Servlet

Sample

HelloServlet.java:

../../misc/howto/java/HelloServlet.java.txt

Jetty, Simple HTTP Server, Simple HTTP Server
Sample project in Subversion: sample-servlet. See the site documentation for more information.

Configuration

Create your own servlet class (probably by extending the javax.servlet.http.HttpServlet superclass).

In your web.xml file add an init-param section with your parameter name and value:

<servlet>
    <servlet-name>ConfigurationFileServlet</servlet-name>
    <display-name>ConfigurationFileServlet</display-name>
    <description></description>
    <servlet-class>
        com.mybank.xfire.example.ConfigurationFileServlet
    </servlet-class>
    <init-param>
        <param-name>company-name</param-name>
        <param-value>Dartmoor Inn</param-value>
        <description></description>
    </init-param>
</servlet>

Override the init(ServletConfig) method:

public void init(ServletConfig config) throws ServletException {
    super.init(config);
    String parameter = config.getInitParameter("company-name");
    logger.debug("init(ServletConfig) company-name [" + parameter + "]");
}

Exception

How to send an error or throw an exception from a servlet:

It appears that the error MUST be sent (or the exception thrown) before out.close();

e.g.

response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);

or…

throw new NullPointerException("Simulate an http 500 response...");
// sometime after...
out.close();

Example project in Subversion: http://myserver/svn/home/patrick/test/simulate-coldfusion/

src/main/java/com/mycompany/example/MyServlet.java

Files/Property Files

Example project in Subversion: http://g1/svn/home/patrick/learn/xfire-template.

Create your file below the WEB-INF folder. I created my properties file in a config folder:

src/main/webapp/WEB-INF/config/my.properties

Create your own servlet class (probably by extending the javax.servlet.http.HttpServlet superclass).

Override one of the init() methods:

private static final String PROPERTY_FILE_NAME = "/WEB-INF/config/my.properties";

public void init() throws ServletException {
    super.init();
    logger.debug("init()");
    InputStream stream = openPropertyFile(PROPERTY_FILE_NAME);
    Properties props = loadProperties(stream);
    logger.debug("init() phone [" + props.getProperty("phone") + "]");
}

private InputStream openPropertyFile(final String fileName) throws ServletException {
    InputStream stream = getServletContext().getResourceAsStream(fileName);
    if (stream == null) {
        throw new ServletException("Cannot load [" + fileName + "]");
    }
    return stream;
}

private Properties loadProperties(InputStream stream) throws ServletException {
    Properties props = new Properties();
    try {
        props.load(stream);
    } catch (IOException e) {
        throw new ServletException("Cannot load properties.", e);
    }
    return props;
}

Maven

<dependency>
  <groupId>javax.servlet</groupId>
  <artifactId>servlet-api</artifactId>
  <version>2.3</version>
  <scope>provided</scope>
</dependency>

JRun

See JRun Servlet notes, ../coldfusion/servlet

Request

To read the parameters from an http request:

private void printParameters(final HttpServletRequest request) {
    Map map = request.getParameterMap();
    for (Iterator i = map.entrySet().iterator(); i.hasNext();) {
        Map.Entry entry = (Map.Entry) i.next();
        String key = (String) entry.getKey();
        String value  = request.getParameter(key);
        System.out.println(key + ":" + value);
    }
}

web.xml

In a Maven project, the web.xml file will be in this location:

src\main\webapp\WEB-INF\web.xml

…and will look similar to this:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <servlet>
    <servlet-name>TestServlet</servlet-name>
    <servlet-class>com.sample.learn.Test</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>TestServlet</servlet-name>
    <url-pattern>/test</url-pattern>
  </servlet-mapping>
</web-app>