Develop Reference

Maven multimodule project tries to download inner dependency from repository

I have a classical multimodule project with cross dependency
parent pom:
<modules>
<module>mod1</module>
<module>mod2</module>
</modules>
...
<dependencyManagement>
<dependencies>
<dependency>
<groupId>grp</groupId>
<artifactId>mod1</artifactId>
<version>${project.version}</version>
</dependency>
...
mod2 pom:
<dependencies>
<dependency>
<groupId>grp</groupId>
<artifactId>mod1</artifactId>
</dependency>
...
It builds mvn clean install fine, however when CI runs sonar using mvn sonar:sonar ... the maven tries to download mod1 snapshot dependency from repo, which supposed to be part of the same reactor.
Downloading from nexus: http://...mod1/1.0.0-SNAPSHOT/maven-metadata.xml
And it most cases it could not find the snapshot as it was not deployed yet, but it just keeps going. However it slows down the build as I have several modules and each takes a while to make a roundtrip to repository.
Why?

I had a very similar problem: mvn install was working fine, mvn sonar:sonar wasn't.
In my case, it was a test dependency:
<dependency>
<groupId>grp</groupId>
<artifactId>mod2</artifactId>
<version>${project.version}</version>
<type>test-jar</type>
<scope>test</scope>
</dependency>
It was solved by adding test-compile to the mvn command:
mvn test-compile sonar:sonar
I got the tip from this answer: https://stackoverflow.com/a/57226037/5269825
I guess maven needs something (like compile or compile-test) to know that the dependency is another submodule.

Missing Maven Dependency and can not import class

I have created a new maven project by choosing org.apache.maven.archtypes maven.archtype.webapp.
I perform the below commands:
right click pom > maven clean
right click pom > maven install.
check maven user setting file
right click on project > maven update.
but maven dependency library is not added into libraries folder although a build success message has been output.
[INFO] Scanning for projects...
<p>
[INFO] Using the builder org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder with a thread count of 1
[INFO] BUILD SUCCESS
[INFO] Total time: 2.248 s
[INFO] Finished at: 2018-06-07T09:40:57+03:00
[INFO] Final Memory: 8M/20M
Here's my pom file, e.g dependency mvnrepository.com/artifact/com.fasterxml.jackson.datatype/jackson-datatype-
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0http://maven.apache. rg/xsd/maven-4.0.0.xsd">
<groupId>test</groupId>
<artifactId>maven.test</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>maven.test Maven Webapp</name>
<!-- FIXME change it to the project's website -->
<url>http://www.example.com</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.7</maven.compiler.source>
<maven.compiler.target>1.7</maven.compiler.target>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.datatype/jackson-datatype-jsr310 -->
<dependency>
<groupId>com.fasterxml.jackson.datatype</groupId>
<artifactId>jackson-datatype-jsr310</artifactId>
<version>2.9.5</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.16</version>
<scope>provided</scope>
</dependency>
</dependencies>
</project>
Here's my library screenshot without maven dependency

As Amer mentioned , do a maven update for your project, if it doest work the try with different network(either use mobile phone network or home network) to update project then do a eclipse clean(not maven clean) for that project then do a maven install. sometimes network block the jar file to download

right click on the project -> maven -> update project

I saw screen shot you attached but there is not any folder called "Maven Dependencies". So please try one option it may solve your problem...right click on project -> configure -> convert to maven.

go to the source folder of the project using cmd and
run maven command:
mvn clean install (this command won't work unless you specified path to maven/bin folder in path of system variables)
be sure you're not beyond the proxy, if you are, then you should configure maven to work with it. Link to how to configure a proxy in maven

How to bundle/package latest version of custom library in maven web project without updating pom.xml?

I have a custom library - Dao.jar which contains the database persistence logic.
I push this jar to artifactory with new version each time there is a change in code as shown below :
mvn install:install-file -Dfile=C:\*****\target\Dao.jar -DgroupId=non-public.com.karthik -DartifactId=dao -Dversion=2.0 -Dpackaging=jar
I have another maven web project which has a dependency on this jar. This jar is also packaged/bundled in the maven webapp project/war.
<dependency>
<groupId>non-public.com.karthik</groupId>
<artifactId>dao</artifactId>
<version>2.0</version>
</dependency>
Currently, I am changing the version of dao dependency in the pom.xml & re-building the maven webapp project each time a new version of Dao.jar is available in the artifactory.
Is there any option to build the maven project with the latest version of Dao.jar without manually changing the dependency version in the pom.xml?

When Maven searches for a dependency, it first checks the local repository (~/.m2/repository). If it's not found, it tries other resources, such as remote repositories defined in the POM file or in the settings file (~/.m2/settings.xml).
By that logic, if you try to use a version of a local project that's not yet installed to the local repository, Maven will never be able to find it to use in another project.
To avoid changing version numbers all the time and manually building both projects. You could create a parent POM for both projects. The parent would then be able to recognize that one of the child projects depends on the other and build them in the correct order.

Based on Luciano's inputs, I have created a multi-module maven project/parent POM with 2 modules(dao & web)
Parent
<groupId>com.karthik</groupId>
<artifactId>test</artifactId>
<packaging>pom</packaging>
<version>1.0-SNAPSHOT</version>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>3.0.5.RELEASE</version>
</dependency>
<dependency>
<groupId>oracle</groupId>
<artifactId>ojdbc6</artifactId>
<version>11.2.0.3</version>
</dependency>
..........
</dependencies>
</dependencyManagement>
<modules>
<module>web</module>
<module>dao</module>
</modules>
Child module # 1 - dao
<parent>
<groupId>com.karthik</groupId>
<artifactId>test</artifactId>
<version>1.0-SNAPSHOT</version>
</parent>
<artifactId>dao</artifactId>
<packaging>jar</packaging>
<dependencies>
<dependency>
<groupId>oracle</groupId>
<artifactId>ojdbc6</artifactId>
</dependency>
.........
</dependencies>
Child module # 2 - web(declared dao dependency in POM)
<parent>
<groupId>com.karthik</groupId>
<artifactId>test</artifactId>
<version>1.0-SNAPSHOT</version>
</parent>
<artifactId>web</artifactId>
<packaging>war</packaging>
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
</dependency>
<dependency>
<groupId>com.karthik</groupId>
<artifactId>dao</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>
.........
</dependencies>
When I run mvn package command at root path of parent pom, both modules - web.war and dao.jar are built. This method ensures always the latest version of dao.jar is packaged in web.war.

How to get all of required Apache POI library using Maven?

I have installed maven and I created a project using this command:
mvn archetype:generate -DgroupId=com.mycompany.app -DartifactId=my-app -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false
The result is there are 2 folder and 1 file created in my-app folder: src, target, and pom.xml.
Then I modify the pom.xml in order to get the all of required apache POI jars.
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.mycompany.my-app</groupId>
<artifactId>my-app</artifactId>
<packaging>jar</packaging>
<version>1.0-SNAPSHOT</version>
<name>my-app</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<!-- This is what I added -->
<dependency>
<groupId>org.apache.poi</groupId>
<artifactId>poi</artifactId>
<version>3.10-FINAL</version>
</dependency>
</dependencies>
</project>
Then I run:
mvn package
but no jars downloaded into the project folder although I got message "BUILD SUCCESS".

What you've done is correct. However, the poi jars won't download to your project folder but to your local Maven repository. This is exactly what Maven is supposed to do so that you don't have to manage many libraries/jars yourself and get all in a mess. If you do a search of your local Maven repository, you should find it there.
I also suggest you read up on how Maven uses external dependencies, this is all explained here:
http://maven.apache.org/guides/getting-started/index.html#How_do_I_use_external_dependencies
If you want to package up all of your dependent jars in to one big jar look here:
How can I create an executable JAR with dependencies using Maven?

Your project has a jar packaging type. Java not support nested jar and then maven package doesn't put any jar in your project . To do this you have to use Maven Assembly Plugin or use Spring-boot to make your uber jar

Mulit-module application maven

I've got multi module maven project, where main project depend on sub-module. Every dependency of sub-module is define by version like this: ${pom.version}. I use maven release plug-in. If I try to prepare release, I've got an error about missing version of sub-module.
Example:
main pom is on version 1.0, I try to release it. Maven build every sub-module to version 1.1, then try to build parent, and then crash. Because it can't find sub-module-1.1.
I don't know how to tell maven to build, and immediate install to local-repo every sub-module witch it build. I use maven2.
My pom:
<modelVersion>4.0.0</modelVersion>
<groupId>com.voncuver</groupId>
<artifactId>voncuver</artifactId>
<packaging>pom</packaging>
<version>1.1-SNAPSHOT</version>
<name>multimodule</name>
<modules>
<module>mod1</module>
<module>mod2</module>
</modules>
(...)
<dependencyManagement>
<dependencies>
<dependency>
<artifactId>mod1</artifactId>
<groupId>com.voncuver</groupId>
<version>${pom.version}</version>
</dependency>
<dependency>
<artifactId>mod2</artifactId>
<groupId>com.voncuver</groupId>
<version>${pom.version}</version>
</dependency>
</dependencies>
</dependencyManagement>
(...)

You should probably post a bit more of your project structure, but typically a multimodule project looks like this:
project
mod1
mod2
mod3
pom.xml
The main pom.xml would have "pom" packaging type, and have a section in it to build everything else:
<packaging>pom</packaging>
<modules>
<module>mod1</module>
<module>mod2</module>
<module>mod3</module>
</modules>
Then, the surest way to make sure things build properly is to execute:
mvn clean install
Without the "install", it's highly possible that things might not be found in the maven reactor, especially depending on what version of maven you are using (and a few other factors).