I'd like sbt to generate two packages:
A WAR file, for the web app
A JAR file, which has command line and batch code
The two packages share a lot of similar code (the business logic) and dependencies, but of course the Servlet aspects are only in the WAR, and the command line and batch only in the JAR.
I'd like the JAR to run by itself, no external dependencies required (ala sbt-assembly).
How can I do this?
WAR file
You can make a war file using earldouglas/xsbt-web-plugin and use sbt-assembly for fat JAR. You might have to get a bit creative to include some files in one but exclude from the other.
Generating JAR and WAR from the same code base
If the resulting packages contain different library dependencies at the end, for example including Jetty or Netty for standalone JAR, I think it needs to be a separate subproject. See Multi Project builds.
Related
I have a multi-project SBT build: some projects are dependent on each other, some are dependent on third-party JARs, and there's a "main" project which depends on everything .
When I sbt package it, I get one JAR in each target/ directory.
What I want to achieve is getting all relevant JARs (mine and external) is one directory. Very similar to the way you package a WAR with Maven.
(And to clarify - I'm not interested in an assembled "FAT JAR" that contains all the dependencies in a single file. Just one directory with all JARs in it)
Im not 100% sure about the suprobject dependencies but I think SBT native packager should help you do something like that, and will also provide a start-script for windows and unixes:
http://www.scala-sbt.org/sbt-native-packager/GettingStartedApplications/MyFirstProject.html
I would recommend sbt-pack for creating self-contained JARs:
https://github.com/xerial/sbt-pack
I use it and haven't seen a glitch so far.
It also generates both OS X/Linux as well as Windows .bat entry scripts for the main classes/objects you choose.
I have an Eclipse project running on Tomcat, with my dependency jars sitting in the WEB-INF/lib directory. Everything is great. But the war file created on export is huge, and I'm going to need to send it back and forth to the test server, which will be time consuming. It seems like a waste.
So I put all my dependency jars in a folder, dependency_jars, in my file system, and configured the build to point there. The build works, but when I run it (still on my local machine) the app is throwing runtime errors.
Reading around, I went to the project properties and added the jars to the Web Deployment Assembly. Now the runtime works, but the exported war once again has all the jars packaged with it.
So how do I have my dependencies available for the runtime environment, without having Eclipse package them inside the war?
OK I'm not sure this is the most elegant solution but what I did is configure Tomcat to use an external library, put the dependency jars there, and then let eclipse create the war with everything in it, explode it from the command line, remove the dependency jars, repackage the war, and finally send it out.
Well, definitely not an elegant solution. But it works. Here are the steps:
Configure Tomcat to use an external resources library. Go to tomcat_home/conf/catalina.properties and add your directory under the comment that starts with "List of comma-separated paths defining the contents of the "common" classloader..."
Export war through Eclipse.
Explode the war (pun probably merited here:) jar -xvf MyWar.war
Remove your dependency jars (which are now in the external directory from step 1 above.)
Repackage the war: jar cvf MyWar.war WEB-INF
So I will be using Java Web Start to deploy the java application. When exporting to a Runnable Jar, there are three options in eclipse Helios.
Extract required libraries into JAR
Package required libraries into JAR
Copy required libraries into sub folder next to JAR.
What are differences, and how will they affect my .jnlp file?
If it's a single jar, isn't it easier because I wouldn't have to write all the different paths to all the libraries it uses?
If there are changes in both the library and the application, a single jar would be a better solution? Or would I need <jar href=''> for each individual libraries?
Also note that I need to make use of native libraries like .dll and .so files.
Extract required libraries into JAR - Extracts the actual .class files from the libraries your app uses and puts those .class files inside the runnable JAR. So, the runnable JAR will not only contain the .class files of your application, but also the .class files of all the libraries your application uses.
Package required libraries into JAR - Puts the actual JAR files of the libraries into your runnable JAR. Normally, a JAR file within a JAR file cannot be loaded by the JVM. But Eclipse adds special classes to the runnable JAR to make this possible.
Copy required libraries into sub folder next to JAR - Keeps the library JARs completely separate from the runnable JAR, so the runnable JAR will only contain the .class files of your application.
Option #2 is convenient because it packages everything neatly into a single JAR, and keeps the library JARs separated from your application's .class files.
However, a downside to packaging everything inside of a single JAR (options #1 and #2) is that, if you update your application, then the user will have to download more data to update the application. If the JARs are kept separate, then the user would only have to download the JAR that contains your application code, instead of a single, massive JAR that contains your application code and all the library code.
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