MapStruct internal error: NullPointerException solution

introduction

In Java development, MapStruct is a very popular object mapping tool. It generates mapping code at compile time by annotation processor, greatly simplifying the conversion operations between objects. However, developers may encounter some tricky errors, especially internal errors (Internal Error). This article will analyze a common internal error of MapStruct - NullPointerException in detail, and provide a series of solutions to help developers quickly locate and solve problems.

Problem description

When compiling a Java project, you may encounter the following error message:

E:\workspace\yien\ysx-mediamanager\mediamanager\src\main\java\com\media\utils\:12:8
java: Internal error in the mapping processor: 
    at (:180)
    at (:151)
    at (:127)
    at (:120)
    at (:98)
    at .<init>(:59)
    at (:222)
    at (:162)
    at $(:206)
    ...

As can be seen from the error message, the problem occurs in MapStructIn the method, it is specifically in line 180. This is a typicalNullPointerException, means that the code tries to access the properties or methods of an empty object.

Problem analysis

1. Error location

The error occurred inIn the method, it is specifically in line 180. This is aNullPointerException, means that the code tries to access the properties or methods of an empty object.

2. Call stack

The call stack shows that the error occurs during the version information processing of the MapStruct library, specifically when trying to obtain the library name and compiler information.

3. Possible Causes

• MapStruct version issue: It may be that the version of the MapStruct library is incompatible with the current project environment.
• Dependency missing: Some necessary dependencies or configuration files may be missing.
• Environmental issues: Probably a configuration issue with Java compiler or build tools such as Maven or Gradle.

Solution

1. Check the MapStruct version

Make sure the MapStruct version used is compatible with other dependencies of the project. You can try upgrading or downgrading the MapStruct version.

For example,(Maven) orCheck the version of MapStruct in (Gradle).

Maven configuration example:

<dependency>
    <groupId></groupId>
    <artifactId>mapstruct</artifactId>
    <version>1.5.</version>
</dependency>
<dependency>
    <groupId></groupId>
    <artifactId>mapstruct-processor</artifactId>
    <version>1.5.</version>
    <scope>provided</scope>
</dependency>

Gradle configuration example:

dependencies {
    implementation ':mapstruct:1.5.'
    annotationProcessor ':mapstruct-processor:1.5.'
}

2. Check dependencies

Make sure that all necessary dependencies are correctly added to the project. Especially the dependencies related to MapStruct, such asmapstruct-processor。

3. Clean up and rebuild the project

Clean the project and rebuild it to ensure that all compiled files are up to date.

Can be used in Mavenmvn clean install, can be used in Gradlegradle clean build。

4. Check the compiler configuration

Make sure the Java compiler is configured correctly, especially the annotation processor-related configuration.

In Maven, you canConfigure the annotation processor:

<build>
    <plugins>
        <plugin>
            <groupId></groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
            <configuration>
                <annotationProcessorPaths>
                    <path>
                        <groupId></groupId>
                        <artifactId>mapstruct-processor</artifactId>
                        <version>${}</version>
                    </path>
                </annotationProcessorPaths>
            </configuration>
        </plugin>
    </plugins>
</build>

5. Check IDE configuration

If using an IDE (such as IntelliJ IDEA), make sure the annotation processor of the IDE is configured correctly.

In IntelliJ IDEA, you can enable annotation processor in File -> Settings -> Build, Execution, Deployment -> Compiler -> Annotation Processors.

6. View the MapStruct Documentation

Refer to the official MapStruct documentation to see if there are any relevant configuration or version compatibility instructions.

Sample code

Here is a simple MapStruct mapping example showing how to use MapStruct for object mapping in your project.

public class User {
    private String name;
    private int age;

    // Getters and Setters
}

public class UserDTO {
    private String name;
    private int age;

    // Getters and Setters
}

import ;
import ;

@Mapper
public interface UserMapper {
    UserMapper INSTANCE = ();

    UserDTO userToUserDTO(User user);
}

import ;
import ;
import ;

public class MappingUtil {
    public static void main(String[] args) {
        User user = new User();
        ("John Doe");
        (30);

        UserDTO userDTO = (user);
        ("UserDTO Name: " + ());
        ("UserDTO Age: " + ());
    }
}

in conclusion

Through the detailed analysis and solutions in this article, developers can better understand and resolve the internal error of MapStruct - NullPointerException. The key is to make sure the MapStruct version is compatible with the project environment, check for dependencies, clean up and rebuild the project, and configure the compiler and IDE correctly. I hope this article can help developers better use MapStruct in actual projects and improve development efficiency.

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