I've been trying to load the JDBC MySQL connector with the following code:
import java.sql.*;
public class dbTest{
public static void main(String[] args) throws SQLException, ClassNotFoundException
{
Class.forName("com.mysql.jdbc.Driver");
}
}
And I keep getting a class not found exception:
java.lang.ClassNotFoundException
at edu.rice.cs.plt.reflect.PathClassLoader.findClass(PathClassLoader.java:148)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at dbTest.main(dbTest.java:6)
I have added the path to the driver (mysql-connector-java-3.1.14-bin.jar) to my classpath and double checked to make sure it was correct. I also added copies of the jar to the ext folder of my Java installation based on what I read from this article: http://www.developer.com/java/data/jdbc-and-mysql-installation-and-preparation-of-mysql.html
I also searched through posts of others who have had this problem, but all of the responses so far have been saying to add the connector jar to the classpath, which I have already done.
Any help would be greatly appreciated.
I have added the path to the driver
(mysql-connector-java-3.1.14-bin.jar)
to my classpath
The exception tells you that you didn't do it correctly.
How are you setting CLASSPATH? If it's an environment variable, you're going to learn that IDEs and app servers ignore it. Don't use it.
Don't put it in the /ext directory of your Java JDK, either.
The right way to do it depends on how you're using it:
If you're running inside an IDE like Eclipse or IntelliJ, you have to add the JAR to a library.
IF you're running in a command shell, use the -p option for javac.exe when you compile and java.exe when you run.
If you're using it in a web app, you can start by putting it in the WEB-INF/lib directory of your WAR file. If you're using a servlet/JSP engine like Tomcat 6, put it in the Tomcat /lib directory.
On IntelliJ this is how I solved this problem:
File > Project Structure > Libraries > +
Locate the jdbc connector. For me it was on C:\Users\MyName.InteliJIdea13\config\jdbc-drivers
There are two classpaths in java. Build path and run path. Build path is used when compiling .java files into .class files. In a language like C you have a linker stage that fills in all the missing symbols when you run the linker on a bunch of object files. Thats why for .exe(windows) or other native binaries(linux) there is no run path. Java is slightly different because the compiled .class definitions get loaded by the jvm as they are needed.
What the net out of this is that you have to supply a runtime classpath to the jvm. At the command line you use java.exe which searches a few places by default including $CLASSPATH, the current directory/lib, and whatever you supply to the -cp option.
IDEs are different from the command line because they are attempting to shield you from some of the nastiness of running java.exe and supplying the locations where all the .class files are(which would be onerous on a large project).
Most IDE's have some sort of "Run Configuration" tab that allows you to specify certain libraries or locations with classes that will be used when you run your application. Below is how to set the run path in eclipse,netbeans, and intellij.
http://javahowto.blogspot.com/2006/06/set-classpath-in-eclipse-and-netbeans.html
http://www.jetbrains.com/idea/webhelp/run-debug-configuration-application.html
Related
I'm making a basic game in Java using the LWJGL Library via Netbeans.
I've created a library with the lwjgl, lwjgl_util, and jinput .jar's, and I added -Djava.library.path=C:\LWJGL\native\windows to the "Run" category in the project's properties.
When I run the file in Netbeans, it runs perfectly with no issue. But when I run the .jar via double-clicking the file, nothing pops up (not even the momentary cmd error window, as far as I can tell). And when I run the file via command line, I get:
C:\Users\200160765>java -jar "C:\Users\200160765\Documents\NetBeansProjects\Game
\dist\Game.jar"
Exception in thread "main" java.lang.UnsatisfiedLinkError: no lwjgl in java.libr
ary.path
at java.lang.ClassLoader.loadLibrary(Unknown Source)
at java.lang.Runtime.loadLibrary0(Unknown Source)
at java.lang.System.loadLibrary(Unknown Source)
at org.lwjgl.Sys$1.run(Sys.java:73)
at java.security.AccessController.doPrivileged(Native Method)
at org.lwjgl.Sys.doLoadLibrary(Sys.java:66)
at org.lwjgl.Sys.loadLibrary(Sys.java:82)
at org.lwjgl.Sys.<clinit>(Sys.java:99)
at org.lwjgl.opengl.Display.<clinit>(Display.java:130)
at game.Draw.createWindow(Draw.java:198)
at game.Draw.init(Draw.java:214)
at game.Draw.run(Draw.java:56)
at game.Main.main(Main.java:9)
I've tried moving the DLL's and .jar library files around to the 'lib' folder in the same directory as Game.jar, and moving them to the same directory as Game.jar, but I get the same error. Could someone help me as to why I can't seem to get this working outside of netbeans?
you have to point the jvm to where the native files are located using a command line parameter -Djava.library.path="path/to/natives". You could use a batch (.bat) file to specify this and start your application for you.
Alternatively you can use a tool like JarSplice to create a single executable jar file from all your jars and at the same time include your native files inside it. It automates the tricky part of specifying the natives manually and provides a nicer end user experience.
To use JarSplice just select your game.jar, lwjgl.jar, lwjgl_util.jar, and jinput.jar in the jars tab. Then all the *.dll, *.so, *.dylib and *.jnilib files in the natives tab. Add your main class on the class tab and create the single executable jar.
LWJGL needs the native components for your particular platform to be in java.library.path. These are in the subdirectory native in the LWJGL distribution and end in .so on Linux, OSX and Solaris and .dll for windows.
When I had this issue, it was because i accidentally put the argument to specify the location of the natives (-Djava.library.path=/native/) in the field called 'Arguments' under the run category of the options panel, instead of 'vm Options'.
As seen here: http://s30.postimg.org/6f90akidt/Capture.png
And yet another way to do this is with Java Web Start (jnlp): http://lwjgl.org/forum/index.php?topic=3763.0
This makes sharing your project easier in some ways.
I had this problem and fixed it using jarSplice (http://ninjacave.com/jarsplice)
make sure you delete all of the preplaced natives in your jar before you create the fat jar, otherwise it will create a duplicate error
I also got the same error and then realised that I named the file "my_lib.zip" instead of "my_lib.jar". Maybe it may help someone.
Another thing to check:
If you are using a 32 bit JVM, you need 32 bit libraries. (Even on a 64 bit OS)
If you are using a 64 bit JVM, you need 64 bit libraries.
I have been following this tutorial accordingly.
Up to running the FirstExample class in the command prompt is when it starts to freak out for some reason. After attempting to run the following command:
java FirstExample
I get the following exception:
Exception in thread "main" java.lang.NoClassDefFoundError: FirstExample
I understand that it can't find the FirstExample class due to the classpath (for some reason) so I executed the following command:
java -cp . FirstExample
And now it returns a new exception:
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
Now it can't find the JDBC Driver. This confuses me because for starters, I ran the exact same coding through Eclipse and it works as expected, and secondly, I went as far as to ensure that I execute the same class file that Eclipse is executing, and the command prompt still returns exceptions. I also went as far as to put the FirstExample file in a separate folder, just for the purpose of copying and pasting the MySQL Connector into the same folder, and I still get exceptions.
I just don't understand whats going on, can someone help me please?
Many thanks.
The file path to the connector is as followed:
C:\Program Files\MySQL\mysql-connector-java-3.1.14\mysql-connector-java-3.1.14-bin.jar
Hope this helps.
For testing purposes, I have placed the FirstExample class under the following path:
C:\java
This confuses me because for starters, I ran the exact same coding through Eclipse and it works as expected
This is because in Eclipse you add the libraries to the Build Path, and it will use all the libraries specified there in the classpath automatically when running your project. This can be noted here:
In order for you to execute your project using third party libraries from command line tools, you should specify the libraries manually in your classpath explicitly:
java -cp <path/to/mysql_jar/goes/here>:. FirstExample
By your comment:
the path to the MySQL file is: C:\Program Files\MySQL\mysql-connector-java-3.1.14\mysql-connector-java-3.1.14-bin.jar (...) I have placed the FirstExample class under C:\java
This should be the command line to use:
java -cp "C:\Program Files\MySQL\mysql-connector-java-3.1.14\mysql-connector-java-3.1.14-bin.jar; ." FirstExample
Note that it is better to store all the third party libraries in a single folder within your project, usually called lib, and put a reference to there. Assuming your current folder has a lib folder and all the third party libraries are copied there, the command line would be:
java -cp "lib\*; ." FirstExample
Use the next example to add your jars to the classpath:
java -cp "jdbc.jar;lib/*" my.package.FirstExample
You need to have the class com.mysql.jdbc.Driver (and all the imported classes) in the classpath too.
You should download the jar (http://dev.mysql.com/downloads/connector/j/5.0.html) and add it to the classpath.
The ClassNotFound Exception rises when there is an issue with the class name that you have written in Class.forName() or if the package is not set to the classpath variable. Make sure that you have added the jar file to the classpath ( C:............\jarfilename.jar;).
This is applicable for any JDBC Driver and jar files. The .jar files that are added to the classpath will not be visible to IDEs, in this case, you need to add the jar files to buildpath (in eclipse) or you can also copy the jar files to ext folder available in the Java installation folder.
Also note that the jar files of the DB Softwares may vary based on the DB software version that you are using for example if you are using the Oracle 11g, you need ojdbc6.jar file, in other versions of Oracle the number changes like ojdbc14.jar etc.
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
How can i make an executable of my project in Java?
I tried to right click on my project and selected export .
the problem is that the exported jar file wont open when I execute it! Have I missed something? And is there a way to make an .exe executable from my project?
when I execute the jar file in cmd it says :
Exception in thread "main" java.lang.UnsatisfiedLinkError: no lwjgl in java.libr
ary.path
at java.lang.ClassLoader.loadLibrary(Unknown Source)
at java.lang.Runtime.loadLibrary0(Unknown Source)
at java.lang.System.loadLibrary(Unknown Source)
at org.lwjgl.Sys$1.run(Sys.java:73)
at java.security.AccessController.doPrivileged(Native Method)
at org.lwjgl.Sys.doLoadLibrary(Sys.java:66)
at org.lwjgl.Sys.loadLibrary(Sys.java:95)
at org.lwjgl.Sys.<clinit>(Sys.java:112)
at org.lwjgl.opengl.Display.<clinit>(Display.java:135)
at org.newdawn.slick.AppGameContainer$1.run(AppGameContainer.java:39)
at java.security.AccessController.doPrivileged(Native Method)
at org.newdawn.slick.AppGameContainer.<clinit>(AppGameContainer.java:36)
at JavaGame.Game.main(Game.java:34)
UnsatisfiedLinkError indicates that you're missing a native library (usually a .dll file on Windows, or .so file on Linux). You'll need to do one of the following:
Not recommended: Copy the native library to a location on the default java.library.path (on Windows, this includes C:\Windows\system32)
Not recommended: Copy the native library to a directory, then run your program with java -Djava.library.path=dir/containing/library -jar <jarfile>
Recommended: Bundle the DLL in your jarfile, then modify your code to extract the DLL to a temporary directory and load it using System.load or System.loadLibrary.
You can use either of the first two solutions above as a quick hack to get it working, but neither of those solutions is very good. The best solution from a deployment standpoint is #3 above.
In your case, you're using the Lightweight Java Game Library, or lwjgl as referenced in your UnsatisfiedLinkError. So you'll need to include any DLL(s) that come with lwjgl.
When you unzip lwjgl, you'll notice that it has a native directory with a subdirectory for each supported platform. Here is a listing of lwjgl's Windows DLLs:
To implement solution #3 above and make your executable jarfile cross-platform:
in your project/jarfile, create a separate directory for each platform
put all the native libraries for each platform in the appropriate directory (it may be helpful to put them in the same directory as some utility class that you'll later use to extract them)
when you export your program to a jarfile, make sure the native libraries are included
look up the platform/operating system (e.g., System.getProperty("os.name"))
in your Java code (probably in your main method or some utility method), create a temporary directory
for whatever platform you looked up in step 3, extract the appropriate native libraries into the directory you created in step 4 (hint: use Class.getResourceAsStream to get an InputStream, then use Files.copy to extract it to a file)
for each library you extract in step 5, call System.load("path/to/library_file")
See https://stackoverflow.com/a/1611367/44737 for a nice example including code.
You can either package everything in a jar manually using the jar command line tool or you can automate the process of packaging your jar using tools like Ant, Maven or Gradle.
Once you have your class files properly packaged in jar file, you can execute them by creating a script file appropriate for your operation system. For instance a batch file in windows or a bash file in Linux.
All you have to do is invoke the java command and provide your class path and the name of your application entry point.
#!/bin/bash
java -cp myApp.jar com.my.app.Main
And that's it. You execute your application by invoking that script.
Additionally, you can make arrangements to create an executable jar, by means of defining a MANIFEST file for you jar file. In that manifest file you can place a property Main-Class that indicates your application entry point and you can define another property called Class-Path which allows you to specify a list of other jars needed by your application.
See Running Jar-Packaged Software.
If you package your jar this way, some operating systems allows you to execute the application by simply double-clicking the jar.
But most probably, you still will need to create a script, just a bit different this time:
#!/bin/bash
java -jar myApp.jar
See the Java Tutorial: Packaging Applications in Jar Files.
Ultimately, if you really, really need to create an executable file, and if you're working on windows, you may consider a tool like WinRun4j.
I am new to Java and I am not sure how apt is my question title. Please suggest any better title.
I have got a Java API which has many executable modules which do various things related to parsing MS Outlook's .pst files. And my problem is that I am getting this exception when I run the execute command to execute a .class file of one module of the API(java -classpath /opt/Java/libs/JPST/lib/jpst.jar /opt/Java/libs/JPST/examples/GetInboxMessages/bin/Example)-
Exception in thread "main" java.lang.NoClassDefFoundError: /opt/Java/libs/JPST/examples/GetInboxMessages/bin/Example
Caused by: java.lang.ClassNotFoundException: .opt.Java.libs.JPST.examples.GetInboxMessages.bin.Example
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: /opt/Java/libs/JPST/examples/GetInboxMessages/bin/Example. Program will exit.
So far ...
You can check my previous question where I concluded that I was correctly running the compile and execute commands. But I am still getting the above mentioned `exception.
I asked the API's developer who says that I should get Eclipse or Netbeans IDE. He said that the
examples folder inside the API's
folder structure is entire Eclipse
workspace.
and also said that
It is easier to compile and run all
examples.
And now ...
So, I have setup Eclipse Helios for Java. Can anyone tell me how is it easy to compile and run all the examples (I think the modules inside the examples folder) using the IDE. I have earlier worked with Eclipse for PHP but never for Java.
Folder structure of the API
I need to execute a .class file of one of those modules (many module folders are present inside examples directory). There are many such modules present inside the examples folder of the API. Each of these modules folders contain a bin folder (containing .class file) and src folder (containing .java file) . I need to execute one such .class file.
There is a lib directory containing a .jar file (which is needed to be referenced by my target .class file). The lib directory is at the same level as the examples directory.
Solution
I have verified that the solution given by Jonathan works (verified only without-using-elipse case). To make it more clear the classpath needs to include all the class locations in both compile and execute commands. So, if you need to compile and execute an Example.java file with a dependency Parent.jar do this:-
Compile
javac -classpath /path/to/Parent.jar/file/Parent.jar:/path/to/Example.java/file/ Example.java
Execute
java -classpath /path/to/Parent.jar/file/Parent.jar:/path/to/Example.class/file Example
And note the separator - should be : for linux and ; for windows.
Thanks,
Sandeepan
When Eclipse starts it should ask you which workspace to use. Select the examples folder and, if it really is an eclipse workspace, you should see all the projects already set up (it may take some time to build everything depending on the size of the projects and the speed of your machine). Then simply find the class you want and run it. If everything is set up correctly it should just work. If not you may have to go back to the developer for more details.
But I don't think you need Eclipse to run that one class. Looking at the stacktrace you provided at the beginning of your question it looks like it failed to run because you haven't set your classpath properly. Try:
java -classpath /opt/Java/libs/JPST/lib/jpst.jar:/opt/Java/libs/JPST/examples/GetInboxMessages/bin Example
To very briefly explain: The classpath lists the places where Java looks for the classes it needs. You specify the class to run relative to the classpath, not as a file path. Since the class you are trying to run in in the folder "/opt/Java/libs/JPST/examples/GetInboxMessages/bin" this folder must be on the classpath (note, I am assuming a unix based system, if you are using windows use ';' to separate entries not ':'). Then simply specify the class to run by itself relative to the classpath (which in this case is just the class name by itself).
Please be aware this is a very basic overview, things get a more complex if you start using packages (folders that would appear below the bin folder). This is one advantage of using a program like Eclipse since it will handle a lot of this for you.
Sounds like a classpath issue.
Right click on your project in eclipse.
Go to buildPath > configure build path
Make sure the jar file is referenced in the libraries tab and if it isn't add it.