(Photo: The Surface by Daniel*1977)

URLEncoder.encode(String url) is deprecated.  Java wants you to use URLEncoder.encode(String url, String enc).  But what do you put for the encoding parameter?  I always forget which is the whole point of this post.

URLEncoder.encode(url, "UTF-8");

Also on Windows if you want you can do:

URLEncoder.encode(url, "Cp1252");

For further reading please see default encoding of a jvm.

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1. Encode URI

Resource bundles contain locale-specific objects. When your program needs a locale-specific resource, a String for example, your program can load it from the resource bundle that is appropriate for the current user’s locale. In this way, you can write program code that is largely independent of the user’s locale isolating most, if not all, of the locale-specific information in resource bundles.

This allows you to write programs that can:

• be easily localized, or translated, into different languages
• handle multiple locales at once
• be easily modified later to support even more locales

And from the MessageFormat JavaDoc:

MessageFormat provides a means to produce concatenated messages in a language-neutral way. Use this to construct messages displayed for end users.

MessageFormat takes a set of objects, formats them, then inserts the formatted strings into the pattern at the appropriate places.

This is an example of an error message resource bundle, ErrorMessagesResources.properties.

userAlreadyExists=A user already exists with the name {0}.
passwordInvalid=Please enter a valid password.

This is an example of how you would use this resource bundle.

protected static final ResourceBundle resourceBundle =
    ResourceBundle.getBundle("com.betweengo.ErrorMessageResources");

public boolean handleLogin(DynamoHttpServletRequest pReq, DynamoHttpServletResponse pRes) {

  ...

  // user already exists
  String errMsg1 = resourceBundle.getString("userAlreadyExists");
  errMsg1 = MessageFormat.format(errMsg1, userName);

  ...

  // password invalid
  String errMsg2 = resourceBundle.getString("passwordInvalid");

  ...
}

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Enums are highly useful data types introduced in Java SE 5.0.  Though I love using them I often forget the exact syntax so this post is to remind me later how to use it.

public enum Example {
  FOO,BAR
}

// create one using its name
Example myExample = Example.valueOf(“bar”.toUpperCase());

// if statement
if (myExample == Example.FOO) System.out.println(“FOO!”);

// switch statement
switch (myExample) {
  case FOO: System.out.println(“FOO!”);
  case BAR: System.out.println(“BAR!”);
}

// output as String using name
System.out.println(myExample.name());

For further reading please see Java’s Enums guide and Enum Types (The Java™ Tutorials > Learning the Java Language > Classes and Objects).

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import java.lang.management.ManagementFactory;
import java.lang.management.ThreadInfo;
import java.lang.management.ThreadMXBean;

import junit.framework.TestCase;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.log4j.Appender;
import org.apache.log4j.Logger;

/**
 * Unit test for the ThrottlingFilter in a multi-threaded environment
 */
public class ThrottlingFilterThreadUTest extends TestCase {

  private static final Log logger = LogFactory.getLog(ThrottlingFilterThreadUTest.class);

  private static ThreadMXBean threadMXBean;

  @Override
  protected void setUp() throws Exception {
    super.setUp();
    threadMXBean = ManagementFactory.getThreadMXBean();
    logger.info("Thread contention monitoring supported: "
        + threadMXBean.isThreadContentionMonitoringSupported());
    logger.info("Thread contention monitoring enabled: "
        + threadMXBean.isThreadContentionMonitoringEnabled());
    threadMXBean.setThreadContentionMonitoringEnabled(true);
    logger.info("Thread contention monitoring enabled: "
        + threadMXBean.isThreadContentionMonitoringEnabled());
  }

  /**
   * Tests multiple threads using the same filter instance at the same time
   */
  public void testThreads() {
    Logger rootLogger = Logger.getRootLogger();
    assertNotNull(rootLogger);
    Appender fileAppender = rootLogger.getAppender("FILE");
    assertNotNull(fileAppender);
    ThrottlingFilter throttlingFilter = (ThrottlingFilter) fileAppender.getFilter();
    assertNotNull(throttlingFilter);

    ThreadGroup infoThreadGroup = new ThreadGroup("info-group");
    ThreadGroup errorThreadGroup = new ThreadGroup("error-group");
    Thread errorThread1 = new ErrorThread(errorThreadGroup, "error-thread-1");
    Thread infoThread1 = new InfoThread(infoThreadGroup, "info-thread-1");
    Thread errorThread2 = new ErrorThread(errorThreadGroup, "error-thread-2");
    Thread infoThread2 = new InfoThread(infoThreadGroup, "info-thread-2");
    infoThread1.start();
    errorThread1.start();
    errorThread2.start();
    infoThread2.start();

    while (true) {
      ThreadInfo[] threadInfos = threadMXBean.getThreadInfo(threadMXBean.getAllThreadIds());
      for (int i = 0; i < threadInfos.length; i++) {
        ThreadInfo threadInfo = threadInfos[i];
        if (threadInfo != null && threadInfo.getThreadState() == Thread.State.BLOCKED) {
          System.out.println("Thread '" + threadInfo.getThreadName()
              + "' is blocked on the monitor lock '" + threadInfo.getLockName()
              + "' held by thread '" + threadInfo.getLockOwnerName() + "'");
        }
      }

      if (!infoThread1.isAlive() && !errorThread1.isAlive() && !infoThread2.isAlive()
          && !errorThread2.isAlive())
        break;
    }
  }

  public static class ErrorThread extends Thread {

    private static final Log logger = LogFactory.getLog(ErrorThread.class);

    public ErrorThread(ThreadGroup tg, String name) {
      super(tg, name);
    }

    public void run() {
      for (int i = 0; i < 10; i++) {
        try {
          test(0);
        } catch (Exception e) {
          long start = System.currentTimeMillis();
          logger.error("Error!", e);
          long end = System.currentTimeMillis();
          System.out.println("Took " + (end-start) + "ms to log error");
        }
      }
    }

    // simulate large stack traces
    private void test(int i) {
      if (i >= 500)
        throw new RuntimeException("D'OH!");
      test(i+1);
    }
  }

  public static class InfoThread extends Thread {

    private static final Log logger = LogFactory.getLog(InfoThread.class);

    public InfoThread(ThreadGroup tg, String name) {
      super(tg, name);
    }

    public void run() {
      for (int i = 0; i < 100; i++) {
        logger.info("Hi!");
      }
    }
  }
}

The log4j.xml test file.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/"
    debug="false">

    <!-- ================================= -->
    <!--           Appenders               -->
    <!-- ================================= -->

    <!-- A time/date based rolling file appender -->
    <appender name="FILE"
        class="org.apache.log4j.DailyRollingFileAppender">
        <param name="File" value="server.log" />
        <param name="Append" value="true" />

        <!-- Rollover at midnight each day -->
        <param name="DatePattern" value="'.'yyyy-MM-dd" />

        <layout class="org.apache.log4j.PatternLayout">
            <!-- The default pattern: Date Priority [Category] Message\n -->
            <param name="ConversionPattern" value="%d %-5p [%c] %m%n" />
        </layout>

        <filter class="com.betweengo.log4j.ThrottlingFilter">
          <param name="maxCountSameMessage" value="100"/>
          <param name="maxCountSavedMessages" value="100"/>
          <param name="waitInterval" value="60"/>
        </filter>
    </appender>

    <!-- ======================= -->
    <!-- Setup the Root category -->
    <!-- ======================= -->

    <root>
        <level value="INFO" />
        <appender-ref ref="FILE" />
    </root>

</log4j:configuration>

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String encodedUri;
  try {
    encodedUri = URLEncoder.encode(uri, "UTF-8");
  }
  catch (UnsupportedEncodingException exc) {
    // this should never happen
    logger.warn("UTF-8 is not a supported encoding?  Not encoding for now...", exc);
    encodedUri = uri;
  }

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For example:

    // sleep the filter's wait interval
    try {
      Thread.sleep(filter.getWaitInterval() * 1000);
    }
    catch (InterruptedException exc) {
      logger.error("unexpected interrupt", exc);
    }

Sun has a tutorial calling Pausing Execution with Sleep.

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Traditionally, programmers think that when they execute a return statement they immediately leave the method they are executing.  In Java, this is no longer true with the usage of finally…

To avoid this pitfall, be sure you do not issue a return, break or continue statement inside of a try block. If you cannot avoid this, be sure the existence of a finally does not change the return value of the method. This particular problem can arise during maintenance of your code, even with careful design and implementation. Good comments and careful code reviews ward it off.

Practical Java Programming Language … – Google Book Search

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The javadoc of URL.equals says: “Since hosts comparison requires name resolution, this operation is a blocking operation.”, but who reads the documentation of equals?  There is a general contract around equals.  Joshua Bloch writes in Effective Java: “Don’t write an equals that relies on unreliable resources” (Chapter 3, page 34). Hey Sun, as far as I know, the Internet is not reliable

Eclipse and Java Blog by Michael Scharf: java.net.URL.equals and hashCode make (blocking) Internet connections….

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However for some unknown reason in ServletException the getRootCause() method was added.  Therefore when trying to determine the root cause of an exception in a J2EE environment one has to check what type of exception you have.  I do this in the following code.

  /**
   * Logs all the nested exceptions for the specified exception.
   *
   * @param ex the exception
   */
  protected void logNestedExceptions(Throwable ex) {
    int count = 1;
    Throwable cause = getCause(ex);
    while (cause != null) {
      logger.error("Nested Exception " + count, cause);
      cause = getCause(cause);
      count++;
    }
  }

  /**
   * Gets the cause of the exception.
   *
   * @param ex the exception
   * @return the cause
   */
  protected Throwable getCause(Throwable ex) {
    Throwable cause;
    if (ex instanceof ServletException) {
      ServletException sex = (ServletException) ex;
      cause = sex.getRootCause();
    }
    else {
      cause = ex.getCause();
    }
    return cause;
  }

Finally you need to configure web.xml to use your SiteMap servlet.

<servlet>
    <servlet-name>sitemap</servlet-name>
    <servlet-class>com.betweengo.servlet.SiteMap</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>sitemap</servlet-name>
    <url-pattern>/sitemap.xml</url-pattern>
</servlet-mapping>

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  protected static <T> T evaluateExpression(String tagName,
      String attributeName, String attributeValue,
      Class<T> expectedType, Tag tagRef,
      PageContext pageContext)

You can learn more at this Java Generics FAQ.

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