We have started using our new in-house built authorization library from this version. It internally loads a native file .so and then does whatever it has to (Before it used to do based on regex).
Now in our application, we have 2 different war files that are deployed on the same tomcat in production. Both of them use this authorization library and hence both of those class loaders try loading the native file twice. Which of-course the jvm does not allow as you can only load it once.
java.lang.UnsatisfiedLinkError: Native Library /usr/lib64/xxxx-0.1.0.so already loaded in another classloader
at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1903)
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1855)
at java.lang.Runtime.loadLibrary0(Runtime.java:870)
at java.lang.System.loadLibrary(System.java:1122)
....
One solution to this problem is that, we put this authorization jar in the tomcat/lib. So that because the tomcat common class loader loads it, they are automatically available to child class-loaders (so the war files) and everyone can access it. But this solution needs special maintenance. And I dont like this tweaking. I might as well do some config if possible in my maven pom.
Is there any other simpler solution to this kind of problem? Its a pure spring application, maven based.
Related
I have a Java Web application running in Tomcat8.
I stored the native libraries in /bin folder of Tomcat installation.
I load libraries with JNA using
Native.loadLibrary("myLib",MyLib.class);
This works without any problem, if I have to update or reload the application it works.
My problem is a third-party library with its own native library.
I stored it in the same /bin directory and it works, but when I reload the application Tomcat fails to load with this error:
java.lang.UnsatisfiedLinkError: Native Library ...already loaded in another classloader
If I restart tomcat service it works again. I found this problem only during the application reload.
Decompiling the third-party library I found that its native library is loaded with this command:
System.loadLibrary("thirdpartylib");
How can I force this library load at tomcat level without a UnsatisfiedLinkError in case of application reload?
This may not actually be an answer, but it is too long for a comment.
Have you read about Tomcat classloader problems? That seems to precisely match your issue.
If that doesn't solve it... what you don't know (or don't say) is what other ClassLoader has already loaded the native library. Is this a setting in Tomcat modules, and if so can you disable that?
Since the third party wants to load its own native library, this is going to be hard to work around. If you look at the source for System.loadLibrary():
public static void loadLibrary(String libname) {
Runtime.getRuntime().loadLibrary0(Reflection.getCallerClass(), libname);
}
You can see that it is going to use the ClassLoader of the calling class, which in this case is the class of the third-party library. So to solve this you need to align the ClassLoader of the third-party lib with the ClassLoader of what tries to load the native library first. You could try enabling class loading trace and look for when that third-party class is loaded, and back up from there to find the ClassLoader.
Try to change your myLib to another name, e.g. myLib_2, to avoid conflicts.
If it is the same shared library, try below approach:
To make the "right" class loader load the native library you could create a tiny class with a single static method doing only the loadLibrary. Put this class in an extra jar and put this jar in the shared Tomcat directory. Then in the web applications replace the call to System.loadLibrary with a call to your new static method. This way the class loaders for the OpenCV classes and their native library will match and the native methods can be initialized.
See: https://stackoverflow.com/a/37213179/8034839
I developer a web application using Java. When I deploy it to my application server (Jetty, Tomcat, JBoss, GlassFish, etc.) throws an error. I can see this error message in the stacktrace:
java.lang.ClassNotFoundException
Or
java.lang.NoClassDefFoundError
What does this mean and how can I fix it?
What does this mean?
First, let's see the meaning of java.lang.ClassNotFoundException:
Thrown when an application tries to load in a class through its string name using:
The forName method in class Class.
The findSystemClass method in class ClassLoader.
The loadClass method in class ClassLoader.
but no definition for the class with the specified name could be found.
Usually, this happens when trying to open a connection manually in this form:
String jdbcDriver = "...'; //name of your driver
Class.forName(jdbcDriver);
Or when you refer to a class that belongs to an external library and strangely this class cannot be loaded when the application server tries to deploy the application.
Let's see the meaning of java.lang.NoClassDefFoundError (emphasis mine):
Thrown if the Java Virtual Machine or a ClassLoader instance tries to load in the definition of a class (as part of a normal method call or as part of creating a new instance using the new expression) and no definition of the class could be found.
The searched-for class definition existed when the currently executing class was compiled, but the definition can no longer be found.
The last part says it all: the class existed at compile time i.e. when I compiled the application through my IDE, but it is not available at runtime i.e. when the application is deployed.
how can I fix it?
In Java web applications, all third party libraries used by your application must go in WEB-INF/lib folder. Make sure that all the necessary libraries (jars) are placed there. You can check this easily:
- <webapp folder>
- WEB-INF
- lib
+ jar1
+ jar2
+ ...
- META-INF
- <rest of your folders>
This problem usually arises for JDBC connectivity jars (MySQL, Derby, MSSQL, Oracle, etc.) or web MVC frameworks libraries like JSF or Spring MVC.
Take into account that some third party libraries rely on other third party libraries, so you have to add all of them in WEB-INF/lib in order to make the application work. A good example of this is RichFaces 4 libraries, where you have to download and add the external libraries manually.
Note for Maven users: you should not experience these problems unless you have set the libraries as provided, test or system. If set to provided, you're responsible to add the libraries somewhere in the classpath. You can find more info about the dependency scopes here: Introduction to the Dependency Mechanism
In case the library must be shared among several applications that will be deployed on your application server e.g. MySQL connector for two applications, there's another alternative. Instead of deploying two war files each with their own MySQL connector library, place this library in the common library folder of the server application, this will enable the library to be in the classpath of all the deployed applications.
This folder vary from application server.
Tomcat 7/8: <tomcat_home>/lib
JBoss 7/Wildfly: <jboss_home>/standalone/lib
The class must exist under WEB-INF/classes or be inside a .jar file under WEB-INF/lib. Make sure it does.
Same problem happen with me.
Might be possible one of your libraries are using some classes internal which is not available
in your lib or maven dependency pom.xml.
Thats means you have analyze your error logs and identify these classes and then import all dependencies in maven or lib folder.
I have fixed this error by the same way.
because some of my libraries are using activation.jar and json.jar internally.
I developer a web application using Java. When I deploy it to my application server (Jetty, Tomcat, JBoss, GlassFish, etc.) throws an error. I can see this error message in the stacktrace:
java.lang.ClassNotFoundException
Or
java.lang.NoClassDefFoundError
What does this mean and how can I fix it?
What does this mean?
First, let's see the meaning of java.lang.ClassNotFoundException:
Thrown when an application tries to load in a class through its string name using:
The forName method in class Class.
The findSystemClass method in class ClassLoader.
The loadClass method in class ClassLoader.
but no definition for the class with the specified name could be found.
Usually, this happens when trying to open a connection manually in this form:
String jdbcDriver = "...'; //name of your driver
Class.forName(jdbcDriver);
Or when you refer to a class that belongs to an external library and strangely this class cannot be loaded when the application server tries to deploy the application.
Let's see the meaning of java.lang.NoClassDefFoundError (emphasis mine):
Thrown if the Java Virtual Machine or a ClassLoader instance tries to load in the definition of a class (as part of a normal method call or as part of creating a new instance using the new expression) and no definition of the class could be found.
The searched-for class definition existed when the currently executing class was compiled, but the definition can no longer be found.
The last part says it all: the class existed at compile time i.e. when I compiled the application through my IDE, but it is not available at runtime i.e. when the application is deployed.
how can I fix it?
In Java web applications, all third party libraries used by your application must go in WEB-INF/lib folder. Make sure that all the necessary libraries (jars) are placed there. You can check this easily:
- <webapp folder>
- WEB-INF
- lib
+ jar1
+ jar2
+ ...
- META-INF
- <rest of your folders>
This problem usually arises for JDBC connectivity jars (MySQL, Derby, MSSQL, Oracle, etc.) or web MVC frameworks libraries like JSF or Spring MVC.
Take into account that some third party libraries rely on other third party libraries, so you have to add all of them in WEB-INF/lib in order to make the application work. A good example of this is RichFaces 4 libraries, where you have to download and add the external libraries manually.
Note for Maven users: you should not experience these problems unless you have set the libraries as provided, test or system. If set to provided, you're responsible to add the libraries somewhere in the classpath. You can find more info about the dependency scopes here: Introduction to the Dependency Mechanism
In case the library must be shared among several applications that will be deployed on your application server e.g. MySQL connector for two applications, there's another alternative. Instead of deploying two war files each with their own MySQL connector library, place this library in the common library folder of the server application, this will enable the library to be in the classpath of all the deployed applications.
This folder vary from application server.
Tomcat 7/8: <tomcat_home>/lib
JBoss 7/Wildfly: <jboss_home>/standalone/lib
The class must exist under WEB-INF/classes or be inside a .jar file under WEB-INF/lib. Make sure it does.
Same problem happen with me.
Might be possible one of your libraries are using some classes internal which is not available
in your lib or maven dependency pom.xml.
Thats means you have analyze your error logs and identify these classes and then import all dependencies in maven or lib folder.
I have fixed this error by the same way.
because some of my libraries are using activation.jar and json.jar internally.
I have made a Java Applet that depends on some third party libriaries as well as a DLL that is called via JNI. These will obviously not be installed on clients computers. Is there anyway to package these third party libriaries and external DLLs within my Applet's JAR so that it can be run by any client with a base Java install?
Using JNI within a web application is a recipe for heartburn, particularly in Windows.
You obviously can't deploy the DLL within your WAR file and will probably require a separate installer be run by the deployer beforehand.
You'll have to ensure that your java.library.path is setup correctly, which is usually done by settings in the application server rather than something deployable in the WAR file.
The way that JNI links the native class with the library will cause class loader headaches if you try to run more than one instance of that web application. One way to work around this is to move the containing JAR file into a shared class loader (like Tomcat's common folder) but that has its own complications.
Is there anyway to package these third
party libriaries
In Eclipse, under the Java project properties (right click), I can do a:
Export... => Export as Runnable JAR
Then I tell it to pack my jar dependencies into that exported JAR.
The exported JAR will have all its dependencies packed into it.
alt text http://www.ubuntu-pics.de/bild/97131/selection_016_mg6IDm.png
I am no expert on the topic, but there are working solutions to all these problems. They might give you a headache, but some things can only be done this ways (and I am quite sure that your problem with the Entrust CSP is one of those).
You can take a look at OpenSign from the OpenOCES-project. The magic happens in org.openoces.opensign.client.applet.bootstrap.
I also believe that JNLPAppletLauncher solves the same problem, but I have no experience with i.
In our application(applet) I want to enable export functionality if one of the required jars is found. I do not want to add this jar applet references to avoid download size.
I am using Class.forName with one of the classed to check whether particular is available. In local machine Class.forName call retruns an instance although the jar is not in any of the class paths.
Can anybody explain tomcat class discovery mechanism.
Applets run at the client side(inside the browser of the user) not on the Tomcat web server, so this is unrelated to Tomcat.
You'd want to investigate how Applet classloaders work.
Usually they will try to downloading the classes from the web server under the same Url as the applet was fetched from. So if the applet is at http://www.example.com/Hello/HelloApplet
and needs the class foo.bar.MyClass it will try to download http://www.example.com/Hello/foo/bar/MyClass.class if it isn't found locally.
Based on your description of having an Applet I don't see any option but to include the jar file in the applet tag as the applet runs on the client side.
You could set HTTP cache headers for the jar files to allow the client browser to cache them, therefore, you only pay the download cost only once.
For frequently changing jar files include the a version number in the jar file name to avoid client side caching issues with same named but contentually different jars.
Edit: Although the question is about the way tomcat discovers the jars I think the root cause of the problem is elsewhere.
In Tomcat 6 on the server side Tomcat searches the $TOMCAT_HOME/lib and WEB-INF/lib directories for your jar files. If you add or remove files there you usually need to restart the entire Tomcat instance.
Edit2:
Your experience about locating the jar file might be because you run the HTML page from the same directory where your webapp resides or you have the JAR file in a common place or common classpath location (for example in the JRE/lib/ext directory).
I am having a hard time following your question. Are you trying to download classes into an applet if a particular runtime condition is met? From 6u10 I believe you could dynamically download extensions with DownloadService. Going back to 1.2, you can use URLCLassLoader.newInstance, although that wont be so good on the cache side of things.
This question isn't very clear. Tomcat and Applets are completely different in terms of class loading. Applets have a security manager that prevents certain things, such as loading arbitrary classes. They have to download the classes from the web server. The web server doesn't have to be tomcat or even Java; the applet files are just files served over plain HTTP.
As for Tomcat, this article explains version 6's classloading. In particular, Tomcat uses a heirarchy of classloaders to find classes. There are several well-known locations where jars are automatically loaded, such as $CATALINA_HOME/lib or $CATALINA_HOME/shared/lib. It also loads the web-app's own jars and classes. The classloaders work as follows:
The bootstrap class loader looks in the core Java classes folders.
The system class loader looks in the $CATALINA_HOME/bin/bootstrap.jar and
$CATALINA_HOME/bin/tomcat-juli.jar
The WebAppX class loader looks in WEB-INF/classes and then WEB-INF/lib
The common class loader looks in $CATALINA_HOME/lib folder.
The shared class loader looks in $CATALINA_HOME/shared/classes and $CATALINA_HOME/shared/lib if the shared.loader property is set in conf/catalina.properties file.
Reason: One of the other libraries(jars) referenced earlier had the class I was looking for.