Develop Reference

springboot embedded tomcat and tomcat-embed-jasper

I sometimes see these following declaration in pom.xml...
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>jstl</artifactId>
</dependency>
<dependency>
<groupId>org.apache.tomcat.embed</groupId>
<artifactId>tomcat-embed-jasper</artifactId>
<scope>provided</scope>
</dependency>
....
as you can see, spring-boot-starter-web was declared as well
as tomcat-embed-jasper.
isn't it spring-boot-starter-web already have an embedded tomcat?
why some developers still declare tomcat-embed-jasper along with boot-starter-web? or is there any reason?

As you said, the spring-boot-starter-web includes the spring-boot-starter-tomcat. You could check it here
The spring-boot-starter-tomcat includes the tomcat-embed-core. You could check it here
But, seems like tomcat-embed-core doesn't include tomcat-embed-jasper. In fact, is tomcat-embed-jasper who includes dependency with tomcat-embed-core. Check it here
Anyway, the tomcat-embed-jasper is marked as provided, so indicates that you expect the JDK or a container to provide the dependency at runtime. This scope is only available on the compilation and test classpath, and is not transitive.
In conclusion, the spring-boot-starter-web includes the tomcat embedded dependency but it doesn't includes the jasper embedded dependency, so that should be the reason to declare it separately.
Also, remember that using Spring IO Platform as parent you are able to manage dependencies easily. To know more about this you could read my post
Hope it helps,

Extended from jcgarcia's answer.
Even it is provided, but when you build as war, spring-boot-maven-plugin will include two more jar :
ecj-3.12.3.jar
tomcat-embed-jasper-8.5.23.jar

To those who are still facing this error in 2022 with Java Version 17, Maven Version 3.0.0 and Package Jar. I also ran into the same issue just now, seems like even though we set <scope>Provided</scope> Maven is not picking up the jar. What you can do instead is just take that completely off while adding the dependency and run the Maven to install dependencies again. It will fix it for sure. So your pom.xml file will go:-
From
<dependency>
<groupId>org.apache.tomcat.embed</groupId>
<artifactId>tomcat-embed-jasper</artifactId>
<scope>provided</scope>
</dependency>
To
<dependency>
<groupId>org.apache.tomcat.embed</groupId>
<artifactId>tomcat-embed-jasper</artifactId>
</dependency>

Missing plugins found while loading a transformation on Kettle

I receive this error whenever I run my extraction from the command line, not in the Spoon UI.
Missing plugins found while loading a transformation
Step : MongoDbInput
at org.pentaho.di.job.entries.trans.JobEntryTrans.getTransMeta(JobEntryTrans.java:1200)
at org.pentaho.di.job.entries.trans.JobEntryTrans.execute(JobEntryTrans.java:643)
at org.pentaho.di.job.Job.execute(Job.java:714)
at org.pentaho.di.job.Job.execute(Job.java:856)
... 4 more
Caused by: org.pentaho.di.core.exception.KettleMissingPluginsException:
Missing plugins found while loading a transformation
My maven dependencies is as follows.
<dependency>
<groupId>rhino</groupId>
<artifactId>js</artifactId>
</dependency>
<dependency>
<groupId>pentaho-kettle</groupId>
<artifactId>kettle-core</artifactId>
</dependency>
<dependency>
<groupId>pentaho-kettle</groupId>
<artifactId>kettle-engine</artifactId>
</dependency>
<dependency>
<groupId>pentaho-library</groupId>
<artifactId>libbase</artifactId>
<version>5.1.0.0-752</version>
</dependency>
<dependency>
<groupId>pentaho</groupId>
<artifactId>pentaho-big-data-plugin</artifactId>
<version>5.1.0.0-751</version>
</dependency>
<dependency>
<groupId>pentaho</groupId>
<artifactId>pentaho-mongodb-plugin</artifactId>
<version>5.1.0.0-751</version>
</dependency>
<dependency>
<groupId>org.mongodb</groupId>
<artifactId>mongo-java-driver</artifactId>
<version>2.11.1</version>
</dependency>
<dependency>
<groupId>pentaho</groupId>
<artifactId>metastore</artifactId>
<version>5.1.0.0-751</version>
</dependency>
<dependency>
<groupId>pentaho-library</groupId>
<artifactId>libformula</artifactId>
</dependency>
<dependency>
<groupId>simple-jndi</groupId>
<artifactId>simple-jndi</artifactId>
</dependency>
<dependency>
<groupId>org.drools</groupId>
<artifactId>drools-compiler</artifactId>
</dependency>
<dependency>
<groupId>org.drools</groupId>
<artifactId>drools-core</artifactId>
</dependency>
<dependency>
<groupId>org.postgresql</groupId>
<artifactId>postgresql</artifactId>
</dependency>
</dependencies>
Am I missing anything?

before init kettleEnviroment
KettleEnviroment.init();
you should add this code like
StepPluginType.getInstance().getPluginFolders().add(new PluginFolder("your plugins path", false, true));

Having the MongoDB plugin as a dependency only works for compilation. When PDI runs it looks for a plugins/ folder under the current directory, and will load all plugins from there. You can override the location by setting the KETTLE_PLUGIN_BASE_FOLDERS system property. Either way, you'll want a plugins/ folder and to unzip the MongoDB plugin package (not the JAR) into plugins/. That should put a folder called pentaho-mongodb-plugin under plugins/, and if PDI is pointing at that plugins/ folder, it should load and use the plugin successfully at runtime.

You must run Kitchen from Kettle installation directory.
As written here:
http://wiki.pentaho.com/display/EAI/Kitchen+User+Documentation
Please make sure that you are positioned in the Kettle directory
before running the samples below. If you put these scripts into a
batch file or shell script, simply do a change directory to the
installation directory

I had the same error message after an update from version 7 to 8.3. In my case, it was the step 'Abort' and 'Attend' that caused the error. In version 8 these two steps aren't part of the library "kettle-engine-8.3.0.0-371.jar" anymore, they are now part of the library "pdi-core-plugins-impl-8.3.0.0-371.jar" in a new plugin. I had to add the plugin in the maven-dependencies:
<dependency>
<groupId>org.pentaho.di.plugins</groupId>
<artifactId>pdi-core-plugins-impl</artifactId>
<version>8.3.0.0-371</version>
</dependency>
But that was still not everything, I still got the error message. The reason: "To use non-native plugins with an embedded Pentaho Server, you must configure the server to find where the plugins reside" (https://help.hitachivantara.com/Documentation/Pentaho/8.0/Developer_Center/PDI/Embed).
So above the line KettleEnvironment.init() in my java-code, I added this one:
System.setProperty("KETTLE_PLUGIN_CLASSES", "org.pentaho.di.trans.steps.abort.AbortMeta,org.pentaho.di.trans.steps.append.AppendMeta");
KettleEnvironment.init();
This way worked for me. There's also a suggestion using a plugin-folder (see the link or the other answers) and working with KETTLE_PLUGIN_BASE_FOLDER instead.
Unfortunately, the error message doesn't mention which plugin is missing. I deleted and added them (in my local Spoon application) until I found exactly the one that was missing.

Just edit spoon.sh and add
OPT="$OPT -DKETTLE_PLUGIN_BASE_FOLDERS=$BASEDIR/plugins"
right after the line where the OPT variable is set.
This is actually the solution from mattyb. Editing spoon.sh will fix the problem for good.
Another solution is to create a symbolic link in your ${KETTLE_HOME}/.kettle directory which points to the plugins folder.

Assertion Error when running `SolrTestCaseJ4` tests: Fix your classpath to have tests-framework.jar before lucene-core.jar

When trying to run simple tests using Solr's testing framework I get the following Error message:
java.lang.AssertionError: fix your classpath to have tests-framework.jar before lucene-core.jar
at __randomizedtesting.SeedInfo.seed(...)
I'm using the IntelliJ IDEA IDE. How do I fix the classpath to have tests-framework.jar before lucene-core.jar?

Even though #mindas's answer above pointed me to it, it is not in a sense, a direct answer to the question. I faced this exact issue today, and found out that the lucene-core.jar wasn't being pulled itself. I added it to my pom.xml and now I don't get the above mentioned error anymore. Here is what the <dependencies> section of my pom.xml now looks like:
<dependencies>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.5</version>
</dependency>
<dependency>
<groupId>org.apache.solr</groupId>
<artifactId>solr-test-framework</artifactId>
<version>4.6.0</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.apache.lucene</groupId>
<artifactId>lucene-core</artifactId>
<version>4.6.0</version>
<scope>test</scope>
</dependency>
</dependencies>
Note: Make sure that your lucene-core and solr-test-framework versions match.
Hope this helps someone else landing on this page.

In certain situations, the order of libraries may be important. <..>
For the compilation to succeed, certain libraries (e.g. the ones having to do with the JDK itself and its extensions) must be included in the module bootclasspath. So, such libraries must appear in the list before the JDK.
For more details see relevant chapter of IntelliJ Web help.

Maven error when resolving dependency

I am new to Maven and am trying to set up one of my first POMs. My application will cache using EhCache. Going to Maven Central Repo (link here) I copy-n-pasted the <dependency> tag and copy it into my pom.xml like so:
...many dependencies above this point
<dependency>
<scope>compile</scope>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-entitymanager</artifactId>
<version>4.0.1.Final</version>
</dependency>
<dependency>
<scope>compile</scope>
<groupId>net.sf.ehcache</groupId>
<artifactId>ehcache</artifactId>
<version>2.5.0</version>
</dependency>
<dependency>
<scope>compile</scope>
<groupId>jasperreports</groupId>
<artifactId>jasperreports</artifactId>
<version>3.5.3</version>
</dependency>
...many dependencies below this point
When I save the changes, Eclipse builds the workspace and gives me an error on the opening <dependency> tag for EhCache 2.5:
Missing artifact net.sf.ehcache:ehcache:jar:2.5.0
So I figured that perhaps v.2.5.0 has something wrong with it, and repeated the same for 2.4.7 (the last 2.4.x release before 2.5.0). Same deal.
Since I'm so new to Maven, I don't even know where to begin looking. I tried Project >> Clean and even restarted Eclipse to see if it was just a typical Eclipse "quirk". Nope.
I am thinking:
Could EhCache be publishing bad JARs to the Maven repo?
Could Maven Repo have something wrong with it?
Could this be due to something else configured wrong in my pom.xml?
Could this be a "JAR hell" issue where I have a conflict somewhere on my dependency graph?
How would SO start tackling this problem? Thanks in advance!

It is usually safer to refer to search.maven.org. Dependency from there:
<dependency>
<groupId>net.sf.ehcache</groupId>
<artifactId>ehcache</artifactId>
<version>2.5.0</version>
<type>pom</type>
</dependency>
Mind type pom. From module's pom:
This is a pom artifact to pull in ehcache-core and ehcache-terracotta
for clustering. Make sure to set 'type' to 'pom' in your dependency.
Aparently when someone does not need terracotta, ehcache-core will do perfectly fine as other answer states.

They use ehcache-core in the official documentation. Maven Central does not have a jar artifact for ehcache 2.5 which explains your error message.
Using ehcache-core changes the dependency to:
<dependency>
<groupId>net.sf.ehcache</groupId>
<artifactId>ehcache-core</artifactId>
<version>2.5.0</version>
</dependency>
Which successfully downloads on my machine (ehcache does not).

I dropped this into IntelliJ and it found it. I suspect there is something wrong with your settings. Try creating a project with only this dependency in it. If it fails to download, I would check your setting. e.g. .m2/settings.xml Are you using a Nexus server or maven proxy/cache?
BTW: A simpler way to search for JARs is to use http://mvnrepository.com/ which will find all the available versions and show you the XML you need to add.

java ee api is missing on project classpath while using httpunit for servlet testing in maven

I want to run the servlet testing example available here using maven. Javaee web api should be declared as provided:
<dependency>
<groupId>javax</groupId>
<artifactId>javaee-web-api</artifactId>
<version>6.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>httpunit</groupId>
<artifactId>httpunit</artifactId>
<version>1.7</version>
<scope>test</scope>
</dependency>
However, one of the tests in the example throws ServletException. NetBeans complains that java ee api is missing on project classpath. How does one solve this issue?
EDIT
It is not a NetBeans issue, it is a maven issue.

Now this is the most debilitating issue I have ever faced in my Java days. And it is followed by the most ridiculous workaround I have ever seen, ever:
<dependency>
<groupId>httpunit</groupId>
<artifactId>httpunit</artifactId>
<version>1.7</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>javax</groupId>
<artifactId>javaee-web-api</artifactId>
<version>6.0</version>
<scope>provided</scope>
</dependency>
Yes, permute the declaration of dependencies in the pom.xml (see here for "why") and make javaee-web-api last.

It means that maven (or netbeans...I haven't used netbeans in 10 years), couldn't download or find that artifact in the local repository.
The scope provided means: I need the jar to compile my source code, but don't bundle the jar in the final package.