Technical FAQ: General questionsFAQ Index
I upgraded to JDK 1.1.6 on Win 95/NT. How come my application no longer works?
In JavaSoft JDK 1.1.6 the Symantec JIT is enabled by default. Unfortunately, the JIT included in the Win32 download has some problems. There is an updated JIT available from the Javasoft web site. You will need to register with the Java Developer Connection to access this, but it is free.
Alternately, you can run without the JIT by invoking java with the command line option
$ java -Djava.compiler=none
I am experiencing problems trying to connect from behind a firewall/proxy installation at client sites. Is there any way to configure WebLogic to use a SOCKS proxy?
You can configure a java.net socket to use SOCKS by setting a Java system property. For details, see How do I make Java work with a proxy server?. Once the property is set, WebLogic's socket connections will use the SOCKS proxy.
We recently installed a WebLogic Server, and found that it seems to take 15-30 seconds to respond to connection requests, even when there is no significant load. How can I speed up connection delays?
Connection delays are often caused by DNS problems. WebLogic performs a reverse lookup on the hostname from which a new connection is made. If the DNS reverse lookup is not working properly because the connection is coming from some kind of proxy server, it could be responsible for the delay. You might want to work with your system administrator to determine whether DNS and the third-party networking software are working properly. Try writing a simple server program that performs a reverse lookup on any connection made to it. If that lookup is delayed, then you know that the proxy server is the source of the problem.
What about the June, 1998 SSL-related security bulletin?
On June 16, 1998, RSA released a security bulletin (#7) which notified its licensees about a vulnerability in the PKCS1 standard. This standard is used in SSL as part of the initial key exchange. It advised its licensees on measures to take to ensure security on systems that use RSA.
The vulnerability is purely theoretical. It consists of distinguishing between two kinds of error responses. To exploit it, an attacker would have to carefully generate and analyze on the order of one million error responses from an SSL server.
WebLogic uses RSA in its SSL implementation. Based on the suggested fix from RSA, WebLogic changed how encoding failures are handled so that error messages are completely uniform. The changes are included in WebLogic release 3.1 and later. For Tengah versions 2.5.4 through 3.0, a patch for a single class (weblogic.security.SSL.ClientKeyExchange) is available.
Only SSL servers -- in this case, WebLogic listening for SSL login requests -- are vulnerable. If you are using HTTP with WebLogic to proxy SSL requests to another server, there is no need to download the patch.
How to install the patch:
You do not support 1.0.2 anymore?
In order to assure compatibility when running applets, we recommend that you upgrade your browsers to either Netscape Communicator 4.0.3 or later or Microsoft Internet Explorer 4.0 or later. Alternately, you can use the Java Plug-in, available free from JavaSoft, which automatically updates the browser JVM.
You asked me to send you a "logfile." What exactly do you mean?
You can generate a stacktrace in your code by inserting the following line of code after you catch an Exception "e".
There are several examples of using the printStackTrace() method in the code examples in the examples included with the distributions. All of the source code for the examples is also available on our website.
Will using a JIT make my Java application run faster?
A Just-In-Time compiler will make some Java applications run faster. A JIT works by storing generated machine code in memory and reusing it when possible. For instance, if you execute the same operation 1000 times in a loop, a JIT will improve performance of this operation since the code will only be generated once. Applications with a lot of native methods will not see as much performance improvement as pure-Java applications.
If you use a JIT, you may want to turn off the JIT during debugging to facilitate stacktracing. If you are doing performance testing with a JIT, make sure that you execute the same test several times in the same invocation and then throw away the first result to get an idea of how long the transaction will take when your application is running in a steady state. The first time the code is executed, your test will take longer (the "code generation hit").
Also see news about the JIT in JDK 1.1.6.
What do you mean by "two-tier" and "multitier" drivers?
What do you mean by "two-tier" and "multitier" JDBC drivers?
Two-tier drivers -- such as jDriver for Oracle -- call the vendor libraries for each specific database. Because the vendor libraries are not written in Java, a two-tier driver uses "native methods." This requires the vendor's database libraries, (.dll or .so) to be installed on the computer running the Java code so that the JVM can call into the libraries.
With multitier (also called "three-tier") drivers, an intermediate application server sits between the JDBC driver and the database. WebLogic's multitier JDBC driver, WebLogic JDBC, is pure-Java and doesn't use any native methods. That means that it requires no client-side installation of vendor libraries. A client application that uses WebLogic JDBC connects to the intermediate application server -- the WebLogic Server -- and the application server connects to the database on behalf of the client. When you use WebLogic JDBC, your clients do not need vendor libraries. Only one copy of the vendor library is required, along with a two-tier JDBC driver, on the computer running the WebLogic Server.
For more about this topic, read the whitepaper, Choosing a JDBC driver.
I'm having trouble with Java -- What do I do?This is really a whole set of questions that our support engineers are sometimes asked. We are very happy to help you with problems you are having with our software, but we can only offer you directions to some other resources for problems like these:
My program will not work. Can you help me debug it?
If the problem you are having is not directly related to our software, we suggest that you use a Java development tool that helps you with debugging, and that you invest in some books/training to help you learn Java. There are many ways to build debugging into your program, and getting good training in Java programming is a good start to understanding how to do this.
I'm taking a class and I need help learning Java.
There are a lot of books and online references to Java. A good starting place is at the JavaSoft website documentation index, which has links to whitepapers and the Java Tutorial. You can find books on Java at any of the major online book shopping sites.
Where do I get the JDK?
Start at the JavaSoft website. Many platform vendors provide an optimized version of the JDK for their computers. See our Platform support page for information about specific JDKs that we have tested and certified for use with WebLogic software.
How do I set up my CLASSPATH?
Setting up your CLASSPATH is pretty easy, once you understand what you are doing. Check our administrators guide, Setting classpath.
When I try to run an example, it doesn't work.
Usually problems with examples are related to your environment. Here are some troubleshooting hints:
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