Ytukyg

I have this pom.xml file:

<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>suman</groupId>

    <artifactId>suman</artifactId>

    <packaging>jar</packaging>

    <version>1.0-SNAPSHOT</version>

    <name>suman</name>

    <url>http://maven.apache.org</url>



    <properties>

        <maven.compiler.source>1.8</maven.compiler.source>

        <maven.compiler.target>1.8</maven.compiler.target>

    </properties>



    <dependencies>





        <dependency>

            <groupId>com.google.code.gson</groupId>

            <artifactId>gson</artifactId>

            <version>2.8.5</version>

        </dependency>



        <dependency>

            <groupId>junit</groupId>

            <artifactId>junit</artifactId>

            <version>4.12</version>

            <scope>test</scope>

        </dependency>





    </dependencies>

</project>

and I have this main file:

package suman;



import java.net.*;

import java.io.*;

import com.google.code.gson.*;  // can't find this lib





public class App {

    public static void main(String args) {



        Gson gson = new Gson();

        gson.toJson(1);            



    }

}

and then I install with:

$ mvn install -DskipTests

and I get this compile error:

[ERROR] Failed to execute goal
org.apache.maven.plugins:maven-compiler-plugin:3.1:compile
(default-compile) on project suman: Compilation failure: Compilation
failure: [ERROR]
/home/oleg/codes/oresoftware/oredoc/test/builds/java/gson/src/main/java/suman/App.java:[5,1]
package com.google.code.gson does not exist [ERROR]
/home/oleg/codes/oresoftware/oredoc/test/builds/java/gson/src/main/java/suman/App.java:[17,9]
cannot find symbol [ERROR] symbol: class Gson [ERROR] location:
class suman.App [ERROR]
/home/oleg/codes/oresoftware/oredoc/test/builds/java/gson/src/main/java/suman/App.java:[17,25]
cannot find symbol [ERROR] symbol: class Gson [ERROR] location:
class suman.App

Does anyone know why it can't find the gson libraries? seems really weird.

Ok so if I change it to:

import com.google.gson.*;

then it compiles, but then if I run it with java -jar, I get this runtime error:

Exception in thread "main" java.lang.NoClassDefFoundError:
com/google/gson/Gson
at suman.App.main(App.java:17) Caused by: java.lang.ClassNotFoundException: com.google.gson.Gson
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:583)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:190)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:499)
... 1 more

Most likely your local Maven repository does not have jar file for:

    <dependency>

        <groupId>com.google.code.gson</groupId>

        <artifactId>gson</artifactId>

        <version>2.8.5</version>

    </dependency>

try to look down from ~/.m2/repository/com/google/code/gson/gson/2.8.5 directory.

If there is no jar file like gson-2.8.5.jar - simple step delete whole directory.

With next build it will force Maven to try to download that artifact from your defined remote repositories and you will see how it passed.

Either it will download and all will be fine or it will not.

If not - then check your settings.xml (or pom file) about repository from where it can be downloaded ( at least in Maven repository listing (https://mvnrepository.com/artifact/com.google.code.gson/gson/2.8.5) it is https://mvnrepository.com/artifact/com.google.code.gson/gson

If you have that repository defined and you are behind corporate proxy - check your proxy settings for Maven in settings.xml

BTW: at run time you must have all needed jar files in class path as long as you build jar (not war or ear). As alternative with Maven you can build "fat jar" and all classes from all dependencies will be there, but be ready it will be a really big fat jar. :-)

Ok so I was building my project with

$ mvn install -DskipTests

and then running it with:

$ java -cp target/suman-1.0-SNAPSHOT.jar suman.App

but instead I should use mvn to run it, like so:

$ mvn exec:java -Dexec.mainClass="suman.App"

now it has the right jar files in the classpath. using the plain java command, it didn't know where to find the com.google.code.gson jar file.

As an aside, I don't know why this fails to compile:

import com.google.code.gson.*;

but this succeeds:

import com.google.gson.*;

according to the pom.xml file, I would think the former not that latter would be correct.