How do I check if a Class is an instanceof another Class without initializing it?

Illustration: Cathy Wilcox

We had a recent security audit and a question was posed about how to check a Class without doing an instanceof. This turned out to be a great learning experience. There were a couple of issues that needed to be resolved, first we were loading a Class by passing in its name using something similar to the line below: This will load the Class, but from here how do we check that it is an instanceof without instantiating it?
This can be solved by using isAssignableFrom(Class clazz) as shown below. In this case we are checking if SolientGreen is Green. Some of you will find the moral paradox of being "Green" with Soilent Green.
The second issue is a more potential security problem. How do we load the Class without initializing it. If the Class has a static initializer, the code is executed when the class is loaded. Alas, this is handled by using a variation of Class.forName(String name, boolean initialize, ClassLoader loader) which takes a boolean to determine if the class should be initialized, and a ClassLoader if you want to specify a specific loader.

Finally, we can check the Class like this: When this is run, you will not see the message. Very nice indeed!

So here is the remaining code for education and entertainment:
The code for the project can be downloaded from Bitbucket here: assignable

Lambda Expressions on Java SE 6

Introduction

I attended a talk at JavaOne 2013 on Expression Language 3.0. It was a great talk by Ed Burns and Kin-man Chung about EL. EL 3.0 has been modular for a while, and can operate independently of the EE platform. I knew that, but this was a siren call reminder of that fact. During the talk, I asked a number of questions and for clarifications. One interesting clarification was that EL 3.0 was compiled using Java 7. This was following a discussion of the fact that it supports Lambda expressions. Wait... it uses Lambda expressions from Java 8 and is compiled using Java 7. I asked could it be compiled on Java 6. Kin-man Chung, the specification lead, told me that with some minor changes; "it should?" I took that as a challenge to try. I was successful and now I can do Lambda expressions on JDK 6.

When I mentioned that I was using this technique for Java 6 on Twitter, Michael Graciano pointed out that +Adam Bien  had done something similar for Java 1.7. I am not sure if great minds think alike, or fools seldom differ on this one, but his article is a very cool read too.

@jyeary @RichardWarburto you mean something like this? http://t.co/CdaR29wJBw
— Michel Graciano (@mgraciano) October 2, 2013

Technical Details

The easiest way to try it out for yourself is to download the compiled version here: javax.el-3.0.0-custom.jar
 
If you want to create your own, then follow these easy steps.

1. Download and install Java CC 6.0
2. Download Java EL project using NetBeans Team Server on Java.net, or using Subversion: https://svn.java.net/svn/el-spec~source-code/tags/javax.el-3.0.0
3. Open the impl directory and modify the build.xml file to point to your Java CC 6.0 directory, for example:
   
4. Change the pom.xml to source and target level 1.6
   
5. Change the version in the pom.xml so that it is distinguishable from the RI.
   
6. Execute a mvn clean
7. In the impl directory, execute ant. This will compile the parser code for EL.
   Note: This is a very important step!
8. Modify the org.glassfish.el.test.ELProcessorTest, and remove all of the try with multicatch, and diamond operators.
9. Execute mvn clean install.

If you were successful, you will have a version of EL 3.0 that will run on Java SE 6.

You can test your code using some of the examples found in the references below, or using the sample code snippet that uses some of the code from the references.

App.java

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References

• THE HIDDEN JAVAEE 7 GEM - LAMBDAS WITH JDK 1.7
• Java EE 7 Delivers Expression Language Enhancements
• Standard Deviation: An Illustration of Expression Language 3.0 in Servlet Environment
• Expression Language Specification
• JSR 341: Expression Language 3.0

Java 6 File Monitoring Example

I was asked today how you would monitor a file for changes using Java 6. Since Java 7 has added some great File handling features that I use, it was a reminder that not everyone is so lucky to use Java 7. I remembered an example from Geosoft (I remembered it because I liked the name). I went looking and I found their example code FileMonitor.java. It is a simple and elegant solution to monitoring files and directories for changes.

This is by no means a complete example, but does show a simple technique.

Java Tip of the Day: Converting an InputStream to a BufferedImage

I was looking for a standard way using the JDK to convert an InputStream into a BufferedImage as part of a JUnit test. The solution was quite simple using ImageIO.

Code

JDK7 vs. JDK 6 File Monitoring

One of the really nice advancements, or features of Java 7 is the WatchService. This feature takes advantage of the OS file event notification facilities where available, or otherwise uses a "primitive" polling mechanism. In my blog article WatchService Using ScheduledExecutorService Example, I show an example of how to use the WatchService along with an ExecutorService to do file monitoring. This is really easy to implement and use.

However, the question of how to do it on JDK 6 was posed to me for those who can't do an upgrade for business reasons. I did a quick Google search to see what was out there. Alas, some of the most popular search results were poor, or really badly implemented solutions. I did come across a nice piece of code done by Pascal Essiembre. I didn't find much more on the developer. I would give a link to his work if I were sure that what I found was him. Pascal wrote the code below which is EPL 1.0 so you are free to use it. I used it to check it out, and it works likely in the same manner as the "primitive" implementation in JDK7. Here is the code unmodified from the form I found. This is very nicely done. Good code lives on. I just wish this were more near the top of the search results.

Thanks Pascal for your code contribution to the Java community.

Exporting Trusted Certificates in Java

I was trying to export some trusted certificates in Java, and I discovered that the default Java keytool will not do it much to my dismay. So I decided to write a little utility class to export the certificates into PEM files from X509 certificates so it would be easier to move them around.

I thought I would clean up my little tool, and share it with the world.

It requires the GlassFish webservices-osgi.jar which is located in the glassfish-3.1.2/glassfish/modules/ directory along with Apache commons-cli-1.2 and commons-io-2.1.

The application takes a couple of command line arguments to work. It has usages, but the project properties also shows all of them in action. You will need to set that up to match your environment in the IDE. Here is an example.

java -jar certificate-manager.jar -f /Applications/NetBeans/jboss-5.0.1.GA/server/default/conf/server.keystore -i "CN=John Yeary, OU=Development, O=Blue Lotus Software, L=Greenville, ST=South Carolina, C=US" -s 4f2ac2cf -p changeit -e

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

The project was developed with NetBeans and GlassFish 3.1.2.

The NetBeans project files can be downloaded here: certificate-manager.zip

TrustedCertificatePEMExportUtility.java

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