I want to look for extension jars in a predefined directory and examine their manifest. Those which match should be loaded, those which do not - should be unloaded.
Now, I can do it a primitive way - mandate that each extension pass the name of its bootstrapper on the command line and then for each jar found in the directory try and load any of the given bootstrapper types. Something like this:
java -jar myapp.jar --pluginDir=c:/a/b/c --exts="classA;classB;classC"
Then myapp would iterate over all the files inside the pluginDir and try to load each of classA, classB or classC. Once a classX is successfully loaded, it is removed from the list. The search stops when either all the extensions are found and loaded or there are no more jars in the plugin dir.
A slightly more javaish approach seems to be writing something in the manifest of extension jars and check the manifest of each found jar.
Can anyone show a working code snippet of this approach or of anything better, if there is?
EDIT
A quote from the postgre JDBC driver README file (see https://stackoverflow.com/a/12480373/80002):
INSTALLING THE DRIVER
To install the driver, the postgresql.jar file has to be in the classpath.
ie: under LINUX/SOLARIS (the example here is my linux box):
export CLASSPATH=.:/usr/local/pgsql/share/java/postgresql.jar
There is ServideLoader class for this purpose. JDBC drivers are built on this principle. Hope, it helped.
Related
Uploaded a jar file from my computer to a server and tried to run it. When I run it I get java.lang.NoClassDefFoundError and it seems to be related to the twitter4j jar that my main method depends on.
However, I have this jar file in my libraries so shouldn't this be included when I build my code in to a jar? Here's a pic in case it helps.
is the error that I'm getting. (can't upload a pic just yet.
Not sure what this has to do with twitter, but anyway, the issue is that you do not have the correct class files. In other words, when you are running your fat JAR in the command prompt, you do not have any libraries exported with it (Or if you do, you don't have that specific one).
Sometimes such an error can be because there is an incorrect version of java, however that is not the case here since java has got no "twitter" packages or classes in it.
Using something like JarSplice would fix this.
Assuming you did not package the twitter4j classes inside your application jar, you need to tell Java where it can look for classes that are not inside your application jar. You typically use the classpath flag for that. In your case, it should look something like
java -cp /tmp/twitter4j.jar -jar /tmp/myapp.jar
An alternative would be to package all twitter4j's classes inside your application jar. This is called a 'fat' jar. How to make one depends on how you build your application jar.
The JAR file that you are trying to use needs to be in the classpath. This can be done by using the -cp attribute from the command line. However, when using java -jar, you cannot use the -cp attribute.
To get around this, you can do the following:
java -cp /tmp/myapp.jar;\path\to\external.jar com.example.package.MyClass
where MyClass has the main() method defined.
Alternately, you can specify jar files on the classpath using the manifest.mf file. See http://docs.oracle.com/javase/tutorial/deployment/jar/manifestindex.html for details.
I am fairly new to Linux, I am trying to set my jar files for OJDBC in my classpath but so far have not found any good examples for a beginner such as me.
I will list the my paths for Jar file below. Can someone provide me with example or how to step by step set my class path with the commands. I would really appreciate it. I would like to set this path in my project which I am using it in.
Jar file:
/home/ssingh/Downloads/oracle.jar
Project:
/opt/savi/Workspace/SgRecc/bin/PerVal.class
Setting up the Class Path
To use the driver, the JAR archive named postgresql.jar if you built from source, otherwise it will likely be (named with the following convention: postgresql-[server version].*[build number].jdbc[JDBC version]*.jar, for example postgresql-8.0-310.jdbc3.jar) needs to be included in the class path, either by putting it in the CLASSPATH environment variable, or by using flags on the java command line.
For instance, assume we have an application that uses the JDBC driver to access a database, and that application is installed as /usr/local/lib/myapp.jar. The PostgreSQL™ JDBC driver installed as /usr/local/pgsql/share/java/postgresql.jar. To run the application, we would use:
export CLASSPATH=/usr/local/lib/myapp.jar:/usr/local/pgsql/share/java/postgresql.jar:.
java MyApp
I'm a little confused by this error. I'm new to Java and the error seems pretty self explanatory, but I've checked my paths (even defined my own) and it still fails to find this library. Is there something I'm doing wrong? See directory screenshot and error screenshot below:
UPDATE
UPDATE 2
If I create a new NetBeans project this works fine. Same code and everything. If I create new IntelliJ project I get this error above. I must be missing something in IntelliJ
UPDATE 3
Found the solution. Adding dependencies is a bit different in IntelliJ. Thanks all for the help.
http://www.jetbrains.com/idea/webhelp/configuring-module-dependencies-and-libraries.html
Obidisc4j is a .jar file. You just dont see its extension in the explorer.
Regular jar files are not loaded by System.loadLibrary. They are automatically loaded by the JVM's classLoader.
You are using a native library. It doen't matter if that library is in the classpath. There are 4 ways you can make the Java runtime load your shared library at runtime:
Call System.load to load the .so from an explicitly specified absolute path.
Copy the shared library to one of the paths already listed in java.library.path
Modify the LD_LIBRARY_PATH environment variable to include the directory where the shared library is located.
Specify the java.library.path on the command line by using the -D option.
Seems like your application is trying to find out a obidisc4j.dll (for Windows) or obidisc4j.so (for Linux). The file must be present on the PATH (but not the classpath). If you are not sure what PATH is your Java application searching in, you can write the following statement, before the point where the exception takes place, to find out the PATH.
System.out.println(System.getProperty("java.library.path"));
This will tell you about the paths where your DLL or SO file should be placed. You just need to place the file in ONE of those N-paths.
This issue is related to running a Java program (jar) dependent on thirdparty jar library even after setting classpath and trying so many other methods by reading articles in Internet.
I want to use a thirdparty Pack1.jar (it is not a part of jvm) as dependency of my programme.
I do not know where the Pack1.jar file could be in the deployment machine and I want the deployer to specify the path for the thirdparty libraries
I have tried the following alternatives in vain
Setting the java.class.path programatically
String class_path = args[0];
System.setProperty("java.class.path",class_path);
Here I am assuming that deployer would supply the classpath as first argument while running the program
Setting the CLASSPATH env_var to locate the thirdparty directory
While running, using the classpath option
java -classpath /path/to/Pack1.jar -jar Pack2.jar
I think this would not work because documentation says that classpath is ignored when program is run with "java -jar"
Setting the java.ext.dirs programatically.
Setting the java.library.path programatically.
I do not want to specify the Class-Path in manifest because that takes only relative path and I do not know where the thirdparty library would be kept in deployment machine
But I am unable to get the jar running.
How can I fix this problem any help please.
Go for option 3. Put both jars on the classpath like this:
java -classpath '/path/to/Pack1.jar:/path/to/Pack2.jar' com.packagename.yourclassname
Note, that this is for Linux. on Windows, you would separate classpath elements with semicolons:
java -classpath "/path/to/Pack1.jar;/path/to/Pack2.jar" com.packagename.yourclassname
http://en.wikipedia.org/wiki/Classpath_%28Java%29
You can use Pack2.jar without running it using -jar--put it on the classpath and call the entry point listed in its manifest file.
I usually wrap that up in a launcher script to avoid those kinds of problems, and allow jar paths to be set using an argument.
Name the secondary JAR(s) in the Class-path entry of the Manifest.MF of the main JAR file, and use java -jar.
Your objection to this technique doesn't make sense. If you supply and deploy the secondary JAR files, as you should, you have the same degree of control over their location as you do over that of the major JAR file. It doesn't matter where else the user may have copies of them.
this will sound silly but i am executing my code from command prompt and have to use a jar in my class.
I have placed my jar in lib folder of JDK..
but i am still getting error of file not found
any explanation??
EDITED : guys tried all but still not working
EDIT 2 :i am trying to work as was told by this link i am using js-1.6R5.jar
Edit 3 : i undestand all the things you ppl have told but nothing working for me.. pls give me a link to upload my example that i can share with you all.
Edit 4 : i am fed up by setting classpaths but its not working... i have SDK installed in my system, do i need an extra JDK to run my programs from command prompt??
You need to add the jar to the class path by doing the following...
java -classpath D:\myprogram;D:\myprogram\lib\supportLib.jar org.mypackage.HelloWorld
Please see Wikipedia - Classpath_(Java)
You can place it anywhere, as long is you include it in your classpath. See Setting the Class Path for how to include jars in the classpath.
Have in mind that adding something in the JDK lib is almost never a good idea.
You can make a lib folder in your application's directory and put jar files there, then make your application find them by adding lib to your application's classpath.
And, don't put your jar files in JDK's lib folder. It's not good practise.
You need to let Java know that you want to include the jar in your classpath (the list of folders and jars it checks for classes). One way to do this is with the -cp command line argument, something like
java -cp ".;pathToMyJar\myJar.jar" MyClass
Another is to edit the CLASSPATH environment variable in your OS to include your jar.
A simple solution will be to place the jar fiel inside the windows folder if you are doing it in a Windows machine.
Unfortunately your question contains a lot of question signs and few information.
If you are using java.io.File to open jar as a regular file this jar should not be in lib directory. You just have to provide correct path in file system.
If however you are just trying to use jar as a part of your application it should be in classpath. Use either command line java -cp myjar.jar MyMainClassor put full path to this jar to global environment variableCLASSPATH`.