How to Resolve java.lang.NoClassDefFoundError: javax/xml/soap/SOAPException in Java Web Services?

How can I troubleshoot the java.lang.NoClassDefFoundError: javax/xml/soap/SOAPException when running a Spring Web Service from a JAR file?

// Example SOAP request code here
String soapRequest = "<soapenv:Envelope xmlns:soapenv='http://schemas.xmlsoap.org/soap/envelope/'><soapenv:Body>...</soapenv:Body></soapenv:Envelope>";

The exception `java.lang.NoClassDefFoundError: javax/xml/soap/SOAPException` typically indicates that the Java Runtime Environment (JRE) cannot find the specified class at runtime. This issue is often encountered when packaging Java applications into JAR files, especially when certain libraries are not included in the build.

// Maven Shade Plugin Example to create an uber JAR
<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-shade-plugin</artifactId>
            <version>3.2.4</version>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>shade</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Causes

• The JAR file does not include the necessary dependencies for Java EE APIs such as SOAP.
• The classpath is not correctly configured when running the application.
• The Spring Web Service project is not correctly set up to include external libraries.

Solutions

• Ensure that all necessary dependencies are included in your JAR file. You may need to use a tool like Maven or Gradle to manage your dependencies effectively.
• For Maven users, include the following dependency in your `pom.xml`: ```xml <dependency> <groupId>javax.xml.soap</groupId> <artifactId>javax.xml.soap-api</artifactId> <version>1.4.0</version> </dependency> <dependency> <groupId>com.sun.xml.messaging</groupId> <artifactId>javax.xml.soap</artifactId> <version>1.4.0</version> </dependency> ```
• If you are using Gradle, add the following in your `build.gradle`: ```groovy implementation 'javax.xml.soap:javax.xml.soap-api:1.4.0' implementation 'com.sun.xml.messaging:javax.xml.soap:1.4.0' ```
• Check that your packaging includes all necessary dependencies. If using Maven, switching to the `jar-with-dependencies` packaging type may resolve the issue.

Mistake: Forgetting to include SOAP dependencies in the project's build configuration.

Solution: Always check your project's build file (like pom.xml or build.gradle) to ensure all required dependencies are present.

Mistake: Running the JAR without dependencies needed for SOAP, which leads to runtime exceptions.

Solution: Use a packaging plugin like Maven Shade or Spring Boot's fat JAR feature to bundle all dependencies.