问题描述
我正在使用以下两个教程将QueryDSL与Spring Boot Project集成在一起,但是我一直在得到Null指针异常。
参考教程:
- http://www.querydsl.com/static/querydsl/4.4.0/reference/html_single/#d0e137
- https://www.baeldung.com/intro-to-querydsl
我已经尝试过各种StackOverflow问题中给出的解决方案,但是没有用。以下是我尝试过的一些解决方案。
- Spring with Querydsl : Null Pointer Exception ---这无关紧要,因为id字段本身是整数
- NullPointerException on QueryDSL where clause ---这无关紧要,因为我正在第一层上使用查询。
- https://jira.spring.io/browse/DATAJPA-1290-与使用单个ID无关
代码:
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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.3.4.RELEASE</version>
<relativePath /> <!-- lookup parent from repository -->
</parent>
<groupId>com.stock.prediction</groupId>
<artifactId>StockPrediction</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>StockPrediction</name>
<description>Startup Application</description>
<properties>
<java.version>11</java.version>
<querydsl.version>4.1.3</querydsl.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-freemarker</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.apache.poi</groupId>
<artifactId>poi</artifactId>
<version>4.1.0</version>
</dependency>
<dependency>
<groupId>org.apache.poi</groupId>
<artifactId>poi-ooxml</artifactId>
<version>4.1.0</version>
</dependency>
<!-- For query DSL -->
<dependency>
<groupId>com.querydsl</groupId>
<artifactId>querydsl-apt</artifactId>
<version>${querydsl.version}</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>com.querydsl</groupId>
<artifactId>querydsl-jpa</artifactId>
<version>${querydsl.version}</version>
</dependency>
<dependency>
<groupId>javax.inject</groupId>
<artifactId>javax.inject</artifactId>
<version>1</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.6.1</version>
</dependency>
<!-- End Query Dsl -->
<dependency>
<groupId>commons-validator</groupId>
<artifactId>commons-validator</artifactId>
<version>1.6</version>
</dependency>
<dependency>
<groupId>MysqL</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.security</groupId>
<artifactId>spring-security-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<groupId>com.mysema.maven</groupId>
<artifactId>apt-maven-plugin</artifactId>
<version>1.1.2</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>
</plugins>
</build>
</project>
实体:
package com.stock.entities;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
@Entity
public class ModeOfAcquisitionEntity {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
private String name;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
存储库:
package com.stock.Repositories;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import org.springframework.stereotype.Repository;
import com.querydsl.jpa.impl.JPAQuery;
import com.stock.entities.ModeOfAcquisitionEntity;
import com.stock.entities.QModeOfAcquisitionEntity;
@Repository
public class ModeImplementation {
@PersistenceContext
private EntityManager em;
JPAQuery<?> query = new JPAQuery<>(em);
public String getFilterData() {
QModeOfAcquisitionEntity mode = QModeOfAcquisitionEntity.modeOfAcquisitionEntity;
ModeOfAcquisitionEntity entity = query.select(mode).fetchFirst();
return entity.getName();
}
}
启动错误:
Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2020-10-13 23:40:37.397 ERROR 20644 --- [ main] o.s.boot.SpringApplication : Application run Failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'modeImplementation' defined in file [C:\javaprojects\StockPrediction\target\classes\com\stock\Repositories\ModeImplementation.class]: Instantiation of bean Failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.stock.Repositories.ModeImplementation]: Constructor threw exception; nested exception is java.lang.NullPointerException
at org.springframework.beans.factory.support.AbstractAutowireCapablebeanfactory.instantiateBean(AbstractAutowireCapablebeanfactory.java:1318) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapablebeanfactory.createBeanInstance(AbstractAutowireCapablebeanfactory.java:1213) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapablebeanfactory.doCreateBean(AbstractAutowireCapablebeanfactory.java:556) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapablebeanfactory.createBean(AbstractAutowireCapablebeanfactory.java:516) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.beans.factory.support.Abstractbeanfactory.lambda$doGetBean$0(Abstractbeanfactory.java:324) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.beans.factory.support.Abstractbeanfactory.doGetBean(Abstractbeanfactory.java:322) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.beans.factory.support.Abstractbeanfactory.getBean(Abstractbeanfactory.java:202) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.beans.factory.support.DefaultListablebeanfactory.preInstantiateSingletons(DefaultListablebeanfactory.java:897) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.finishbeanfactoryInitialization(AbstractApplicationContext.java:879) ~[spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551) ~[spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:143) ~[spring-boot-2.3.4.RELEASE.jar:2.3.4.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:758) ~[spring-boot-2.3.4.RELEASE.jar:2.3.4.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:750) ~[spring-boot-2.3.4.RELEASE.jar:2.3.4.RELEASE]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) ~[spring-boot-2.3.4.RELEASE.jar:2.3.4.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) ~[spring-boot-2.3.4.RELEASE.jar:2.3.4.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1237) ~[spring-boot-2.3.4.RELEASE.jar:2.3.4.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) ~[spring-boot-2.3.4.RELEASE.jar:2.3.4.RELEASE]
at com.stock.StockPredictionApplication.main(StockPredictionApplication.java:10) ~[classes/:na]
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.stock.Repositories.ModeImplementation]: Constructor threw exception; nested exception is java.lang.NullPointerException
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:217) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:87) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapablebeanfactory.instantiateBean(AbstractAutowireCapablebeanfactory.java:1310) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
... 18 common frames omitted
Caused by: java.lang.NullPointerException: null
at com.querydsl.jpa.impl.JPAProvider.getTemplates(JPAProvider.java:61) ~[querydsl-jpa-4.1.3.jar:na]
at com.querydsl.jpa.impl.JPAQuery.<init>(JPAQuery.java:48) ~[querydsl-jpa-4.1.3.jar:na]
at com.stock.Repositories.ModeImplementation.<init>(ModeImplementation.java:18) ~[classes/:na]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:na]
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490) ~[na:na]
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:204) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE]
... 20 common frames omitted
解决方法
我能够找到解决方案。在存储库中,我应该在方法内部创建JPAQuery对象,而不是将其声明为类变量。
所以新的存储库应该是
package com.stock.Repositories;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import org.springframework.stereotype.Repository;
import com.querydsl.jpa.impl.JPAQuery;
import com.stock.entities.ModeOfAcquisitionEntity;
import com.stock.entities.QModeOfAcquisitionEntity;
@Repository
public class ModeImplementation {
@PersistenceContext
private EntityManager em;
public String getFilterData() {
JPAQuery<?> query = new JPAQuery<>(em);
QModeOfAcquisitionEntity mode =
QModeOfAcquisitionEntity.modeOfAcquisitionEntity;
ModeOfAcquisitionEntity entity = query.select(mode).fetchFirst();
return entity.getName();
}
}
如果有人想知道为什么我要使用1.1.2版的apt-maven-plugin,那是因为我正在使用Spring工具套件(STS)进行开发,而1.1.3版在STS中无法正常工作。