2.21.1. Create a Servlet in a package ¶

The WEB-INF/classes directory contains all Servlet classes and other class files, and the directory structure of the class files matches their package name. For example, if you have a fully qualified class name com.myorg.MyServlet , then the Servlet class must be located in the following directory

/myapp/WEB-INF/classes/com/myorg/MyServlet.class

The following example creates a package named com.myorg the MyServlet class.

// Package Naming
package com.myorg;

// Import necessary Java libraries
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

@WebServlet("/MyServlet")
public class MyServlet extends HttpServlet {

  private String message;

  public void init() throws ServletException
  {
      // Perform necessary initialization
      message = "Hello World";
  }

  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
            throws ServletException, IOException
  {
      // Set response content type
      response.setContentType("text/html;charset=UTF-8");

      // The actual logic is here
      PrintWriter out = response.getWriter();
      out.println("<h1>" + message + "</h1>");
  }

  public void destroy()
  {
      // Nothing
  }
}

2.21.2. Compile the Servlet in the package ¶

Compiling classes in a package is not much different from compiling other classes. The easiest way is to keep your java file in a fully qualified path, such as the classes mentioned above, which will be kept in the com.myorg . You also need to be in the CLASSPATH add the directory.

Assuming that your environment is set up correctly, enter the <Tomcat-installation-directory>/webapps/ROOT/WEB-INF/classes directory, and compile MyServlet.java, as follows:

$ javac MyServlet.java

If Servlet depends on other libraries, you must also reference those JAR files in CLASSPATH. I only quote here. servlet-api.jar JAR file, because I don’t use any other libraries in the Hello World program.

This command line uses the built-in javac compiler, which is included with the Sun Microsystems Java Software Development Kit (JDK, Java Software Development Kit). Microsystems’s Java Software Development Kit (JDK). In order for this command to work properly, you must include the location of the Java SDK that you use in the PATH environment variable.

If all goes well, the above compilation will be generated in the same directory MyServlet.class files. The next section explains how to deploy a compiled Servlet to production.

2.21.3. Servlet packaged deployment ¶

By default, Servlet applications are located in the path <Tomcat-installation-directory>/webapps/ROOT and the class file is placed in the <Tomcat-installation-directory>/webapps/ROOT/WEB-INF/classes .

If you have a fully qualified class name com.myorg.MyServlet then the Servlet class must be located in WEB-INF/classes/com/myorg/MyServlet.class , you need to be located in the <Tomcat-installation-directory>/webapps/ROOT/WEB-INF/ of web.xml create the following entries in the file:

<servlet>
    <servlet-name>MyServlet</servlet-name>
    <servlet-class>com.myorg.MyServlet</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/MyServlet</url-pattern>
</servlet-mapping>

The above entry is to be created in the web.xml in the file <web-app>...</web-app> inside the label. There may already be various entries available in this file, but don’t worry about it.

At this point, you are basically done, now let’s use <Tomcat-installation-directory>\bin\startup.bat (on Windows) or <Tomcat-installation-directory>/bin/startup.sh (on Linux/Solaris, etc.) start the tomcat server, and finally enter http://localhost:8080/MyServlet in the address bar of the browser. If all goes well, you will see the following results:

Hello World