Programming Tutorials

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Packaging Servlets

By: aathishankaran in JSP Tutorials on 2007年02月14日 [フレーム]

In a production environment, multiple programmers may be developing servlets for the same server. So, placing all the servlets in the top-level servlet directory results in a massive hard-to-manage directory and risks name conflicts when two developers accidentally choose the same servlet name. Packages are the natural solution to this problem. Using packages results in changes in the way the servlets are created, the way that they are compiled, and the way they are invoked.

HelloWWW.java

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloWWW extends HttpServlet {
 public void doGet(HttpServletRequest request,
 HttpServletResponse response)
 throws ServletException, IOException {
 response.setContentType("text/html");
 PrintWriter out = response.getWriter();
 String docType =
 "\n";
 out.println(docType +
 "<HTML>\n" +
 "<HEAD><TITLE>Hello WWW</TITLE></HEAD>\n" +
 "<BODY>\n" +
 "<H1>Hello WWW</H1>\n" +
 "</BODY></HTML>");
 }
}

Let us take these areas one at a time in the following three subsections. The first two changes are exactly the same as with any other Java class that uses packages; there is nothing specific to servlets.

Creating Servlets in Packages

Two steps are needed to place servlets in packages:

  1. Move the files to a subdirectory that matches the intended package name.

    For example, I will use the javasamples package for most of the rest of the servlets in this book. So, the class files need to go in a subdirectory called javasamples.

  2. Insert a package statement in the class file.

    For example, to place a class file in a package called somePackage, the first line of the file should read package somePackage;

    For example, this program presents a variation of the HelloWWW servlet that is in the javasamples package. The class file goes in
    install_dir/webpages/WEB-INF/classes/javasamples for Tomcat3.0, in install_dir/webpages/WEB-INF/servlets/javasamples for the JSWDK 1.0.1, and in install_dir/servlets/javasamples for the Java Web Server 2.0.

Compiling Servlets in Packages

There are two main ways to compile classes that are in packages. The first option is to place your package subdirectory right in the directory where the Web server expects servlets to go. Then, you would set the CLASSPATH variable to point to the directory above the one actually containing your servlets, that is, to the main servlet directory used by the Web server. You can then compile normally from within the package-specific subdirectory. For example, if your base servlet directory is C:\JavaWebServer2.0\servlets and your package name (and thus subdirectory name) is javasamples, and you are running Windows, you would do:

DOS> set CLASSPATH=C:\JavaWebServer2.0\servlets;%CLASSPATH%
DOS> cd C:\JavaWebServer2.0\servlets\javasamples
DOS> javac HelloWorld.java

The first part, setting the CLASSPATH, you probably want to do permanently, rather than each time you start a new DOS window. On Windows 95/98 you typically put the

set CLASSPATH=... statement in your autoexec.bat file

Somewhere after the line that sets the CLASSPATH to point to servlet.jar and the JSP JAR file

HelloWWW2.java

package javasamples;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloWWW2 extends HttpServlet {
 public void doGet(HttpServletRequest request,
 HttpServletResponse response)
 throws ServletException, IOException {
 response.setContentType("text/html");
 PrintWriter out = response.getWriter();
 String docType =
 "\n";
 out.println(docType +
 "<HTML>\n" +
 "<HEAD><TITLE>Hello WWW</TITLE></HEAD>\n" +
 "<BODY>\n" +
 "<H1>Hello WWW</H1>\n" +
 "</BODY></HTML>");
 }
}

On Windows, you go to the Start menu, select Settings, select Control Panel, select System, select Environment, then enter the variable and value. On Unix (C shell), you set the CLASSPATH variable by

setenv CLASSPATH /install_dir/servlets:$CLASSPATH

Put this in your .cshrc file to make it permanent. If your package were of the form name1.name2.name3 rather than simply name1 as here, the CLASSPATH should still point to the top-level servlet directory, that is, the directory containing name1. A second way to compile classes that are in packages is to keep the source code in a location distinct from the class files. First, you put your package directories in any location you find convenient. The CLASSPATH refers to this location.

Second, you use the -d option of javac to install the class files in the directory the Web server expects. An example follows. Again, you will probably want to set the CLASSPATH permanently rather than set it each time.

DOS> cd C:\MyServlets\javasamples
DOS> set CLASSPATH=C:\MyServlets;%CLASSPATH%
DOS> javac -d C:\tomcat\webpages\WEB-INF\classes HelloWWW2.java

Keeping the source code separate from the class files is the approach I use for my own development. To complicate my life further, I have a number of different CLASSPATH settings that I use for different projects, and typically use JDK 1.2, not JDK 1.1 as the Java Web Server expects. So, on Windows I find it convenient to automate the servlet compilation process with a batch file servletc.bat, as shown in (line breaks in the set CLASSPATH line inserted only for readability). I put this batch file in C:\Windows\Command or somewhere else in the Windows PATH. After this, to compile the HelloWWW2 servlet and install it with the Java Web Server, I merely go to C:\MyServlets\javasamples and do “servletc

Invoking Servlets in Packages

To invoke a servlet that is in a package, use the URL

http://host/servlet/packageName.ServletName instead of http://host/servlet/ServletName

Thus, if the Web server is running on the local system,

http://localhost/servlet/javasamples.HelloWWW2

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