I have a jar file which contains some classes those which i want to use in my project. I am working in command line and not in eclipse.
Please tell me how i should use those classes in the jar file for my project.
Use the -classpath command line option:
javac -classpath library.jar MyProgram.java
And then to run it, specify the classpath again - including where your actual code is:
java -classpath library.jar;. MyProgram
(That's assuming you're using Windows. On Unix use : instead of ; as that's the path separator.)
Jar file is a way to package java classes. To use the classes in the jar file, you need to include the jar in your classpath.
You need to then import the required class(es) in your java code and access them.
Of course you need to know how to use these classes i.e. what public methods etc. they expose.
If these jars correspond to some 3rd party library, you need to check the documentation (maybe on the web) to see how to use the classes.
You just include it to your classpath like this:
java -cp otherclasspath;thejar.jar yourlass
Related
I am looking for a way to run the standard class file as produced by Intellij for hello world, using a gradle build with kotlin-stdlib-1.3.11 as the only dependency.
I know I could make a jar file and run that but that is not the question. That question is already answered in many places, but please do not answer with those solutions as that is not the question I am asking.
The simple class file for 'hello world' needs access to the kotlin-stdlib-1.3.11.jar, and I am looking for a way to run the class file and manually specify jars to use for satisfying the dependencies.
I am making notes for team members on why:
java HelloKt
in folder where the class file is located, should give a NoClassDefFoundError and also looking to then show how manually specifying 'run the class but with the kotlin std lib as well' should then work.
I repeat, I am not trying to just get the program to run. I am trying to show how run the standard library is required to run the class file.
This is about the classpath.
The easy answer is to run kotlin instead of java, as that adds the Kotlin support to the classpath automatically:
> kotlin HelloKt
However, if you need to run java, then you'll need to set up the classpath yourself.
The manpage for java says:
The Java runtime searches for the startup class, and other classes used, in three sets of locations: the bootstrap class path, the installed extensions, and the user class path.
The first two are part of the Java installation, and rarely touched, so it's the user class path that you need to look at.
You need it to contain both kotlin-runner.jar and the path for your HelloKt.class file. The latter could simply be . for the current directory; the former will depend where you've installed Kotlin. (For example, I installed it using Homebrew, and that jar is currently /usr/local/Cellar/kotlin/1.3.31/libexec/lib/kotlin-runner.jar.)
The manpage continues:
-classpath classpath
-cp classpath
Specifies a list of directories, JAR archives, and ZIP archives
to search for class files. Class path entries are separated by
colons (:). Specifying -classpath or -cp overrides any setting
of the CLASSPATH environment variable.
If -classpath and -cp are not used and CLASSPATH is not set, the
user class path consists of the current directory (.).
So there are two ways you can do this: either set the $CLASSPATH environment variable before running java:
> export CLASSPATH="/usr/local/Cellar/kotlin/1.3.31/libexec/lib/kotlin-runner.jar:."
> java HelloKt
Or pass a -classpath or -cp flag:
> java -cp /usr/local/Cellar/kotlin/1.3.31/libexec/lib/kotlin-runner.jar:. HelloKt
(Or, as you say, you could build a jar file which includes the Kotlin support classes as well as your own. That's probably the best option if you're going to distribute it to machines which might not have Kotlin installed. But it's not the only option.)
As stated by #gidds, yes it is about the classpath.
The command java HelloKt is telling java the class to run is HelloKt, which is the class Kotlin uses to provide a containing class for an app called Hello, but that command does not identify where the code is that should be run. The code must be specified by the classpath. With the HelloKt.class file in the current directory, then '.' as a classpath with allow the HelloKt class to be found and the code to start, but it will quickly die because the repository 'kotlin-stdlib-1.3.11' as specified in the gradle build, must also be available to supply classes for run time. so
java -cp ".";"<path to stdlib>\kotlin-stdlib-1.3.11.jar"
will successfully run the file. Note, each jar must be a entry in the classpath, just having the folder containing the jar is not enough. On windows ';' separates entries, on mac or linux, use ':'. Each entry can be in quotes, and will need to be only if there are special characters in the path.
I can run elki's algorithm with command like this:
java -jar elki-bundle-0.7.1.jar
But how to run algorithms within elki-tutorial-0.7.0.jar?
Add all jars you want to the classpath:
java -cp elki-bundle-0.7.1.jar:elki-tutorial-0.7.0.jar de.lmu.ifi.dbs.elki.application.ELKILauncher
If you have all jars in a folder jars, then
java -cp "jars/*" de.lmu.ifi.dbs.elki.application.ELKILauncher
If you use -cp, you need to give the main class with full class name. With -jar (which only supports a single jar), the class name is in the jar.
You need to add it to your Java classpath.
I have created an executable jar file that contains two main classes. All libraries are included in the jar and the main Main-Class works fine when executing like this:
java -jar MyApplication.jar
But when I try to run the other main class like this:
java -cp MyApplication.jar my.other.mainClass
It does not include the classpath of the manifest.mf and it can not find the libraries that are in the jar file.
Is there a simple way so that the other main class can use the classpath from the manifest.mf? or should I create two separate executable jars?
You could write a class that invokes the main method of whatever class is passed as its first argument using Reflection - and configure this as the Main-class in your jar. This way you can invoke multiple main methods from the same jar with java -jar file.jar my.other.mainClass
Is there a simple way so that the other main class can use the classpath from the manifest.mf? or should I create two separate executable jars?
The JAR manifest classpath is only used if you use -jar option, and conversely the command line argument is only interpreted as a classname if -jar is NOT used. You cannot mix the two approaches.
However, this doesn't mean you have to create a second JAR file. For instance, you could write a simple shell script to launch the JVM using the classpath copied from the manifest and the secondary entry point classname.
Are you sure your problem is with libraries within the jar? What version of java are you using?
I suggest you try the following:
java -cp MyApplication.jar <add external libraries here> my.other.mainClass
So you only need to add paths to classes that are not already in the jar. You can use wild cards to shorten the list.
Here is another interesting option, Enable your unrunnable JARs to run with the java -jar command. It describes how to select a main class in the jar file and make another runnable copy.
The question says it all, I am trying to use an external library in my code, but it tells me that the packages I referenced to don't exist so I'm guessing the imports don't work. How do I do this?
Use the -cp option as described in the javac notes.
Specify where to find user class files, and (optionally) annotation processors and source files. This class path overrides the user class path in the CLASSPATH environment variable. If neither CLASSPATH, -cp nor -classpath is specified, the user class path consists of the current directory. ..
use --classpath both while compiling and running. If you use eclipse you can just
go to properties->Java buildpath->add external jars. And you are done.
Pretty basic problem here. So I have a Java package that I have created that has three classes (one has the main method). I am trying to use a few Apache Jars, and have added these to my build path in Eclipse. However Eclipse wont let me build and run it properly, so I am trying the command line. I have added the env var CLASSPATH and pointed it to my lib directory which hold the Apache Jars. However, when I try to use javac I get a bunch of errors:
package org.apache.xmlrpc does not exist
import org.apache.xmlrpc.client.XmlRpcClient;
I was reading the man page for javac and it said that:
If neither CLASSPATH, -cp nor -classpath is specified, the user class path consists of the current directory.
So I tried copying the Jars to the same location as my three source files, but no change.
Can someone please tell me what I'm doing wrong?
Thanks.
Classpath variable (or command line option of javac) must contain all jars explicitly. It cannot go through jar files stored in specified directory.
You can compile this by specifying the option -cp on the command line:
javac -cp foo.jar:bar.jar foo/bar/Baz.java
You then run it with the same option:
java -cp foo.jar:bar.jar foo.bar.Baz
It sounds like you've just set the classpath to the directory containing the jar files. You need to set it to the individual jar files, or use java.ext.dirs to set an "extension" directory containing jar files. I'd recommend using the specific jar files. Something like:
// Assuming Windows...
CLASSPATH = c:\libs\foo.jar;c:\libs\bar.jar
I'd also personally recommend specifying the classpath on the command line instead of using an environment variable - the latter will work, but it ends up being a bit more fiddly if you want to compile different projects against different libraries.
However, I'd actually recommend getting Eclipse working first, rather than retreating to the command line. It should be fine - if you could give us more information about what's failing in Eclipse, we may be able to help you with that instead.
The jar files in the current directory are not automatically included; that only refers to .class files in normal package/directory hierarchy. Jar files must be added either explicitly, or via a wildcard like javac -cp ./* (Assuming JDK6+)
(Some OSes may require an escape of the * to avoid globbing; OSX does not.)
I agree with previous answers, but I would also recommend to use proper java build tool - like ant (perceived easier to use, but not necessary) or maven ( perceived more difficult to use, but really worth learning )