Spring Boot QueryDsl 返回原因：java.lang.UnsupportedOperationException：null

Question

code is as below

    QContinent continent = QContinent.continent;

    JPAQuery query = new JPAQuery(entityManager);


    query.from(continent).where(continent.name.eq("www"));
    List<Object> fetch = query.fetch();

    System.err.println("===" + fetch);

This returns
Caused by: java.lang.UnsupportedOperationException: null at java.util.Collections$UnmodifiableMap.put(Collections.java:1457) ~[na:1.8.0_191] at com.querydsl.jpa.JPQLSerializer.visitConstant(JPQLSerializer.java:327) ~[querydsl-jpa-4.2.1.jar:na] at com.querydsl.core.support.SerializerBase.visit(SerializerBase.java:221) ~[querydsl-core-4.3.1.jar:na] at com.querydsl.core.support.SerializerBase.visit(SerializerBase.java:36) ~[querydsl-core-4.3.1.jar:na] at com.querydsl.core.types.ConstantImpl.accept(ConstantImpl.Z93F725A07423FE1C889F448B33D2 1F46Z:140) ~[querydsl-core-4.3.1.jar:na]

Answer 1

As suggest by @user3388770, the reason is a mismatch of versions. In general,in your pom.xml / build.gradle do not specify a version for dependencies, that Spring already brings with except if you really need it for some reason.

You can find the used/compatible depencies here: https://docs.spring.io/spring-boot/docs/2.3.1.RELEASE/reference/html/appendix-dependency-versions.html (change the version according to your Spring version)

In case of your error, your dependencies should look like this ( build.gradle ):

plugins {
    id "org.springframework.boot" version "2.3.1.RELEASE"
    id 'io.spring.dependency-management' version '1.0.9.RELEASE'
    ...
}

apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'
...

dependencies {
   annotationProcessor(
            ...
            //some put a version below before ":jpa"; dont.
            "com.querydsl:querydsl-apt::jpa"
            ...
    )

    //just an example without version numbers as they are delivered with spring boot automatically
    compile "org.springframework.boot:spring-boot-starter-web"
    compile "org.springframework.boot:spring-boot-actuator"
    ...
    compile group: 'org.apache.httpcomponents', name: 'httpclient'
    compile 'org.thymeleaf.extras:thymeleaf-extras-java8time'

    //but most importantly this below 
    compile "com.querydsl:querydsl-jpa"
}

Answer 2

If you are in POM base project use these dependencies and apt plugin to resolve this issue with given versions

 <dependency>
    <groupId>com.querydsl</groupId>
    <artifactId>querydsl-apt</artifactId>
    <version>4.1.3</version>
    <scope>provided</scope>
</dependency>

<dependency>
    <groupId>com.querydsl</groupId>
    <artifactId>querydsl-jpa</artifactId>
    <version></version>
</dependency>

<plugin>
<groupId>com.mysema.maven</groupId>
<artifactId>apt-maven-plugin</artifactId>
<version>1.1.3</version>
<executions>
    <execution>
        <goals>
            <goal>process</goal>
        </goals>
        <configuration>
            <outputDirectory>target/generated-sources/java</outputDirectory>
            <processor>com.querydsl.apt.jpa.JPAAnnotationProcessor</processor>
        </configuration>
    </execution>
</executions>
</plugin>