Is it possible to override the libs folder in helidon project? I want to copy jars to classpath at runtime. I was able to use -Dweblogic.ext.dirs to do that in weblogic server.
Helidon isn't an application server, so it just works with the regular Java classpath. As with any Java program, once the classpath is set, it's set. Helidon does not use multiple classloaders, so there's no runtime deploying or anything like that. (You are, of course, free to create your own classloaders or whatever you want since it's just Java.)
So: set up your classpath the way you want, and start your Java program that uses Helidon libraries.
Related
Hullo - issue is this:
I wrote a servlet in Eclipse which requires mysql-connector-java-5.1.22-bin.jar
To compile I need to add the jar via the project's "Java Build Path"
To deploy I need to add the jar to the project's "Deployment Assembly"
To run the servlet within eclipse I need to add the jar to the servlet's Run Configuration -> Classpath
It's not the end of the world re-re-repeating myself like this, but it does seem odd.
Given that Eclipse gets a lot of other stuff correct I'm guessing / hoping that maybe I'm overlooking some feature to avoid this silliness (I cannot imagine a scenario where you'd benefit from entering this in 3 different spots ... but maybe I'm being uncreative here ...).
Insights appreciated :-)
The only thing you need to do is to drop the jar in WebContent/WEB-INF/lib.
You are developing a Java Web project, so the traditional place to put the required libs (JAR files etc) is under /WEB-INF/lib. And you do it only once.
In Eclipse, when you create Dynamic Web Project the appropriate project structure is generated for you (this is a development structure). In this case you place your JAR files in ProjectName/WebContent/WEB-INF/lib folder. And this folder is *automatically included in the project's build path.
Considering the fact that it is a Java Web project (you said you use servlets) you have to deploy your web app to some Application Server, like GlassFish, JBoss, WebLogic, WebSphere etc, or more simple Web Container like Apache Tomcat. If you do this thru Eclipse, then again your web project is automatically deployed.
NB!
There may be some additional details related to using libraries.
For instance, when it comes to using database drivers (MySql, PostgreSQL, Oracle etc) Tomcat advises the following while configuring JNDI Datasource (quote):
Before you proceed, don't forget to copy the JDBC Driver's jar into
$CATALINA_HOME/lib
In your case (MySQL) see the example here: MySQL DBCP Example
Also see my answer related to Webapp configuration file organization convention.
Hope this will help you.
P.S. Here is a step-by-step example: How do I access MySQL from a web application?
So I'm relatively new to Java EE and I am having a tough time understanding when, where and why Java deployment files are packaged with their dependencies.
Say I build my project into myapp.jar, and it depends on fizz.jar, buzz.jar and JODA (joda-time-2.0.jar).
I've heard that the default classloader doesn't package jars inside of other jars, so I have to assume that if I called a jar task from Ant, then the default classloader would get invoked and myapp.jar would be created without those 3 dependencies in it.
Is this because the mentality is to deploy main-less jars in containers or other systems that will provide its requirements at runtime? If not, then how does myapp.jar ever run correctly?
What about executable jars? To met, these must be different than main-less jars, because they are meant to be standalone units, right? That means they would need all of their dependencies packaged with them, right?
Last but not least, what about jars that depend on jars that depend on jars...etc. (i.e., dependencygraphs that are huge)?
I guess all of these questions can be summed up as follows:
Is the idea behind a non-executable jar that it will be ran in such a way that it will know what classpath(s) to look on for its dependencies at runtime? (And thus doesn't need to be packaged with its dependencies)?
Is the idea behind an executable jar that it is a standalone unit and should be pacakged with its dependencies?
If my assertion to Question #1 above is correct, how does such classpath configuration take place? Are these settings that are stored inside the jar (such as in the manifest)? Else, how would a JRE know where to search for a particular jars dependencies at runtime?
Answers to these questions will actually clarify quite a lot of hangups I have with Java fundamentals, and so any input/help here will be appreciated enormously! Thanks
Jars do not know about other jars (unless assisted by some tools like Maven). The inter dependency of the jars is purely resolved by the Classloaders. I strongly recommend to have some idea about classloaders.
To address your questions,
Is the idea behind a non-executable jar that it will be ran in such a way that it will know what classpath(s) to look on for its dependencies at runtime? (And thus doesn't need to be packaged with its dependencies)?
NO. As mentioned, it's the classloader which looks the classpath and the jars mentioned therein. The jars do not have any information about other jars.
Is the idea behind an executable jar that it is a standalone unit and should be packaged with its dependencies?
NO. A classloader loads the standalone executable jars at the start of execution. If it needs other dependency jars it'll look into the classpath for those jars.
If my assertion to Question #1 above is correct, how does such classpath configuration take place? Are these settings that are stored inside the jar (such as in the manifest)? Else, how would a JRE know where to search for a particular jars dependencies at runtime?
For standalone jar (executable jar), the classloader looks for the classpath variable OR classpath passed while invoking the application.
For other type of application (WAR, EAR), There are predefined places/folders where the dependencies should be placed in order to get picked up. This is standardized by specs.
In a nutshell, it's the classloader which is pulling all the threads. There is standard places where it looks for all the dependent jars. This link nicely describes how the classloaders in standalone application and in a deployed (in some container) works.
JAR files are a way to package togher complex java application. Jar application are easy to move between diffrent machines and operating system.
I think the right way to use Jars is not tu put everything (every dependencies) into a single jar.
For example if your application uses a jar libryra (for example jdbc) to access a database you should not put the jdbc jar into your jar.
You had better to build a jar file with only your .class file.
Of course your code needs the jdbc jar to work properly. Here comes to explain how the virtual machine searches for extarnal classes:
-it first searches in the directories that contain the classes that come standard with J2SE (the path depends on your installation)
-it searches in the directories specified by the classpath (a classpath is either an environment variable or an option of the java command)
for example:
java -jar -c /your/path/ yourApp.jar
will run your application and will search th classes your application refers to in the directory /your/path/ so if you have external jars you can put them in that directory.
For detailed documentation: http://download.oracle.com/javase/tutorial/deployment/jar/index.html
How should I add JAR libraries to a WAR project in Eclipse without facing java.lang.ClassNotFoundException or java.lang.NoClassDefFoundError?
The CLASSPATH environment variable does not seem to work. In some cases we add JAR files to the Build Path property of Eclipse project to make the code compile. We sometimes need to put JAR files inside /WEB-INF/lib folder of the Java EE web application to make the code to run on classes inside that JAR.
I do not exactly understand why CLASSPATH does not work and in which cases we should add JARs to Build Path and when exactly those JARs should be placed in /WEB-INF/lib.
The CLASSPATH environment variable is only used by the java.exe command and even then only when the command is invoked without any of the -cp, -classpath, -jar arguments. The CLASSPATH environment variable is ignored by IDEs like Eclipse, Netbeans and IDEA. See also java.lang.ClassNotFoundException in spite of using CLASSPATH environment variable.
The Build Path is only for libraries which are required to get the project's code to compile. Manually placing JAR in /WEB-INF/lib, or setting the Deployment Assembly, or letting an external build system like Maven place the <dependency> as JAR in /WEB-INF/lib of produced WAR during the build, is only for libraries which are required to get the code to deploy and run on the target environment too. Do note that you're not supposed to create subfolders in /WEB-INF/lib. The JARs have to be placed in the root.
Some libraries are already provided by the target JEE server or servletcontainer, such as JSP, Servlet, EL, etc. So you do not need put JARs of those libraries in /WEB-INF/lib. Moreover, it would only cause classloading trouble. It's sufficient to (indirectly) specify them in Build Path only. In Eclipse, you normally do that by setting the Targeted Runtime accordingly. It will automatically end up in Build Path. You do not need to manually add them to Build Path. See also How do I import the javax.servlet / jakarta.servlet API in my Eclipse project?
Other libraries, usually 3rd party ones like Apache Commons, JDBC drivers and JEE libraries which are not provided by the target servletcontainer (e.g. Tomcat doesn't support many JEE libraries out the box such as JSF, JSTL, CDI, JPA, EJB, etc), need to end up in /WEB-INF/lib. You can just copy and paste the physical JAR files in there. You do not necessarily need to specify it in Build Path. Only perhaps when you already have it as User Library, but you should then use Deployment assembly setting for this instead. See also ClassNotFoundException when using User Libraries in Eclipse build path.
In case you're using Maven, then you need to make absolutely sure that you mark libraries as <scope>provided</scope> if those are already provided by the target runtime, such as JEE, Servlet, EL, etc in case you deploy to WildFly, TomEE, etc. This way they won't end up in /WEB-INF/lib of produced WAR (and potentially cause conflicts with server-bundled libraries), but they will end up in Eclipse's Build Path (and get the project's code to compile). See also How to properly install and configure JSF libraries via Maven?
Those JARs in the build path are referenced for the build (compile) process only. If you export your Web Application they are not included in the final WAR (give it a try).
If you need the JARs at runtime you must place them in WEB-INF/lib or the server classpath. Placing your JARs in the server classpath does only make sense if several WARs share a common code base and have the need to access shared objects (e.g. a Singleton).
If you are using Maven:
Open the project properties, and under Deployment Assembly click Add...
Then select Java Build Path Entries and select Maven Dependencies
Resolved by setting permissions.
Had related issue using PySpark and Oracle jdbc. The error does not state that the file cannot be accessed, just that the class cannot be loaded.
So if anyone still struggles, check the permissions. Some might find it obvious tho'.
I want to give the answer for the folowing link question ClassNotFoundException oracle.jdbc.driver.OracleDriver only in servlet, using Eclipse
Ans: In Myeclipse go to Server-->left click on Myeclipse Tomcat7-->Configure Server Connector-->(Expand)Myeclipse Tomcat7--> Paths-->Prepend to classpath-->Add jar (add oracle14 jar)-->ok
What is the simplest way to package a Scala application for use on a desktop PC? I'm guessing that would be in the form of a jar file.
At the moment I'm using SBT to compile and run programs
I'd be interested in solutions for machines that have Scala installed (and the library in their classpath), as well as those that only have Java.
The simplest (and the most consistent) way to package a Scala application, is packaging into a JAR (like you do with normal Java applications). As long as JAR consists of standard compiled Java classes, you may run "Scala" JAR, even if you don't have Scala runtime at the box (all you need is a Java Runtime and scala-lang.jar on the classpath). You may specify the main class (gateway to functionalities of your application) in the manifast
Main-Class: mypackage.MyClass
so that you'll be able to call it only passing a JAR name to java.exe.
java -jar myjar.jar
You may specify the main class in SBT project definition.
http://www.scala-sbt.org/sbt-native-packager/index.html
The plugin allows you to package in a variety of formats(zip, tar, deb, dmg, msi, etc) and in different archtypes.
I need to connect to a MongoDB instance from my EJB3 application, running on glassfish 3.0.1. The Mongo project provides a set of drivers, and I'm able to use them in a standalone Java application.
How would I use them in a Java EE application? Or maybe better phrasing: how would I make a 3rd party library available to my application when it runs in an EJB container?
At the moment, I'm getting a java.lang.NoClassDefFoundError when deploying a bean that
tries to import from the library:
[#|2010-03-24T11:42:15.164+0100|SEVERE|glassfishv3.0|global|_ThreadID=28;_ThreadName=Thread-1;|Class [ com/mongodb/DBObject ] not found. Error while loading [ class mvs.core.LocationCacheService ]|#]
[#|2010-03-24T11:42:15.164+0100|WARNING|glassfishv3.0|javax.enterprise.system.tools.deployment.org.glassfish.deployment.common|_ThreadID=28;_ThreadName=Thread-1;|Error in annotation processing: java.lang.NoClassDefFoundError: com/mongodb/DBObject|#]
[#|2010-03-24T11:42:15.259+0100|SEVERE|glassfishv3.0|javax.enterprise.system.core.com.sun.enterprise.v3.server|_ThreadID=28;_ThreadName=Thread-1;|Exception while loading the app
org.glassfish.deployment.common.DeploymentException: java.lang.NoClassDefFoundError: com/mongodb/DBObject
at org.glassfish.weld.WeldDeployer.event(WeldDeployer.java:171)
at org.glassfish.kernel.event.EventsImpl.send(EventsImpl.java:125)
at org.glassfish.internal.data.ApplicationInfo.load(ApplicationInfo.java:224)
at com.sun.enterprise.v3.server.ApplicationLifecycle.deploy(ApplicationLifecycle.java:338)
I tried adding it to the NetBeans project (Properties -> Libraries -> Compile -> Add Jar, enable 'Package'), and I also tried manually copying the jar file to $GF_HOME/glassfish/domains/domain1/lib (where the mysql-connector already resides).
Do I need to 'register' the library with the container? Reference it via Annotation? Extend the classpath of the container to include the library?
Hmm... Shouldn't you put this "driver" in glassfishv3/glassfish/domains/domain1/lib/ext?
You could put shared libs to lib/ext of your domain. commons-logging and jdbc drivers are often added in this domain path.
Common Class Loader
GlassFish v2 has a well defined Class
Loader hierarchy which identifies the
common class loader as the proper way
to deal with shared libraries. So to
make a long story short, putting you
libraries and other framework JARs in
domains/domain1/lib is all you need to
do.
lib/, not lib/ext
The person asking me the question had
tried putting the libraries in
domains/domain1/lib/ext which
triggered an interesting
ClassNotFoundError for core Java EE
classes such as
javax.servlet.http.HttpServlet. Shing
Wai Chan was quick to explain that
domains/domain1/lib/ext is part of
-Djava.ext.dirs which makes any of its JARs be considered as a JDK extension
which means web app frameworks placed
there will be loaded before
webcontainer implementation classes as
they are higher up in the classloader
delegation chain.
Glassfish has own Class loader hierarchy, http://docs.oracle.com/cd/E19798-01/821-1752/beade/index.html
I face the same problem in my project and then I put all my Third party libraries in domain/domain1/lib and my problem solved. On other way round, my problem was solved too by putting libraries in glassfish/lib.
In my case I was using Oracle Express Edition 11gR2 and Glassfish 3.1.2 and the ONLY way that works in my case was putting the ojdbc6 in:
C:\Program Files\glassfish-3.1.2.2\glassfish\lib
Go to your Glassfish doamin directory.
Then go to lib folder.
Place the libraries there.
Restart the glassfish and run.
(Ex) C:\glassfish3\glassfish\domains\domain1\lib
Try to put Your libs into $GF_HOME/glassfish/modules/.
It's dirty, but will work.