Develop Reference

Getting init parameter while accessing JSP file by filename

I'm trying to access init parameter in a JSP file.
When I enter a url-pattern from servlet mapping like this: http://localhost:8080/JEE_Learning/testingJSP
it works fine, the parameter is there.
But when I enter a JSP filename: http://localhost:8080/JEE_Learning/testing.jsp
the parameter is null.
web.xml:
<servlet>
<servlet-name>testingJSP</servlet-name>
<jsp-file>/testing.jsp</jsp-file>
<init-param>
<param-name>name</param-name>
<param-value>John</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>testingJSP</servlet-name>
<url-pattern>/testingJSP</url-pattern>
</servlet-mapping>
inside JSP file:
<%= getInitParameter("name") %>
Why is that?

If you add
<%=getServletConfig().getServletName()%>
to the JSP page you will see the output
testingJSP when calling .../testingJSP and
jsp when calling .../testing.jsp (in Tomcat).
So the first request invokes the testingJSP servlet the second the JSP servlet of the container. Accordingly the servlet init parameter is only defined in the first request.

If you want to access the name parameter from
http://localhost:8080/JEE_Learning/testingJSP and
http://localhost:8080/JEE_Learning/testing.jsp
then you should add
<url-pattern>/testing.jsp</url-pattern>
to your
<servlet-mapping>

Using a servlet in Liferay

I have to get an image from an url finished in /jcaptcha.jpg
I've defined in the web.xml file the following nodes:
<servlet>
<servlet-name>jcaptcha</servlet-name>
<servlet-class>com.domain.portales.jcaptcha.servlet.ImageCaptchaServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>jcaptcha</servlet-name>
<url-pattern>/jcaptcha.jpg</url-pattern>
</servlet-mapping>
In my jsp, I try to get the image, and I get it, but the code of doGet method of my servlet doesn´t execute. However, if I get the image using the following code
<p><img id="imgrecarga" src="${pageContext.request.contextPath}/jcaptcha.jpg"/></p>
that produces the value
/WCAC_FormularioContacto-portlet/jcaptcha.jpg
I obtain the image rigth and enter to the doGet() method.
It's strange because on that path doesn't exist the .jpg file.
I have to obtain the image by the first way entering on the doGet method, anyone knows what is happening? Have I to configure something on Liferay?

Finally the problem was because I was using a bad domain. For my local tests I've to access with an url starting by localhost:8080...

Adding default servlet and forwarding to an HTML creates stackoverflowerror

I am using Jetty. My default servlet is making a simple forward to an HTML file in my WEB-INF folder that is causing a java.lang.StackOverFlowError error. The error is fixed if I rename the file I am forwarding from a .html to .jsp
DefaultServlet.java
public class DefaultServlet extends HttpServlet{
#Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException{
req.getRequestDispatcher("WEB-INF/home.html").forward(req, resp);
}
}
web.xml
<web-app>
<display-name>Archetype Created Web Application</display-name>
<servlet>
<servlet-name>Default</servlet-name>
<servlet-class>DefaultServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Default</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
</web-app>
My guess is that instead of inserting the html content in the response body, the forward is sending the browser a redirect to /WEB-INF/home.html. This again calls the DefaultServlet and gets into an infinity loop. How can I prevent this?
Thanks.

The "default servlet", which is mapped on a special URL pattern of /, is a very special servlet which is invoked when there's a request which does not match any of the servlets mapped on a more specific URL pattern such as *.jsp, /foo/*, etc.
When you forward to home.html, for which apparently no one servlet is registered, then the default servlet is invoked once again. However, the default servlet is ignorantly forwarding to the very same HTML file once again instead of actually serving the requested HTML file. It'll on the forward still find no one servlet matching the forward URL and it'll still invoke the default servlet once again. And again. Etc. When this is performed so many times that the stack cannot keep track anymore of all those in sequence invoked doGet() methods (usually around 1000), then you'll get a StackOverflowError.
That it works with a JSP file has actually a very simple reason: there's already a JspServlet registered on an URL pattern of *.jsp. So the badly designed default servlet isn't invoked.
Your default servlet should instead be obtaining the HTML file's contents via ServletContext#getResourceAsStream() and write it to the HttpServletResponse#getOutputStream().
However, it's also quite possible that you completely misunderstood the whole meaning of "default servlet" and/or the special meaning of the URL pattern / and actually merely want a servlet acting as home page. In that case, you should be mapping the servlet on a more specific URL pattern (and please rename the currently obviously quite confusing class name DefaultServlet to something else):
<servlet>
<servlet-name>home</servlet-name>
<servlet-class>com.example.HomeServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>home</servlet-name>
<url-pattern>/home</url-pattern>
</servlet-mapping>
And then register exactly that URL as welcome file:
<welcome-file-list>
<welcome-file>home</welcome-file>
</welcome-file-list>

You need kind of exclude urls ends with "html".
See for example this link explaining similar problem solution Can I exclude some concrete urls from <url-pattern> inside <filter-mapping>?

How can I make an exception to /* url-pattern in web.xml?

In our web.xml, we have CXFServlet mapped to the /* url pattern:
<servlet-mapping>
<servlet-name>CXFServlet</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
This works great and we don't want to change it at this point. But I would like to have an html page (/admin/index.html) that is not handled by the CXFServlet, and is just served up directly as html. How can I accomplish this? I don't know how to create a servlet mapping just to serve an html page.
Note we are using IBM WebSphere 8 (WAS 8) if that matters.

You can try:
<servlet-mapping>
<servlet-name>CXFServlet</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>default</servlet-name>
<url-pattern>/admin/*</url-pattern>
</servlet-mapping>
It work's in Jetty and Tomcat.

None of the given answers (so far) met my requirements, but I found a simple solution that did.
For some reason it turns out that WebSphere will handle JSPs itself, rather than delegating to the servlet that has the /* mapping -- even though there is no specific mapping in web.xml mentioning JSPs. Maybe this is part of the spec and one would have to explicitly map *.jsp to a servlet if you want it to handle those requests?
In any case it works for me -- instead of using /admin/index.html I can use /admin/index.jsp (and will probably add index.jsp to welcome-file-list so that requests for /admin will also give this page).

You can have some code in CXFServlet.java
In doget() methods:
URL url = new URL(request.getRequestURL());
System.out.println("URL is:" + url);
if (url.toString().contains("/admin/")) {
response.setContentType("text/html; charset=UTF-8");
PrintWriter pw = response.getWriter();
pw.print("<!DOCTYPE html><html lang=\"fa\" dir=\"rtl\">\n"
+ "<head>"
+ "<meta charset=\"utf-8\"/>"
+ "</head>"
+ "<body>"
+ "<div>some thing</div>"
+ "<body></html>");
pw.close();
return;
}

Relay servlet (servlet calls another servlet)

Hello i have a question about servlet calling another servlet
I have a main servlet called Relay which is going to be responsible to control the other servlets
the user will click on and will be forwarded to Relay servlet
<li>Check the available animals </li>
inside Relay servlet will get the value of the parameter to determine which servlet is going to run
String selectAnimal = request.getParameter("selectAnimal");
if (selectAnimal.equals("SelectAnimalServlet")){
getServletContext().getNamedDispatcher("/SelectAnimalServlet")
.forward(request, response);
//for testing
System.out.println("Request forwarded to " + selectAnimal + " servlet");
}
SelectAnimalServlet code:
try
{
HttpSession session = request.getSession(true);
session.getAttribute("currentSessionUser");
List<AnimalSelectBean> beans = DAO.getAnimalList();
request.setAttribute("beans", beans);
request.getRequestDispatcher("CheckAnimal.jsp").forward(request, response);
}
Now when i run that it's not working for some reason, if i change the link to SelectAnimalServlet directly the code works any idea how to solve this ?
Edit:
Here is my web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:javaee="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<servlet>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>content.LoginServlet</servlet-class>
</servlet>
<servlet>
<servlet-name>UpdateAnimalServlet</servlet-name>
<servlet-class>content.UpdateAnimalServlet</servlet-class>
</servlet>
<servlet>
<servlet-name>SelectAnimalServlet</servlet-name>
<servlet-class>content.SelectAnimalServlet</servlet-class>
</servlet>
<servlet>
<servlet-name>Relay</servlet-name>
<servlet-class>content.Relay</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>SelectAnimalServlet</servlet-name>
<url-pattern>/SelectAnimalServlet</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>UpdateAnimalServlet</servlet-name>
<url-pattern>/UpdateAnimalServlet</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/LoginServlet</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Relay</servlet-name>
<url-pattern>/Relay</url-pattern>
</servlet-mapping>
</web-app>
also I changed:
getServletContext().getNamedDispatcher("/SelectAnimalServlet")
.forward(request, response);
to:
response.sendRedirect(response.encodeRedirectURL(selectAnimal));
and still the same thing blank webpage with http://localhost:8080/oosd/Relay?selectAnimal=SelectAnimalServlet link

getNamedDispatcher expects a servlet name; you're providing it with a servlet URL.
Either use the name, or use getRequestDispatcher with the URL.
Since you're forwarding, the URL will not change--there is no redirect response sent back to the browser on a forward. The contents of the forward are written directly to the original response.
Now that you're forwarding, you need to redirect to the URL, not just the name of the servlet.
What does the servlet you redirect to do for output?
I don't believe your parameter naming convention makes any sense. The parameter shouldn't be named the same as a servlet name; the parameter should be something like "command" or "select". You would then use the command parameter value to look up the URL of the servlet. Or, in your case, just prepend a /, and you're done. There's no need to do any if/else comparisons.