<a href='link'>file</a>".
   */
  private String toLink(String className, String fileName, int lineNo)
  {
    assert sourceDirectory_ != null : "Source not available";
    assert className        != null : "Missing class name";
    assert fileName         != null : "Missing file name";
    assert lineNo           >= 0    : "Illegal line number spcifier";

    String base        = sourceDirectory_.toString() + "/";
    String packageName = className.substring(0, className.lastIndexOf('.'));

    String link = "<a href=\"" +
                  base +
                  packageName.replace(".", "/") +
                  "/" +
                  fileName +
                  "\">" +
                  fileName + ":" + lineNo +
                  "</a>";

    return link;
  }

  /**
   * Add the appropriate report content for a starting test.
   * This method is called by JUnit when a test is about to start.
   *
   * @param test  Test that is about to start.
   */
  public void startTest(Test test)
  {
    assert test != null : "Test cannot be null";

    startTime_ = System.currentTimeMillis();
    message_ = new StringBuffer();

    String name = test.toString();
    String testName = name.substring(0, name.indexOf('('));

    System.out.println("  <tr>");
    System.out.println("    <td> &nbsp; &nbsp; </td>");
    System.out.println("    <td valign=\"top\"><font face=\"courier\"><b>" + testName +
                       "</b></font></td>");
  }

  /**
   * Add the appropriate report content for a failed test.
   * This method is called by JUnit when a test fails.
   *
   * @param test       Test that is failing.
   * @param throwable  Throwable indicating the failure
   */
  public void    addError(Test test, Throwable throwable)
  {
    assert test != null      : "Test cannot be null";
    assert throwable != null : "Exception must be specified for failing test";

    StackTraceElement stackTrace[] = throwable.getStackTrace();
    for (int i = 0; i < stackTrace.length; i++) {
      String className = stackTrace[i].getClassName();
      if (!className.startsWith("junit")) {
        message_.append(stackTrace[i].getClassName());
        message_.append(" ");
        if (sourceDirectory_ != null)
          message_.append(toLink(stackTrace[i].getClassName(),
                                 stackTrace[i].getFileName(),
                                 stackTrace[i].getLineNumber()));
        message_.append("<br>");
        break;
      }
    }

    message_.append(" &nbsp; &nbsp; " + throwable.getMessage());
  }

  /**
   * Add the appropriate report content for a failed test.
   * This method is called by JUnit when a test fails.
   *
   * @param test       Test that is failing.
   * @param throwable  Throwable indicating the failure
   */
  public void    addFailure(Test test, AssertionFailedError error)
  {
    assert test  != null : "Test cannot be null";
    assert error != null : "Exception must be specified for failing test";

    // Treat failures and errors the same
    addError(test, error);
  }

  /**
   * Add the appropriate report content for the end of a test.
   * This method is called by JUnit when a test is done.
   *
   * @param test       Test that is done.
   */
  public void endTest(Test test)
  {
    assert test != null : "Test cannot be null";

    // Compute the test duration
    long time = System.currentTimeMillis() - startTime_;

    System.out.println("    <td valign=\"top\"><font face=\"courier\"> " +
                       HtmlTestReport.getTime(time) +
                       "</font></td>");

    // Test was a success
    if (message_.length() ==  0) {
      nSuccess_++;
      System.out.println("    <td bgcolor=" + SUCCESS_COLOR +
                         "<font face=\"helvetica\"><b>Success</b></font></td>");
    }

    // Test failed
    else {
      nFailed_++;
      System.out.println("    <td bgcolor=" + FAILURE_COLOR + ">" +
                         message_.toString() +
                         "</td>");
    }

    System.out.println("  </tr>");
  }

  /**
   * Method for creating a test suite from all tests
   * found in the present directory and its sub directories.
   *
   * @param directory  Root directory for test search.
   * @return           Test suite compund of all tests found.
   */
  private static TestSuite build(File directory)
    throws IOException
  {
    assert directory != null : "Directory cannot be null";

    TestSuite suite = new TestSuite(directory.getName());

    // Get list of all classes in the path
    List<String> classNames = HtmlTestReport.getAllClasses(directory);

    for (String className : classNames) {
      try {
        Class clazz = Class.forName(className);

        // Filter out all non-test classes
        if (junit.framework.TestCase.class.isAssignableFrom(clazz)) {

          // Because a 'suite' method doesn't always exist in a TestCase,
          // we need to use the try/catch so that tests can also be
          // automatically extracted
          try {
            Method suiteMethod = clazz.getMethod("suite", new Class[0]);
            Test test = (Test) suiteMethod.invoke(null);
            suite.addTest(test);
          }
          catch (NoSuchMethodException exception) {
            suite.addTest(new TestSuite(clazz));
          }
          catch (IllegalAccessException exception) {
            exception.printStackTrace();
            // Ignore
          }
          catch (InvocationTargetException exception) {
            exception.printStackTrace();
            // Ignore
          }
        }
      }
      catch (ClassNotFoundException exception) {
        // Ignore
      }
    }

    return suite;
  }

  /**
   * Retrieve all classes from the specified path.
   *
   * @param root  Root of directory of where to search for classes.
   * @return      List of classes on the form "com.company.ClassName".
   */
  private static List<String> getAllClasses(File root)
    throws IOException
  {
    assert root != null : "Root cannot be null";

    // Prepare the return array
    List<String> classNames = new ArrayList<String>();

    // Get all classes recursively
    String path = root.getCanonicalPath();
    HtmlTestReport.getAllClasses(root, path.length() + 1, classNames);

    return classNames;
  }

  /**
   * Retrive all classes from the specified path.
   *
   * @param root          Root of directory of where to search for classes.
   * @param prefixLength  Index into root path name of path considered.
   * @param result        Array to add classes found
   */
  private static void getAllClasses(File root, int prefixLength,
                             List<String> result)
    throws IOException
  {
    assert root         != null : "Root cannot be null";
    assert prefixLength >= 0    : "Illegal index specifier";
    assert result       != null : "Missing return array";

    // Scan all entries in the directory
    for (File entry : root.listFiles()) {

      // If the entry is a directory, get classes recursively
      if (entry.isDirectory()) {
        if (entry.canRead())
          getAllClasses(entry, prefixLength, result);
      }

      // Entry is a file. Filter out non-classes and inner classes
      else {
        String path = entry.getPath();
        boolean isClass = path.endsWith(".class") && path.indexOf("$") < 0;
        if (isClass) {
          String name = entry.getCanonicalPath().substring(prefixLength);
          String className = name.replace(File.separatorChar, '.').
                             substring(0, name.length() - 6);
          result.add(className);
        }
      }
    }
  }

  /**
   * A JUnit HTML report generator. Typical usage:
   * <pre>
   *   java HtmlTestReport /home/joe/dev/classes > test.html
   * </pre>
   *
   * @param arguments  Comand line arguments.
   */
  public static void main(String[] arguments)
  {
    // Parse command line arguments
    if (arguments.length < 1 || arguments.length > 2) {
      System.err.println("Usage: HtmlTestReport classDir [sourceDir]");
    }

    File classDirectory = new File(arguments[0]);

    File sourceDirectory = null;
    if (arguments.length == 2)
      sourceDirectory = new File(arguments[1]);

    // Create a HTML report instance
    HtmlTestReport report = new HtmlTestReport(sourceDirectory,
                                               classDirectory);

    // Print report to standard out
    report.print();
  }
}