I'm having trouble wrapping my head around how to use servlets properly
I've set up a postgres database, and downloaded a JDBC driver for it.
What I want to have is my webpages post to the servlet, and the servlet get info from the database. I understand how to code everything (eg add library for driver, open connections, execute queries), but I think I'm lacking knowledge in how to set up the file structure.
I have the postgresql database running on pgAdmin. Do I also need to have a server running to make the servlets work as well? Can't I just make a web.xml file that maps to the servlets, and open the webpages to use the website? If I run the project through an IDE with a server running (glassfish) everything works. If I close the IDE and go to open the webpages on my browser again, I get 404's whenever I submit to a servlet.
Can someone give me a bit of guidance on the big picture of how everything is supposed to interact (with details on servers please). I've been searching the web and I havent found anything that explains the big picture very well.
Thanks
A Java web application is a set of files obeying a well-defined structure, and which can be packaged in a war file.
This web application is deployed into a server (also called container), which understands the file structure, listens to HTTP requests, and calls the appropriate servlet of the appropriate deployed web application when it receives one.
And of course, if you shut down the server, nothing listens to the HTTP requests anymore, so you won't get any response.
You could read the Java EE tutorial for more explanations.
Related
I created my first Java EE application (GWT + Hibernate). I want deploy my application on a Tomcat web server.
Could you give me a step by step tutorial?
You can start with Google App Engine + GWT tutorial if you are trying out deploying into Google Cloud - https://developers.google.com/web-toolkit/doc/latest/tutorial/appengine
This question is massive so I will try to bring it down to some steps that need some research to implement.
1st. You created an application using GWT and Hibernate. That means that you need some kind of a web server that understands java and can re-write the logic from java to javascript (for the clientside), and also connect to the database on the serverside and retrieve the data for the client.
This web server is tomcat so what you need is:
A computer that will work as a server. This could be your own machine or some server you can buy as a hosting solution. Buying something like this requires research and effort on your part and cannot be explained here.
A version of Tomcat or Resin or any other web server that understands java
A domain name. These can be bought from sites like this one, but there are some free ones around the web. They require static ips that is you cannot use them from a home line that changes ips. Even without a domain name you can host your site on the server but you need to access it by writing the machine's ip instead. - optional - A temporary solution would be to use some kind of dynamic dns service on your router.
After having set up tomcat (you might want to give port 80 to tomcat) and the server you can host your application by uploading the war file. You can make a war file from gwt by following the instructions here
To upload the war file you can use the tomcat manager interface, or you can connect to the server and place it manually in the folder used for the web applications.
I know that each step propably needs as much if not more explanation by I hope I cleared the area a little bit here.
Our lab has a single machine that is open to http connections from outside. However, this machine is quite weak (little memory, slow CPU). We have other machines that are much stronger, but they are behind a firewall and cannot be accessed from outside the lab.
I am writing a GWT app whose server is very demanding. Is it possible to install the server on a strong computer, and the client on the weak compuer, and have them connect using RPC? I assume it requires some changes in the web.xml file, but what exactly?
Theoretically I can just wrap the demanding part in a separate TCP/IP server, and have the GWT server contact it, but I would like to know if it is possible to do directly in GWT.
The GWT client is downloaded from the server and runs inside a Web browser as javascript code. I don't quite understand what part of the GWT app you would want to run on a separate server.
If your GWT servlet (the RPC service implementation) is accessing external resources, like a database or Web services, you could move those resources to a separate server.
Another option is to install a reverse proxy on the "weak" server that would forward specific requests to a stronger server behind the firewall. The proxying could be done by Apache (httpd) on the "weak" server (using mod_proxy). Then Tomcat would only need to be installed on the stronger machine, and would take care of most of the processing.
I have tried to do this but was only successful in splitting a GWT project into 3 parts (Client, RPC, Server) as eclipse projects. In the end you are going to end up with 1 big WAR file and it'll be deployed in one place (unless someone else was successful at really separating the code.)
A solution you can do is to set up another server that will do all the server side processing (your strong machine) and have the GWT servlets act like a proxy. They accept the requests from the client and forward the data to another server for processing. Then wait for the response.
How you do it is up to you. You could use web-services, direct socket connection, JMS ..etc.
Depends on your setup.
GWT ACRIS- Please see this link.
EJB - One approach could be to keep business objects in remote machines as EJBs and your servlets accessing them over RMI/JNDI.
Spring - Another simple way to do it is with Spring Remoting. See this link.
I have a few questions about deploying my .ear file (was provided to me, the file itself should not be the problem). I set up jBoss application server jboss-6.0.0.Final and was able to run a simple hello world app to ensure the server was functioning properly.
I was told to place the .ear file in /server/default/deploy so I did. When I ran jboss (through /bin/run.bat) I got no errors related to deploying the ear file.
Question
Is this all the software I need (jBoss)? Do I also need something like Apache or tomcat?
The .ear file contains RESTful service calls that should return xml. Will these be deployed (accessible through a jQuery ajax call after the server (jboss/bin/run.bat) is executed?
Currently when I try to make the calls, the resources do not seem to exist.
Thanks in advance for taking the time to help.
JBoss AS ships with an embedded Tomcat as a servlet container so you really don't need that anymore. Apache Web Server is NOT required for your .EAR to be deployed properly.
To answer your questions
No other software is needed to deploy the EAR. You simply copy your EAR file to deploy directory (which you have rightfully done so).
If your EAR contains RESTFul services, they will be deployed and you can access them using any client including jQuery or even a simple browsers. The trick is to know the access URL to the RESTFul services.
If you have difficulty identifying the URL for accessing your RESTFul services please refer [1] for more information.
Hope this helps.
Good luck!
[1] https://docs.jboss.org/author/display/AS7/JAX-RS+Reference+Guide
I can answer the first question. You need apache if you want to serve static content or you need to isolate the traffic (say keep apache in the dmz and then use apache to proxy traffic to the internal jboss servers). tomcat is bundled along with jboss, so you do not need it.
I'm thinking about an application where in some cases both client and server would run on customer's computer. Concerning the client's resource usage I've found this question, concerning the general disadvantages of GWT I've found this, but I can't find anything about the overhead of the server part. I need no application server there, anything capable of running the server part of GWT would do.
What is needed to run the server part of GWT and how many resources it consumes?
If you use a ServiceImpl w/ your GWT app, you need to deploy it into a servlet container, like Tomcat or Jetty (or many others). Otherwise, it can be deployed on any web server, as it will only consist of javascript, HTML, and CSS.
I'm trying to call a web service in my back end java code when it's
running in hosted mode. Everything loads fine, the GWT RPC call works
and I can see it on the server, then as soon as it tries to call an
external web service (using jax-ws) the jetty falls over with a
Internal Server Error (500).
I have cranked the log all the way up to
ALL but I still don't see any stack traces or cause for this error. I just get one line about the 500 Error with the request header and response.
Does anyone know if the internal jetty keeps a log file somewhere, or
how I can go about debugging what's wrong?
I'm running GWT 1.7 on OS X 10.6.1
Edit: I know that I can use the -noserver option, but I'm genuinely interested in finding out where this thing lives!
From the documentation:
You can also use a real production
server while debugging in hosted mode.
This can be useful if you are adding
GWT to an existing application, or if
your server-side requirements have
become more than the embedded web
server can handle. See this article on
how to use an external server in
hosted mode.
So the simplest solution would be to use the -noserver option and use your own Java server - much less limitations that way, without any drawbacks (that I know of).
If you are using the Google Plugin for Eclipse, it's easily set up in the properties of the project. Detailed information on configuration can be found on the official site.
Edit: you could try bypassing the Hosted Mode TreeLogger, as described here: http://blog.kornr.net/index.php/2009/01/27/gently-asking-the-gwt-hosted-mode-to-not):
Just create a file called
"commons-logging.properties" at the
root of your classpath, and add the
following line:
[to use the Log4j backend]
org.apache.commons.logging.Log=org.apache.commons.logging.impl.Log4JLogger
[to use the JDK14 backend]
org.apache.commons.logging.Log=org.apache.commons.logging.impl.Jdk14Logger
[to use the SimpleLog backend]
org.apache.commons.logging.Log=org.apache.commons.logging.impl.SimpleLog
Edit2: the trunk of GWT now also supports the -logfile parameter to enable file logging, but it probably won't help in this case, since the problem lies in the way the Hosted Mode treats the exceptions, not the way it presents them.