Spring：不断收到 java.lang.ClassNotFoundException：org.springframework.expression.ParserContext答案

【问题标题】：Spring: Keep getting java.lang.ClassNotFoundException: org.springframework.expression.ParserContextSpring：不断收到 java.lang.ClassNotFoundException：org.springframework.expression.ParserContext
【发布时间】：2021-08-15 08:36:34
【问题描述】：

我是 Spring 新手，刚刚使用注释做了一个小程序，但我不断收到标题和“AnnotationConfigApplicationContext prepareRefresh”中提到的错误。

Employee.java

package com.springdemo; 
import org.springframework.stereotype.Component;
@Component
public class Employee {

 int id;
String name,phone,dept;

public Employee() {}
public Employee(int id,String name,String phone,String dept) {
    this.id=id;
    this.name=name;
    this.phone=phone;
    this.dept=dept;
}
@Override
public String toString() {
    return "Employee [id=" + id + ", name=" + name + ", phone=" + phone + ", dept=" + dept + "]";
}

Main.java

package com.springdemo;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class Main {

public static void main(String[] args) {
    ApplicationContext context = new AnnotationConfigApplicationContext(EmployeeConfig.class);
    Employee emp = context.getBean(Employee.class);
    System.out.println(emp);
}}

EmployeeConfig.java

package com.springdemo;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan(basePackages= {"com.springdemo"})
public class EmployeeConfig {

@Bean
public Employee getEmployee() {
    return new Employee(101,"Pradhyumn","9057672243","Analyst");
}}

【问题讨论】：

通常这些错误是由于混合了来自不同版本的 Spring 的 jar。
如果这是一个 maven 项目，pom.xml 可能会有所帮助。或者，如果是单模块 gradle 项目，build.gradle 会有所帮助。请将它们也包括在问题中。

标签： java spring eclipse spring-boot gradle

【解决方案1】：

为什么要让事情变得复杂？只需使用@Component、@Service、@Repository 或@Configuration 注释类创建单个bean。在您需要的任何地方自动连接它们。与其让main方法实现AnnotationConfigApplicationContext，不如在你的应用类上使用@SpringBootApplication，直接获取ApplicationContext。

另外，在您的代码中，您使用 @Component 注释了 Employee 类，然后在您的配置类中再次为 Employee 创建一个 bean。

您可能想查看以下代码的表示形式。

@SpringBootApplication public class DemoApplication
{

    public static void main(String[] args)
    {
        ApplicationContext applicationContext = SpringApplication.run(DemoApplication.class, args);
        SomeService service = applicationContext.getBean(SomeService.class);
        service.doSth(args);
    }

}

@Service
@ConditionalOnBean({EnableConfiguration.class, Employee.class})
class SomeService {

    @Autowired
    private Employee employee;

    public void doSth(String[] args){
        System.out.println(employee.toString());
    }
}

public class Employee
{

    int id;
    String name, phone, dept;

    public Employee()
    {
    }

    public Employee(int id, String name, String phone, String dept)
    {
        this.id = id;
        this.name = name;
        this.phone = phone;
        this.dept = dept;
    }

    @Override public String toString()
    {
        return "Employee [id=" + id + ", name=" + name + ", phone=" + phone + ", dept=" + dept + "]";
    }
}

@Configuration
public class EnableConfiguration
{

    @Bean
    public Employee getEmployee() {
        return new Employee(101,"Pradhyumn","91223123222","Analyst");
    }
}

pom.xml

<?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>2.5.0</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

【讨论】：