JDeveloper 11g Cannot Establish App Server Connection

Very often I see people bump into this error and thought I should make some notes here which might help someone in need.

First of all, I would like to make some inferences from the JDeveloper documentation;

"By default, JDeveloper uses the proxy settings from the default browser on the same machine, adding localhost and 127.0.0.1 to the list of proxy exceptions. If you have problems making connections from JDeveloper, for example, connecting to an application server or a SOAP server that is on the same machine as JDeveloper, you may need to change the proxy server settings you use."

Pre-Requisite:
While trying to establish a connection to the App server from JDeveloper, ensure that the following settings are correct;

1. Weblogic Hostname : resolves to the actual IP address of the server
2. Port: 7001 (default admin server port) or as per your admin port configuration during install. Remember you should only use the admin server port of your WebLogic server here even if you have an architecture where you front end the app server with a HTTP server like OHS
3. Domain: Use the domain name that was created during the WLS configuration

Check 1: Check whether the proxy settings are disabled in JDeveloper. Go to Tools -> Preferences -> Web Browser & Proxy section and ensure that no HTTP proxy server is setup. If already configured, uncheck the check box and click OK

Check 2: Test whether the port 7001 on the WLS host is accessible from the machine where JDeveloper is installed. You can test this with a simple telnet command;

telnet hostname 7001

If this test doesn't succeed then there can be two possible reasons;

1. There can be a network firewall or firewall enabled on the server which blocks this admin port from being accessed from a client machine. If this is the case, then ask your network administrator to open the port. This can be done by adding the port to the ip6tables on the linux server or similar.

2. Do a netstat on the linux server where WebLogic is installed to find out whether the port is open and is available (LISTEN mode). Ensure that your admin server is running when you run this command

eg., netstat -apn | grep 7001

This will show up the ip addresses from which the host can accept requests. Some common causes that I have identified is that the /etc/hosts file contains the ip - hostname mapping as follows;

127.0.0.1          hostname1

When the WebLogic server starts up, it will start all services properly but a closer look at the netstat command reveals that the host accepts connections only from within the server (127.0.0.1). This means that the port is virtually blocked for any requests coming from outside the machine/host itself. To resolve this issue, change the /etc/hosts file entry as follows;

<ip address of host >       hostname1

Now, stop all services and restart the services. This enables all WebLogic ports and accessible from outside the server.