Mapstruct 1.2.0.Final版本嵌入式类型转换失败求助

Hey there! Let's figure out why your embedded Job object is showing up as null in JobData after using MapStruct. Based on the error you shared (java.lang.AssertionError: Expected: is not null but: was null), here are the most common fixes and checks to run through:

1. Double-Check Your Embedded Class Annotations #

First, make sure your JPA annotations are set up correctly for the embedded type:

• Your Job class should be annotated with @Embeddable
• In JobData, the Job field needs @Embedded (you can use @AttributeOverrides if customizing column names, but that's optional for basic mapping)
• Example:

  @Embeddable
  public class Job {
      private Long id;
      private String title;
      // getters & setters
  }
  
  public class JobData {
      @Embedded
      private Job job;
      // other fields + getters & setters
  }
  

2. Verify MapStruct Mapper Configuration #

MapStruct won't guess nested mappings automatically if source and target paths don't align perfectly. Here's what to check:

• If your source object has flat fields (e.g., sourceJobId, sourceJobTitle) that need to map to JobData.job.id and JobData.job.title, add explicit @Mapping annotations:

  @Mapper
  public interface JobDataMapper {
      JobDataMapper INSTANCE = Mappers.getMapper(JobDataMapper.class);
  
      @Mapping(target = "job.id", source = "sourceJobId")
      @Mapping(target = "job.title", source = "sourceJobTitle")
      JobData mapToJobData(JobSource source);
  }
  

• If your source object already has a Job field, ensure the field name matches exactly (case-sensitive!) in both source and target. If they don't match, use @Mapping(target = "job", source = "sourceJobField") to link them.

3. Ensure Annotation Processing is Enabled in IntelliJ 2017 #

Even with the MapStruct plugin installed, IntelliJ might not generate mapper implementation classes correctly. Fix this by:

• Going to File > Settings > Build, Execution, Deployment > Compiler > Annotation Processors
• Checking the box that says Enable annotation processing
• Confirming the output directory for generated sources is set (usually target/generated-sources/annotations for Maven projects)
• Rebuilding your project after changing this setting—this forces MapStruct to generate the mapper code.

4. Validate Your Dependencies #

Make sure your build file (Maven/Gradle) includes the correct MapStruct dependencies, especially the annotation processor:

• For Maven, your pom.xml should have:

  <dependencies>
      <dependency>
          <groupId>org.mapstruct</groupId>
          <artifactId>mapstruct</artifactId>
          <version>1.3.1.Final</version> <!-- Use a compatible version -->
      </dependency>
  </dependencies>
  
  <build>
      <plugins>
          <plugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-compiler-plugin</artifactId>
              <version>3.8.1</version>
              <configuration>
                  <source>1.8</source> <!-- Match your Java version -->
                  <target>1.8</target>
                  <annotationProcessorPaths>
                      <path>
                          <groupId>org.mapstruct</groupId>
                          <artifactId>mapstruct-processor</artifactId>
                          <version>1.3.1.Final</version> <!-- Same as above -->
                      </path>
                  </annotationProcessorPaths>
              </configuration>
          </plugin>
      </plugins>
  </build>
  

• Mismatched versions between mapstruct and mapstruct-processor are a common cause of broken mappings.

5. Inspect the Generated Mapper Implementation #

MapStruct generates concrete implementations of your mapper interface—check it to see if it's actually populating the job field:

• In IntelliJ, navigate to target/generated-sources/annotations (for Maven)
• Find the generated class (e.g., JobDataMapperImpl)
• Check the mapToJobData method: if there's no code setting jobData.setJob(...), MapStruct didn't recognize the mapping. This points back to missing @Mapping annotations or incorrect field names.

Final Quick Check #

Make sure you're using the mapper correctly in your test:

• Use the INSTANCE field from your mapper interface (e.g., JobDataMapper.INSTANCE.mapToJobData(source))
• Avoid creating a new instance of the mapper directly—MapStruct handles instantiation via the Mappers factory.

Give these steps a try, and you should be able to track down why that job field is null!

内容的提问来源于stack exchange，提问作者StillLearningToCode