What is the use of init-param tag? in web.xml reagarding servlet and jsp?
<servlet>
<servlet-name>sonoojaiswal</servlet-name>
<jsp-file>/welcome.jsp</jsp-file>
<init-param>
<param-name>dname</param-name>
<param-value>sun.jdbc.odbc.JdbcOdbcDriver</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>sonoojaiswal</servlet-name>
<url-pattern>/welcome</url-pattern>
</servlet-mapping>
</web-app>
We can pass parameters to our servlet from the web.xml file using init param's. Here's a small example.
web.xml:
<servlet>
<description></description>
<display-name>Test</display-name>
<servlet-name>Test</servlet-name>
<servlet-class>servlets.Test</servlet-class>
<init-param>
<param-name>dname</param-name>
<param-value>sun.jdbc.odbc.JdbcOdbcDriver</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>Test</servlet-name>
<url-pattern>/Test</url-pattern>
</servlet-mapping>
Servlet:
PrintWriter printWriter = response.getWriter();
printWriter.println(getServletConfig().getInitParameter("dname"));
Output:
You will find an excellent answer by informatik01 on this subject here.
You can see that init-param is defined inside a servlet element. This means it is only available to the servlet under declaration and not to other parts of the web application.
You can use that particular parameter in only this Servlet not in others.
you can access it by ServletConfig object also
servletConfig.getInitParameter("dname");
They are called Servlet init parameters (defined in element)
Servlet init parameters are defined within the element for each specific servlet.
They are specific to each servlet.They are available in the init method of the servlet as arguments. this will be used for initial loading of values in the servlet.
Related
I have a confusion regarding the structure of the web.xml for the servlet mapping, I don't have any problem by executing it but I am trying to figure it how why we have such a pattern in the deployment descriptor.
<web-app>
<servlet>
<servlet-name>Servlet1</servlet-name>
<servlet-path>foo.Servlet</servlet-path>
</servlet>
<servlet-mapping>
<servlet-name>Servlet1</servlet-name>
<url-pattern>/enroll</url-pattern>
</servlet-mapping>
</web-app>
Now as far as my understanding whenever a request is comes for url-pattern "/enroll", servlet container is going to match the servlet-name with the url-pattern and will try to find the corresponding servlet-path and will forward the control to foo.Servlet. so basically there would be two passes one for finding servlet-name and another for servlet-path, my question is if container is designed to work in the following way
<web-app>
<servlet>
<servlet-name>foo.Servlet</servlet-path>
<url-pattern>/enroll</url-pattern>
</servlet>
</web-app>
what would be the drawback if we use the following approach. Wouldn't that be more efficient and the response time would be fast.
It allows servlets to have multiple servlet mappings:
<servlet>
<servlet-name>Servlet1</servlet-name>
<servlet-path>foo.Servlet</servlet-path>
</servlet>
<servlet-mapping>
<servlet-name>Servlet1</servlet-name>
<url-pattern>/enroll</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Servlet1</servlet-name>
<url-pattern>/pay</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Servlet1</servlet-name>
<url-pattern>/bill</url-pattern>
</servlet-mapping>
It allows filters to be mapped on the particular servlet:
<filter-mapping>
<filter-name>Filter1</filter-name>
<servlet-name>Servlet1</servlet-name>
</filter-mapping>
Your proposal would support neither of them. Note that the web.xml is read and parsed only once during application's startup, not on every HTTP request as you seem to think.
Since Servlet 3.0, there's the #WebServlet annotation which minimizes this boilerplate:
#WebServlet("/enroll")
public class Servlet1 extends HttpServlet {
See also:
How do servlets work? Instantiation, sessions, shared variables and multithreading
Difference between each instance of servlet and each thread of servlet in servlets?
Our Servlets wiki page
I have a Dynamic Web application, and because of the requirements, I am specifying two types of servlet mappings in the web.xml file; Faces Servlet & Jersey(JAX-RS implementation).
My problem is, that if I try to use '/' as the base url-pattern in the Jersey configuration, then the resources of Faces Servlets stop working, i.e., nothing happens if I make REST call to those resources, otherwise everything works fine if I place something like'/rest/' in the Jersey Configuration. My web.xml file looks like this:
<!-- Jersey -->
<servlet>
<servlet-name>Jersey REST Service</servlet-name>
<servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
<init-param>
<param-name>jersey.config.server.provider.packages</param-name>
<param-value>com.saf.web.v2.beans</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>Jersey REST Service</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
<!-- Faces Servlet -->
<servlet>
<servlet-name>Faces Servlet</servlet-name>
<servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
<load-on-startup>100</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>Faces Servlet</servlet-name>
<url-pattern>*.xhtml</url-pattern>
</servlet-mapping>
Is there a way to specify the Jersey mapping so there is nothing in the url-pattern but '/*' and Faces Servlet resources also work fine at the same time.
Thanks!
If you define that Jersey should serve all requests (this is what /* means) the Faces Servlet doesn't have a chance any more. So in general: There is no such way.
Maybe you could work around this be mapping Jersey to /rest and writing an own Servlet mapped to /* which dispatches to one of the other servlets. I would not recommend that.
I had the same problem but I fixed it by using
/rest/*
for jersey's servlet
and other part of application can have any other url-pattern, as in your case it is *.xhtml for JSF's servlet.
I want to redirect all connections (/*) to a specific servlet, except a specific file (someFile.xml).
I have the following section in web.xml:
<servlet-mapping>
<servlet-name>someServlet</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
How can I modify it so that /someFile.xml will not be mapped to this servlet.
If I cannot do it using web.xml, is there some other way?
You can create a Servlet and map it to receive /someFile.xml.
<servlet-mapping>
<servlet-name>someServlet</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>SomeFileServlet</servlet-name>
<url-pattern>/someFile.xml</url-pattern>
</servlet-mapping>
In this way all request except /someFile.xml will go to someServlet and request for /someFile.xml will go to SomeFileServlet.
**/* mapping in web.xml it answers all requests except other path mappings.**
I have a confusion regarding the structure of the web.xml for the servlet mapping, I don't have any problem by executing it but I am trying to figure it how why we have such a pattern in the deployment descriptor.
<web-app>
<servlet>
<servlet-name>Servlet1</servlet-name>
<servlet-path>foo.Servlet</servlet-path>
</servlet>
<servlet-mapping>
<servlet-name>Servlet1</servlet-name>
<url-pattern>/enroll</url-pattern>
</servlet-mapping>
</web-app>
Now as far as my understanding whenever a request is comes for url-pattern "/enroll", servlet container is going to match the servlet-name with the url-pattern and will try to find the corresponding servlet-path and will forward the control to foo.Servlet. so basically there would be two passes one for finding servlet-name and another for servlet-path, my question is if container is designed to work in the following way
<web-app>
<servlet>
<servlet-name>foo.Servlet</servlet-path>
<url-pattern>/enroll</url-pattern>
</servlet>
</web-app>
what would be the drawback if we use the following approach. Wouldn't that be more efficient and the response time would be fast.
It allows servlets to have multiple servlet mappings:
<servlet>
<servlet-name>Servlet1</servlet-name>
<servlet-path>foo.Servlet</servlet-path>
</servlet>
<servlet-mapping>
<servlet-name>Servlet1</servlet-name>
<url-pattern>/enroll</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Servlet1</servlet-name>
<url-pattern>/pay</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Servlet1</servlet-name>
<url-pattern>/bill</url-pattern>
</servlet-mapping>
It allows filters to be mapped on the particular servlet:
<filter-mapping>
<filter-name>Filter1</filter-name>
<servlet-name>Servlet1</servlet-name>
</filter-mapping>
Your proposal would support neither of them. Note that the web.xml is read and parsed only once during application's startup, not on every HTTP request as you seem to think.
Since Servlet 3.0, there's the #WebServlet annotation which minimizes this boilerplate:
#WebServlet("/enroll")
public class Servlet1 extends HttpServlet {
See also:
How do servlets work? Instantiation, sessions, shared variables and multithreading
Difference between each instance of servlet and each thread of servlet in servlets?
Our Servlets wiki page
The following code accesses a servlet's name: servletConfig.getServletName().
Can I access a servlet's URL pattern in a similar way?
An excerpt from web.xml:
<servlet-mapping>
<servlet-name>This is the servlet's name</servlet-name>
<url-pattern>/this-is-its-url-pattern/*</url-pattern>
</servlet-mapping>
In Servlet 3.0 (or Java EE 6) spec exist something:
http://docs.oracle.com/javaee/6/api/javax/servlet/ServletRegistration.html
You can get a ServletRegistration using ServletContext.html#getServletRegistration.
Nothing is available in the Servlet API. Either parse the web.xml yourself, or duplicate it as an <init-param> of the servlet wherein you'd like to access it.
<servlet>
<servlet-name>servlet</servlet-name>
<servlet-class>com.example.Servlet</servlet-class>
<init-param>
<param-name>url-pattern</param-name>
<param-value>/servlet</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>servlet</servlet-name>
<url-pattern>/servlet</url-pattern>
</servlet-mapping>
This way it's available by servletConfig.getInitParameter("url-pattern").