What I've done
I created a maven project with IntelliJ IDEA, following a tutorial.
The tiny project in JDK11 is to demo (for myself) how com.google.code.gson serializes an object to a json string.
This project's POM is:
<?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/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>mig</groupId>
<artifactId>mia</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<!-- Gson: Java to Json conversion -->
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.6</version>
</dependency>
</dependencies>
<properties>
<maven.compiler.release>11</maven.compiler.release>
</properties>
<build>
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
In Employee.java, I did generated the setters and getters though I don't put them here to save some space.
public class Employee
{
private Integer id;
private String firstName;
private String lastName;
private List<String> roles;
public Employee(){
}
public Employee(Integer id, String firstName, String lastName, Date birthDate){
this.id = id;
this.firstName = firstName;
this.lastName = lastName;
}
//Getters and setters
@Override
public String toString()
{
return "Employee [id=" + id + ", firstName=" + firstName + ", " +
"lastName=" + lastName + ", roles=" + roles + "]";
}
}
O2Json.java
package mig;
import java.util.Arrays;
import com.google.gson.*;
public class O2Json {
public static void main(String[] args) throws Exception{
Employee employee = new Employee();
employee.setId(1);
employee.setFirstName("Lokesh");
employee.setLastName("Gupta");
employee.setRoles(Arrays.asList("ADMIN", "MANAGER"));
System.out.println(employee.toString());
Gson gson = new Gson();
System.out.println(gson.toJson(employee));
}
}
The project consists of the following standard project structure
mvn_idea
├── pom.xml
└── src
├── main
│ ├── java
│ │ ├── Employee.java
│ │ └── O2Json.java
│ └── resources
└── test
└── java
Everything goes well with IntelliJ IDEA on my mac when I run the app using Run menu command of IDEA.
This command generates an executable JAR with IntelliJ IDEA
/Library/Java/JavaVirtualMachines/adoptopenjdk-11.jdk/Contents/Home/bin/java -Dmaven.multiModuleProjectDirectory=/Users/ubuntu/sourcecode/mvn_idea "-Dmaven.home=/Applications/IntelliJ IDEA CE.app/Contents/plugins/maven/lib/maven3" "-Dclassworlds.conf=/Applications/IntelliJ IDEA CE.app/Contents/plugins/maven/lib/maven3/bin/m2.conf" "-javaagent:/Applications/IntelliJ IDEA CE.app/Contents/lib/idea_rt.jar=65438:/Applications/IntelliJ IDEA CE.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath "/Applications/IntelliJ IDEA CE.app/Contents/plugins/maven/lib/maven3/boot/plexus-classworlds-2.5.2.jar" org.codehaus.classworlds.Launcher -Didea.version2019.1.3 install
However, this method is not as convenient on a Ubuntu server which I connect via SSH.
So I tried to do the job with the command line tool mvn.
mvn package seemed to work well
[INFO] Building jar: /Users/ubuntu/sourcecode/mvn_idea/target/mia-1.0-SNAPSHOT.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 01:13 min
[INFO] Finished at: 2021-05-16T09:41:04+08:00
[INFO] Final Memory: 18M/74M
[INFO] ------------------------------------------------------------------------
However, when I tried to run the app, the error showed up
$ java -cp target/mia-1.0-SNAPSHOT.jar mig.O2Json
mig.Employee [id=1, firstName=Lokesh, lastName=Gupta, roles=[ADMIN, MANAGER]]
Exception in thread "main" java.lang.NoClassDefFoundError: com/google/gson/Gson
at mig.O2Json.main(O2Json.java:15)
Caused by: java.lang.ClassNotFoundException: com.google.gson.Gson
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:636)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:182)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:519)
... 1 more
Questions
How do I fix this error?
Update
Here is the new version of POM
<?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/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>mig</groupId>
<artifactId>mia</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<!-- Gson: Java to Json conversion -->
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.6</version>
</dependency>
</dependencies>
<properties>
<maven.compiler.release>11</maven.compiler.release>
</properties>
<build>
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
</plugin>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
I executed mvn clean, mvn package and java -cp target/mia-1.0-SNAPSHOT.jar mig.O2Json and got the same error.
I also tried mvn clean compile assembly:single and java -cp target/mia-1.0-SNAPSHOT.jar mig.O2Json and got the same error.
