table of contents

Configuring & Using Apache Tomcat

A Tutorial on Installing and Using
Jakarta Tomcat 5.5 for Servlet and JSP Development


This covers a very old Tomcat version! Unless you specifically want to useout-of-date Tomcat and Java versions, please see the up-to-date Tomcat 6 and Tomcat 7 tutorials.

Following is a guide to installing and configuring Apache Tomcat 5.5 for use as a standalone Web server (for development) that supports servlets 2.4 and JSP 2.0. (Note: Apache Tomcat is sometimes referred to as "Jakarta Tomcat" since the Apache Java effort is known as "The Jakarta Project"). This Tomcat tutorial covers version 5.5.17, but the steps are almost the same for any Tomcat 5.5.x version. For coverage of Tomcat 6 and 7, see the separate Tomcat 6 and Tomcat 7 tutorial. For coverage of older Tomcat versions (Apache Tomcat 5.0.x and Apache Tomcat 4.0.x), please see the Apache Tomcat 5.0 and 4.0 tutorial.

Using Tomcat as a deployment server or integrating Tomcat as a plugin within the regular Apache server or a commercial Web server is more complicated than what is described in this tutorial. Although such integration is valuable for a deployment scenario (see http://jakarta.apache.org/tomcat/tomcat-5.5-doc/), my goal here is to show how to use Tomcat as a development server on your desktop. Regardless of what deployment server you use, you'll want a standalone server on your desktop to use for development.

The examples here assume you are using Windows, but they can be easily adapted for MacOS, Linux, Solaris, and other versions of Unix. Except when I refer to specific Windows paths (e.g., C:\blah\blah), I use URL-style forward slashes for path separators (e.g., install_dir/webapps/ROOT). Adapt as necessary.

The information here is adapted from the introductory setup and configuration chapter of Core Servlets and JavaServer Pages, 2nd Edition, Volume 1 from Sun Microsystems Press and Prentice Hall. For the book table of contents, index, source code, etc., please see http://volume1.coreservlets.com/. For information on training courses (either at public venues or on-site at your company) taught by the author of the book and this Apache Tomcat tutorial, please see the servlet, JSP, Struts, JSF, AJAX, and Java 5 training courses page. To report errors or omissions in this writeup or to inquire about on-site training courses on servlets, JSP, Struts, JSF, AJAX, Java 5, and other J2EE technologies, please contact Marty Hall at hall@coreservlets.com.


Executive Summary

Most people will just want to download the preconfigured Tomcat version, set JAVA_HOME and CLASSPATH, and they are done. But following is a summary of the steps for people who want to change the configuration or do it themselves. This section gives a summary of the required steps; I give extremely detailed instructions in the following sections.


Install the JDK

Your first step is to download and install Java. The servlet 2.4 (JSP 2.0) specification requires JDK 1.3 or later; J2EE 1.4 (which includes servlets 2.4 and JSP 2.0) requires JDK 1.4 or later. You might as well get a recent Java version, so use JDK 1.4 or 1.5. If you know which of those Java versions will be used on your project, get that one. In general, I recommend JDK 1.5. See the following sites for download and installation information.

Once you've installed Java, confirm that everything including your PATH is configured properly by opening a DOS window and typing "java -version" and "javac -help". You should see a real result both times, not an error message about an unknown command. Or, if you use an IDE, compile and run a simple program to confirm that the IDE knows where you installed Java.

For example, if you have JDK 1.5_08, you could set your PATH by putting the following line in your C:\autoexec.bat file.

    set PATH="C:\Program Files\Java\jdk1.5.0_08\bin";%PATH%
		

On Windows XP, you could also go to the Start menu, select Control Panel, choose System, click on the Advanced tab, press the Environment Variables button at the bottom, and enter the PATH variable and value directly. On Windows 2000 and NT, you do Start, Settings, Control Panel, System, then Environment. However, you can use C:\autoexec.bat on those versions of Windows also (unless a system administrator has set your PC to ignore it).


Configure Tomcat

Configuring Tomcat involves five main steps and four optional steps:

  1. Downloading the Jakarta Tomcat software.
  2. Setting the JAVA_HOME variable.
  3. Changing the port from 8080 to 80.
  4. Telling Tomcat to reload servlets when they are modified.
  5. Enabling the invoker servlet
  6. Changing the DOS memory settings. (Win98/Me only)
  7. Setting the CATALINA_HOME variable. (Optional; rarely used)
  8. Using a preconfigured version of Tomcat with these changes already made. (Optional; widely used)
  9. Using the Windows .exe installer instead of the .zip file. (Not Recommended)

Details of each step are given below. If Tomcat is already running, restart it after performing these steps.

1. Download the Apache Tomcat Software

Go to http://tomcat.apache.org/download-55.cgi and download and unpack the zip file for the current release build of Tomcat 5.5.

Using Tomcat with JDK 1.5 (Java 5) is preferred, but if you use Tomcat with JDK 1.4, you have to also download and unpack the "Compat" zip file. The the preconfigured Tomcat version already contains the "Compat" files and can be used with either Java 5 (1.5) or Java 1.4.

Save the zip file(s) on your PC and unzip into a location of your choice. You specify the top-level directory (e.g., C:\) and the zip file has embedded subdirectories (e.g., apache-tomcat-5.5.17). Thus, C:\apache-tomcat-5.5.17 is a common resultant installation directory. Note: from this point forward, I'll refer to that location as install_dir. For Windows, there is also a .exe installer; I prefer the .zip file, but see the .exe installer section for notes on the differences between the two.

Alternatively, you can use my preconfigured Jakarta Tomcat version. This version already has the port changed to 80, servlet reloading enabled, the invoker servlet turned on, and the "Compat" package included. It also comes with a sample development directory, autoexec.bat file, startup/shutdown shortcuts, and shortcuts for deploying applications.

2. Set the JAVA_HOME Variable

Next, you must set the JAVA_HOME environment variable to tell Tomcat where to find Java. Failing to properly set this variable prevents Tomcat from compiling JSP pages. This variable should list the base JDK installation directory, not the bin subdirectory. For example, on almost any version of Windows, if you use JDK 1.5_08, you might put the following line in your C:\autoexec.bat file.

    set JAVA_HOME=C:\Program Files\Java\jdk1.5.0_08
	

On Windows XP, you could also go to the Start menu, select Control Panel, choose System, click on the Advanced tab, press the Environment Variables button at the bottom, and enter the JAVA_HOME variable and value directly. On Windows 2000 and NT, you do Start, Settings, Control Panel, System, then Environment. However, you can use C:\autoexec.bat on those versions of Windows also (unless a system administrator has set your PC to ignore it).

3. Change the Port to 80

Assuming you have no other server already running on port 80, you'll find it convenient to configure Tomcat to run on the default HTTP port (80) instead of the out-of-the-box port of 8080. Making this change lets you use URLs of the form http://localhost/blah instead of http://localhost:8080/blah. Note that you need admin privileges to make this change on Unix/Linux. Also note that some versions of Windows XP automatically start IIS on port 80. So, if you use XP and want to use port 80 for Tomcat, you may need to disable IIS (see the Administrative Tools section of the Control Panel).

To change the port, edit install_dir/conf/server.xml and change the port attribute of the Connector element from 8080 to 80, yielding a result similar to that below.

    <Connector port="80" ...
               maxThreads="150"  ...
		

You can also:

4. Turn on Servlet Reloading

The next step is to tell Tomcat to check the modification dates of the class files of requested servlets, and reload ones that have changed since they were loaded into the server's memory. This slightly degrades performance in deployment situations, so is turned off by default. However, if you fail to turn it on for your development server, you'll have to restart the server every time you recompile a servlet that has already been loaded into the server's memory. Since this tutorial discusses the use of Tomcat for development, this change is strongly recommended.

To turn on servlet reloading, edit Edit install_dir/conf/context.xml and change

    <Context>
	
to
    <Context reloadable="true">
	

You can also:

5. Enable the Invoker Servlet

The invoker servlet lets you run servlets without first making changes to your Web application's deployment descriptor (i.e., the WEB-INF/web.xml file). Instead, you just drop your servlet into WEB-INF/classes and use the URL http://host/servlet/ServletName (or http://host/webAppName/servlet/ServletName once you start using your own Web applications; see Section 2.11 of the book for details on Web apps). The invoker servlet is extremely convenient when you are learning and even when you are doing your initial development. You almost certainly want to enable it when learning, but you should disable it again before deploying any real applications.

To enable the invoker servlet, uncomment the following servlet and servlet-mapping elements in install_dir/conf/web.xml. Do not confuse this Apache Tomcat-specific web.xml file with the standard one that goes in the WEB-INF directory of each Web application.

    <servlet>
        <servlet-name>invoker</servlet-name>
        <servlet-class>
          org.apache.catalina.servlets.InvokerServlet
        </servlet-class>
        ...
    </servlet>
    ...
    <servlet-mapping>
        <servlet-name>invoker</servlet-name>
        <url-pattern>/servlet/*</url-pattern>
    </servlet-mapping>
	

You can also:

6. Change DOS Memory Settings (Win 98/Me Only)

If you use Windows 98/Me, you may also have to change the DOS memory settings for the startup and shutdown scripts. If you get an "Out of Environment Space" error message when you start the server, you will need to right-click on install_dir/bin/startup.bat, select Properties, select Memory, and change the Initial Environment entry from Auto to at least 2816. Repeat the process for install_dir/bin/shutdown.bat. This step is not necessary in recent versions of Windows.

7. Set the CATALINA_HOME Variable (Optional)

If you are going to make copies of the Tomcat startup or shutdown scripts (e.g., startup.bat and shutdown.bat), it is also helpful to set the CATALINA_HOME environment variable to refer to the top-level directory of the Apache Tomcat installation (e.g., C:\apache-tomcat-5.5.17). This variable identifies the Tomcat installation directory to the server. However, if you are careful to avoid copying the server scripts and you use only shortcuts (called "symbolic links" on Unix/Linux) instead, you are not required to set this variable. I recommend using shortcuts and not bothering with CATALINA_HOME.

8. Using the Preconfigured Tomcat Version (Optional)

Please see the preconfigured Tomcat page on installing Jakarta Tomcat 5.5 with all settings already made. Just unzip the file, set your JAVA_HOME and CLASSPATH variables, and you are read to go.

9. Using the Windows .exe Installer

If you are using Microsoft Windows, you can download a .exe installer instead of the .zip file discussed in this tutorial. In my opinion, it is not worth the bother to do so, but some people like it. If you use it, note these differences:

  • It will prompt you for the desired port. It will ask you what port it should run on, and make the changes in server.xml for you. You will still need to manually edit context.xml and web.xml, however.
  • It will set JAVA_HOME for you. The installer hunts for your Java installation and tries to set JAVA_HOME appropriately. This is a convenience, albeit a minor one.
  • It will setup Start Menu entries. In particular, instead of using startup.bat and shutdown.bat, you can go to the Start Menu, select Apache Tomcat 5.5, select Monitor Tomcat, and select Start or Stop, as shown below. I prefer startup.bat and shutdown.bat so that I can put shortcuts in my development directory (easier to invoke) and/or the desktop (where I can associate keyboard shortcuts).

    Tomcat 5 Monitor


Test the Server

Testing the server involves three steps:

  1. Verifying that the server can even start.
  2. Checking that you can access your own HTML and JSP pages.
  3. Seeing if you can compile and run simple servlets.

1. Verify That the Server Can Start

Before trying your own servlets or JSP pages, you should make sure that the server is installed and configured properly. For Tomcat, click on install_dir/bin/startup.bat (or execute install_dir/bin/startup.sh on Unix/Linux). Next, enter the URL http://localhost/ in your browser and make sure you get the Tomcat welcome page, not an error message saying that the page could not be displayed or that the server could not be found. If you chose not to change the port number to 80 as described above, you will need to use a URL like http://localhost:8080/ that includes the port number.

If this does not work, there are a couple of things to check:

  • Did the Tomcat window pop up and stay open? If not, the error messages are lost and it is hard to know what you did wrong. So, open a DOS window, go to install_dir/bin and type "catalina run" to start Tomcat without popping up a new window. Now, the error messages should help you figure out the problem (e.g., JAVA_HOME not set properly or IIS already reserving port 80).
  • Does the server appear to be running but you cannot access the home page? Maybe your browser is using a proxy and you have not set it to bypass proxies for local addresses? To fix this:
    • On Internet Explorer, go to Tools, Internet Options, Connections, and LAN Settings. If the "Use a proxy server" checkbox is selected, make sure the "Bypass proxy server for local addresses" box is also selected.
    • On Netscape 6/7, go to the Edit menu, then select Preferences, Advanced, and Proxies. Then enter "localhost" in the textfield labeled "No Proxy for:".
    • On Mozilla Firefox go to Tools, Internet Options, and Connections. Make sure "localhost" is in the textfield labeled "No Proxy for:". Note that this entry is the default with Firefox, so you probably do not need to change it.

To halt the server, double click on install_dir/bin/shutdown.bat. I recommend that you make shortcuts to (not copies of) the startup and shutdown scripts and place those shortcuts on the desktop or in your main development directory. If you put them on the desktop, you can assign keyboard shortcuts, which is convenient.

2. Try Some Simple HTML and JSP Pages

After you have verified that the server is running, you should make sure that you can install and access simple HTML and JSP pages. This test, if successful, shows two important things. First, successfully accessing an HTML page shows that you understand which directories should hold HTML and JSP files, and what URLs correspond to them. Second, successfully accessing a new JSP page shows that the Java compiler (not just the Java virtual machine) is configured properly.

Eventually, you will almost certainly want to create and use your own Web applications, but for initial testing many people prefer to use the default Web application. With Tomcat and the default Web application, you put HTML and JSP pages in install_dir/webapps/ROOT or install_dir/webapps/ROOT/somePath and access them with http://localhost/filename or http://localhost/somePath/filename.

For your first tests, I suggest you simply take Hello.html and Hello.jsp and drop them into the appropriate locations. Right click on the links to download these two files to your system. If you download the files using Internet Explorer, just be careful that it does not try to change the file extension, yielding Hello.htm instead of Hello.html. The code for these files, as well as all the code from the book, is available online at http://volume1.coreservlets.com. That Web site also contains book updates, additions, information on servlet and JSP short courses, and the full text of the first edition of Core Servlets and JavaServer Pages and More Servlets and JSP (in PDF). Note also that the preconfigured Tomcat version already contains all the test files, and has shortcuts from the development directory to the deployment locations.

If you put the files in the top-level directory of the default Web application (i.e., in install_dir/webapps/ROOT), access them with the URLs http://localhost/Hello.html and http://localhost/Hello.jsp, respectively. If you put them in a subdirectory of install_dir/webapps/ROOT, use the URLs http://localhost/directoryName/Hello.html and http://localhost/directoryName/Hello.jsp, respectively.

If you successfully started the server as described above, but neither the HTML file nor the JSP file works (e.g., you get File Not Found--404--errors), you likely are using the wrong directory for the files. If the HTML file works but the JSP file fails, you probably have incorrectly specified the base JDK directory (i.e., with the JAVA_HOME variable).

3. Try Compiling and Deploying Servlets

After you set up your development environment, be sure to come back and verify that you can compile and run servlets.


Set Up Your Development Environment

The server startup script startup.bat automatically sets the server's CLASSPATH to include the standard servlet and JSP classes and the WEB-INF/classes directory (containing compiled servlets) of each Web application. But you need similar settings, or you will be unable to compile servlets in the first place. Configuring your system for servlet development involves the following four steps:

  1. Creating a development directory
  2. Making shortcuts to the Tomcat startup and shutdown scripts
  3. Setting your CLASSPATH
  4. Bookmarking the servlet & JSP javadocs

Details on each step are given below.

1. Create a Development Directory

The first thing you should do is create a directory in which to place the servlets and JSP pages that you develop. This directory can be in your home directory (e.g., C:\Documents and Settings\Your Name\My Documents\Servlets+JSP on Windows 2000) or in a convenient general location (e.g., C:\Servlets+JSP). It should not, however, be in the Tomcat deployment directory (e.g., anywhere within install_dir/webapps).

Eventually, you will organize this development directory into different Web applications. For initial testing of your environment, however, you can just put servlets either directly in the development directory (for packageless servlets) or in a subdirectory that matches the servlet package name. Many developers simply put all their code in the server's deployment directory (within install_dir/webapps). I strongly discourage this practice and instead recommend one of the approaches described in the deployment section. Although developing in the deployment directory seems simpler at the beginning since it requires no copying of files, it significantly complicates matters in the long run. Mixing locations makes it hard to separate an operational version from a version you are testing, makes it difficult to test on multiple servers, and makes organization much more complicated. Besides, your desktop is almost certainly not the final deployment server, so you'll eventually have to develop a good system for deploying anyhow.

Note that the preconfigured Tomcat version already contains all the test files, has shortcuts from the development directory to the deployment locations, and has shortcuts to start and stop the server.

2. Make Shortcuts to Start and Stop the Server

Since I find myself frequently restarting the server, I find it convenient to place shortcuts to the server startup and shutdown scripts inside my main development directory or on my desktop. You will likely find it convenient to do the same.

For example, one way to make these shortcuts is to go to install_dir/bin, right-click on startup.bat, and select Copy. Then go to your development directory, right-click in the window, and select Paste Shortcut (not just Paste). Repeat the process for install_dir/bin/shutdown.bat. If you put the shortcuts on your desktop, you can also assign keyboard shortcuts to invoke them. On Unix, you would use ln -s to make a symbolic link to startup.sh, catalina.sh (needed even though you don't directly invoke this file), and shutdown.sh.

3. Set Your CLASSPATH

Since servlets and JSP are not part of the Java 2 platform, standard edition, you have to identify the servlet classes to the compiler. The server already knows about the servlet classes, but the compiler (i.e., javac) you use for development probably doesn't. So, if you don't set your CLASSPATH, attempts to compile servlets, tag libraries, filters, Web app listeners, or other classes that use the servlet and JSP APIs will fail with error messages about unknown classes. Here are the standard Tomcat locations:

  • install_dir/common/lib/servlet-api.jar
  • install_dir/common/lib/jsp-api.jar

You need to include both files in your CLASSPATH.

Now, in addition to the servlet JAR file, you also need to put your development directory in the CLASSPATH. Although this is not necessary for simple packageless servlets, once you gain experience you will almost certainly use packages. Compiling a file that is in a package and that uses another class in a user-defined package requires the CLASSPATH to include the directory that is at the top of the package hierarchy. In this case, that's the development directory I just discussed. Forgetting this setting is perhaps the most common mistake made by beginning servlet programmers!

Finally, you should include "." (the current directory) in the CLASSPATH. Otherwise, you will only be able to compile packageless classes that are in the top-level development directory.

Here are two representative methods of setting the CLASSPATH. They assume that your development directory is C:\Servlets+JSP. Replace install_dir with the actual Tomcat installation path (e.g., C:\apache-tomcat-5.5.17). Also, be sure to use the appropriate case for the filenames, and enclose your pathnames in double quotes if they contain spaces.

Any Windows Version from Windows 98/Me Onward. Use the autoexec.bat file.

  • Sample code: (Note that this all goes on one line with no spaces--it is broken here only for readability.)
    set CLASSPATH=.;
        C:\Servlets+JSP;
        install_dir\common\lib\servlet-api.jar;
        install_dir\common\lib\jsp-api.jar
  • Sample file to download and modify: autoexec.bat

Note that these examples represent only one approach for setting the CLASSPATH. Many Java integrated development environments have global or project-specific settings that accomplish the same result. But these settings are totally IDE-specific and won't be discussed here. Another alternative is to make a .bat file or ant build script whereby -classpath ... is automatically appended onto calls to javac.

Windows NT/2000/XP. You could use the autoexec.bat file as above, but a more common approach is to use system settings. On WinXP, go to the Start menu and select Control Panel, then System, then the Advanced tab, then the Environment Variables button. On Win2K/WinNT, go to the Start menu and select Settings, then Control Panel, then System, then Environment. Either way, enter the CLASSPATH value from the previous bullet.

4. Bookmark the Servlet and JSP API Documentation

Just as no serious programmer should develop general-purpose Java applications without access to the JDK API documentation (in Javadoc format), no serious programmer should develop servlets or JSP pages without access to the API for classes in the javax.servlet packages.

You can access the documentation from the Tomcat home page, but you probably will want access to the API even when the server is not running. So, I recommend you open the top-level API files directly from disk and bookmark those locations.

Here are the standard locations:

  • Servlet API: install_dir/webapps/tomcat-docs/servletapi/index.html
  • JSP API: install_dir/webapps/tomcat-docs/jspapi/index.html

Compile and Test Some Simple Servlets

OK, so your environment is all set. At least you think it is. It would be nice to confirm that hypothesis. Verifying this involves the following three steps:

  1. Testing a packageless servlet
  2. Testing a servlet that uses packages
  3. Testing a servlet that uses packages and utility classes

Details on each step are given below.

Test 1: A Servlet That Does Not Use Packages

The first servlet to try is a basic one: no packages or utility (helper) classes. Rather than writing your own test servlet, you can just download HelloServlet.java into your development directory, compile it, and copy the .class file to install_dir/webapps/ROOT/WEB-INF/classes. Right-click on the link to download the file to your system. Note: in all versions of Apache Tomcat, the location for servlets in the default Web application is install_dir/webapps/ROOT/WEB-INF/classes. However, in recent versions of Tomcat (including Tomcat 5.5.17), the system doesn't create the directory for you automatically. No problem: just create it yourself. (Remember that case matters: WEB-INF is upper case, classes is lower case.) Note that my preconfigured Apache Tomcat version already contains the classes directory and already has the sample servlets.

What about install_dir/shared/classes?

"Hey, wait! Shouldn't I use install_dir/shared/classes instead of install_dir/webapps/ROOT/WEB-INF/classes?"

Nope. There are two reasons why it is preferable to use install_dir/webapps/ROOT/WEB-INF/classes:

1. It is standard. The ROOT directory follows the normal structure of a Web application (see Section 2.11 of the book): HTML/JSP files go in the main directory, the web.xml file goes in WEB-INF, unjarred Java classes go in WEB-INF/classes, and JAR files go in WEB-INF/lib. So, if you use WEB-INF/classes, you are using a structure that works on all servers that support servlets 2.2 and later. On the other hand, install_dir/shared/classes is a Tomcat-specific location that is supported on few, if any, other servers.

2. It is specific to a Web application. Once you become comfortable with the basics, you will almost certainly divide your projects up into separate Web applications. By putting your code in WEB-INF/classes, you are ready for this, since your code is already part of a Web application (the default one for Tomcat). So, the code can easily move to another Web application, and it will not interfere with any future applications. On the other hand, install_dir/shared/classes results in code that is shared by all Web applications on your server. This is almost never what you want for servlets.

If you get compilation errors, go back and check your CLASSPATH settings (see the earlier section on this topic)--you most likely erred in listing the location of the JAR files that contains the servlet and JSP classes. Once you compile HelloServlet.java, put HelloServlet.class in install_dir/webapps/ROOT/WEB-INF/classes. After compiling the code, access the servlet with the URL http://localhost/servlet/HelloServlet (or http://localhost:8080/servlet/HelloServlet if you chose not to change the port number as described earlier). You should get a simple HTML page that says "Hello". If this URL fails but the test of the server itself succeeded, you probably put the class file in the wrong directory or forgot to enable the invoker servlet.

Test 2: A Servlet That Uses Packages

The second servlet to try is one that uses packages but not utility classes. Again, rather than writing your own test, you can download and install HelloServlet2.java. Since this servlet is in the coreservlets package, it should go in the coreservlets directory both during development and when deployed to the server. Once you compile HelloServlet2.java, put HelloServlet2.class in install_dir/webapps/ROOT/WEB-INF/classes/coreservlets. For now, you can simply copy (not move!) the coreservlets subdirectory from the development directory to install_dir/webapps/ROOT/WEB-INF/classes. An upcoming section will provide some other options for the deployment process.

Once you have placed the servlet in the proper directory, access it with the URL http://localhost/servlet/coreservlets.HelloServlet2. You should get a simple HTML page that says "Hello (2)". If the first test succeeded but this test failed, you probably either typed the URL wrong (e.g., used a slash instead of a dot after the package name) or put HelloServlet2.class in the wrong location (e.g., directly in install_dir/webapps/ROOT/WEB-INF/classes directory instead of in the coreservlets subdirectory).

Test 3: A Servlet That Uses Packages and Utilities

The final servlet you should test to verify the configuration of your server and development environment is one that uses both packages and utility classes. HelloServlet3.java is a servlet in the coreservlets package that uses the ServletUtilities class to simplify the generation of the DOCTYPE (specifies the HTML version--useful when using HTML validators) and HEAD (specifies the title) portions of the HTML page. Those two parts of the page are useful (technically required, in fact), but are tedious to generate with servlet println statements. Since both the servlet and the utility class are in the coreservlets package, they should go in the coreservlets directory.

If you get compilation errors such as "Unresolved symbol: ServletUtilities", check the following two things.

  • That you put the classes in the coreservlets subdirectory, not directly in your development directory. Packaged Java code should always be placed in a subdirectory matching the package name.
  • That your CLASSPATH is set properly. If this is the cause of your problem, you most likely forgot to include the top-level development directory (i.e., the directory above the package-specific subdirectory). I've said it before, but I'll say it again: your CLASSPATH must include the top-level directory of your package hierarchy before you can compile a packaged class that makes use of another class from a user-defined package. This requirement is not particular to servlets; it is the way packages work on the Java platform in general. Nevertheless, many servlet developers are unaware of this fact, and it is one of the (perhaps the) most common errors beginning developers encounter.

Please don't send me email about unresolved symbol errors until you have confirmed that HelloServlet3.java and ServletUtilities.java are in a subdirectory called coreservlets, and that the directory above this is in the CLASSPATH.

Once you compile HelloServlet3.java (which will automatically cause ServletUtilities.java to be compiled), copy (don't move!) the entire coreservlets subdirectory from your development location to install_dir/webapps/ROOT/WEB-INF/classes. Then, access the servlet with the URL http://localhost/servlet/coreservlets.HelloServlet3 (again, note that it is a dot, not a slash, between the package name and the servlet name). You should get a simple HTML page that says "Hello (3)".

Establish a Simplified Deployment Method

OK, so you have a development directory. You can compile servlets with or without packages. You know which directory the servlet classes belong in. You know the URL that should be used to access them. (Actually, http://hostname/servlet/ServletName is just the default URL; you can also use the web.xml file to customize that URL; for details, see Section 2.11 of the book.) But how do you move the class files from the development directory to the deployment directory? Copying each one by hand every time is tedious and error prone. Once you start using Web applications, copying individual files becomes even more cumbersome.

There are several options to simplify the process. Here are a few of the most popular ones. If you are just beginning with servlets and JSP, you probably want to start with the first option and use it until you become comfortable with the development process. Note that I do not list the option of putting your code directly in the server's deployment directory. Although this is one of the most common choices among beginners, it scales so poorly to advanced tasks that I recommend you steer clear of it from the start.

  1. Copy to a shortcut or symbolic link.
  2. Use the -d option of javac.
  3. Let your IDE take care of deployment.
  4. Use ant or a similar tool.

Details on these four options are given below.

1. Copy to a Shortcut or Symbolic Link

Go to install_dir/webapps/ROOT/WEB-INF, right-click on the classes directory, and select Copy. Then go to your development directory, right-click, and select Paste Shortcut (not just Paste). Note that if you use my preconfigured Jakarta Tomcat version, this shortcut is already in your C:\Servlets+JSP directory. Now, whenever you compile a packageless servlet, just drag the class files onto the shortcut. When you develop in packages, use the right mouse to drag the entire package directory (e.g., the coreservlets directory) onto the shortcut, release the mouse, and select Copy. On Unix/Linux, you can use symbolic links (created with ln -s) in a manner similar to that for Windows shortcuts.

An advantage of this approach is that it is simple. So, it is good for beginners who want to concentrate on learning servlets and JSP, not deployment tools. Another advantage is that a variation applies once you start using your own Web applications. (See Chapters 4-6 of More Servlets and JSP for details on Web applications). For instance, with Tomcat, you can easily make your own Web application by putting a copy of the install_dir/webapps/ROOT directory into your development directory and renaming it (for example, to testApp). Now, to deploy your Web application, just make a shortcut to install_dir/webapps and copy the entire Web application directory (e.g., testApp) each time by using the right mouse to drag the directory that contains your Web application onto this shortcut and selecting Copy (say Yes when asked if you want to replace existing files). The URL stays almost the same as it was without Web applications: just insert the name of the directory after the hostname (e.g., replace http://localhost/blah/blah with http:/localhost/testApp/blah/blah).

Note that the preconfigured Tomcat version already contains all the test files, has shortcuts from the development directory to the deployment locations, and has shortcuts to start and stop the server.

One disadvantage of this approach is that it requires repeated copying if you use multiple servers. For example, I usually have Apache Tomcat, Macromedia JRun, and Caucho Resin on my desktop system and regularly test my code with all three servers. A second disadvantage is that this approach copies both the Java source code files and the class files to the server, whereas only the class files are needed. This does not matter on your desktop development server, but when you get to the "real" deployment server, you won't want to include the source code files.

2. Use the -d Option of javac

By default, the Java compiler (javac) places class files in the same directory as the source code files from which they came. However, javac has an option (-d) that lets you designate a different location for the class files. You need only specify the top-level directory for class files--javac will automatically put packaged classes in subdirectories that match the package names. So, for example, I could compile the HelloServlet2 servlet as follows (line break added only for clarity; omit it in real life).

	javac -d install_dir/webapps/ROOT/WEB-INF/classes
			 HelloServlet2.java
	

You could even make a Windows batch file or Unix shell script or alias that makes a command like servletc expand to javac -d install_dir/.../classes. See http://java.sun.com/j2se/1.4/docs/tooldocs/win32/javac.html for more details on -d and other javac options.

An advantage of this approach is that it requires no manual copying of class files. Furthermore, the exact same command can be used for classes in different packages since javac automatically puts the class files in subdirectories matching the package names.

The main disadvantage of this approach is that it applies only to Java class files; it won't work for deploying HTML and JSP pages, much less entire Web applications.

3. Let Your IDE Take Care of Deployment

Most servlet- and JSP-savvy development environments (e.g., Eclipse, Borland JBuilder, Sun Java Studio Creator) have options that let you tell the IDE where to deploy class files for your project. Then, when you tell the IDE to build the project, the class files are automatically deployed to the proper location (package-specific subdirectories and all).

An advantage of this approach, at least in most IDEs, is that it can deploy HTML and JSP pages and even entire Web applications, not just Java class files. A disadvantage is that it is an IDE-specific technique and thus is not portable across systems.

4. Use ant or a Similar Tool

Developed by the Apache foundation's Jakarta project, ant is a tool similar to the Unix make utility. However, ant is written in the Java programming language (and thus is portable) and is touted to be both simpler to use and more powerful than make. Many servlet and JSP developers use ant for compiling and deploying. The use of ant is especially popular among Tomcat users and with those developing Web applications.

For general information on using ant, see http://jakarta.apache.org/ant/manual/. See Tomcat Documentation for specific guidance on using ant with Tomcat.

The main advantage of this approach is flexibility: ant is powerful enough to handle everything from compiling the Java source code files, to copying class files, to producing WAR files. The disadvantage of ant is the overhead of learning to use it; there is more of a learning curve with ant than with the other techniques in this section.


Using A Preconfigured Tomcat Version

If you prefer not to individually make each of the changes described in this tutorial, you can download a version of Jakarta Tomcat that has all of these changes already made. All you have to do is unzip the file and set your JAVA_HOME and CLASSPATH variables, and you are ready to run. In particular, this Tomcat version:

  • Has the port changed from 8080 to 80 (so you do not have to type the port number in the URL).
  • Has servlet reloading turned on (so you do not have to restart the server if you change a servlet .class file).
  • Has the invoker servlet enabled (so you can invoke servlets with http://localhost/servlet/ServletName, without making changes to web.xml or restarting the server).
  • Includes the sample HTML page, JSP page, servlets, and utility classes needed to test your setup.
  • Includes a sample development directory with shortcuts to ROOT, ROOT/WEB-INF/classes, startup.bat, and shutdown.bat.
  • Includes an autoexec.bat file that sets the PATH, CLASSPATH, and JAVA_HOME variables. Be sure you edit this file to refer to the proper JDK path, and be sure to save your original autoexec.bat file, if you have one.

Deploy Using Custom Web Applications

For learning and practicing specific servlet and JSP techniques, it is simplest to use Tomcat's default Web application (ROOT) and to use the "invoker servlet" that lets you run servlets by putting /servlet/ServletName at the end of the URL. When you start developing your real project, however, you almost always use custom Web applications (and never use the invoker servlet). This section gives a quick summary on the use of Web applications in Tomcat. For more details, see the Web application sections of the JSP and servlet training materials page.

Learning Deployment

  • Use default Web application (ROOT on Tomcat)
  • Use default URLs (http:///servlet/ServletName)
  • Advantages
    • Simpler. Just drop the servlet in the right location and test immediately. This is far easier than editing web.xml every time you create a new servlet.
    • Can test without restarting server or editing web.xml (although Tomcat 5.5 usually notices when web.xml has been modified, and reloads the Web app automatically when it has)
  • Use a custom Web application (on Tomcat, a directory in install_dir/webapps with structure similar to ROOT)
  • Register custom URLs in WEB-INF/web.xml
  • Advantages
    • URLs look better. No class names in the URLs.
    • Advanced features (init params, security, filters, etc.) depend on your using registered URLs. The invoker servlet is just a convenience for initial testing; never use it for real applications!

Using custom Web apps involves the following steps:

  1. Making a directory whose structure mirrors the structure of the default Web application.
  2. Updating your CLASSPATH
  3. Using the directory name in the URL
  4. Using web.xml to assign custom URLs

1. Make a directory whose structure mirrors the structure of the default Web application.

  • HTML, JSP, images, style sheets, and other regular Web content goes in the top-level directory (or any subdirectory other than WEB-INF or META-INF).
  • The web.xml file goes in the WEB-INF subdirectory
  • Servlets and other classes go either in WEB-INF/classes (unpackaged servlets) or a subdirectory of WEB-INF/classes that matches the package name.
  • On Tomcat, entire directory is deployed in install_dir/webapps. One of the simplest approaches is to create the Web app in your development directory (e.g., C:\Servlets+JSP), then copy the entire directory to install_dir/webapps whenever you want to test it. Simplify the process by keeping a shortcut to install_dir/webapps in C:\Servlets+JSP.

Note that you can also deploy using WAR files instead of regular directories. A WAR file is just a JAR file (which is just a ZIP file) with a .war extension. You can create WAR files using jar, WinZip, or the Windows XP "Create Compressed Folder" R-Mouse option. If you use WAR files, a directory such as myWebApp should become myWebApp.war, and the top-level directory within the WAR file should be WEB-INF (i.e., do not repeat myWebApp within the WAR file).

2. Update your CLASSPATH

If your Web application directory is myWebApp, your CLASSPATH should include mainDevelDir/myWebApp/WEB-INF/classes. A convenient trick is to include .. and ../.. in your CLASSPATH so that you never need to update your CLASSPATH as long as you stick with singly and doubly nested packages. The CLASSPATH setting in the preconfigured Tomcat version uses this trick.

3. Use the directory name in the URL

All URLs should be of the form http://hostname/myWebApp/... . For example, if Hello.html is in the top-level directory of the Web app and you are running on your desktop system, once the Web app is deployed (copied to tomcat_dir/webapps), the file would be accessed with http://localhost/myWebApp/Hello.html. In general, you use the same URLs as for the default Web app (ROOT) except that you insert /myWebApp right after the hostname.

4. Use web.xml to assign custom URLs

First, you use servlet and servlet-mapping elements to give the servlet an address relative to the Web application, as below: (note that the servlet-name is arbitrary, but you have to use the same name in both the servlet and servlet-mapping entries)

	<?xml version="1.0" encoding="ISO-8859-1"?>
	<web-app xmlns="http://java.sun.com/xml/ns/j2ee"
		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
		version="2.4">
	  <servlet>
		<servlet-name>Servlet2</servlet-name>
		<servlet-class>coreservlets.HelloServlet2</servlet-class>
	  </servlet>
	  <servlet-mapping>
		<servlet-name>Servlet2</servlet-name>
		<url-pattern>/servlet2</url-pattern>
	  </servlet-mapping>
	</web-app>
	

If you deployed HelloServlet2 in the myWebApp application using the invoker servlet, it would go in .../myWebApp/WEB-INF/classes/coreservlets and be invoked with the URL http://localhost/myWebApp/servlet/coreservlets.HelloServlet2. If you used a registered URL of servlet2 as above, the class file would still go in .../myWebApp/WEB-INF/classes/coreservlets, but it would be invoked with the URL http://localhost/myWebApp/servlet2


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