SpringBoot：JParepository Findbyid不起作用？即使考虑了可选包装器类

Question

您可以看到我有一种无法正常工作的Findbyid方法。尽管Findall方法效果很好。

我收到的错误消息：

java.lang.Error: Unresolved compilation problems: 
    Optional cannot be resolved to a type
    The method findById(Integer) from the type CrudRepository<Employee,Integer> refers to the missing type Optional

我很困惑，因为我正在其他堆栈流帖子中使用可选的包装程序类，以及我关注的教程。知道我做错了什么？employereepository.java

package Spring.RestProject.repository;


import org.springframework.data.jpa.repository.JpaRepository;

import Spring.RestProject.entity.Employee;

public interface EmployeeRepository extends JpaRepository<Employee, Integer> {

}

employeService.java

package Spring.RestProject.service;

import java.util.List;

import Spring.RestProject.entity.Employee;

public interface EmployeeService {
    Employee findById(int id);
    List<Employee> findAll();
}

employeeserviceImpl.java

package Spring.RestProject.service;

import java.util.List;
import java.util.Optional;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import Spring.RestProject.entity.Employee;
import Spring.RestProject.repository.EmployeeRepository;

@Service
public class EmployeeServiceImpl implements EmployeeService {
    
    EmployeeRepository employeeRepository;
    
    @Autowired
    public EmployeeServiceImpl (EmployeeRepository employeeRepository) {
        this.employeeRepository = employeeRepository;
    }
    
    @Override
    public Employee findById(int id) {
        
        Optional<Employee> result = employeeRepository.findById(id);
        Employee theEmployee;
        
        if(result.isPresent()) {
            theEmployee = result.get();
        } else {
            return null;
        }
        
        return theEmployee;
    }

    @Override
    public List<Employee> findAll() {
        return employeeRepository.findAll();
    }
}

Controller.java

package Spring.RestProject.restcontroller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import Spring.RestProject.entity.Employee;
import Spring.RestProject.service.EmployeeService;


@RestController
@RequestMapping("/api")
public class Controller {
    
    EmployeeService employeeService;
    
    @Autowired
    public Controller (EmployeeService employeeService) {
        this.employeeService = employeeService;
    }
    
    @GetMapping("/employees/{id}")
    public Employee findById(@PathVariable int id) {
        return employeeService.findById(id);
    } 
    
    @GetMapping("/employees")
    public List<Employee> findAll () {
        return employeeService.findAll();
    }

}

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>3.4.2</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>Spring</groupId>
    <artifactId>RestProject</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>RestProject</name>
    <description>Demo project for Spring Boot</description>
    <url/>
    <licenses>
        <license/>
    </licenses>
    <developers>
        <developer/>
    </developers>
    <scm>
        <connection/>
        <developerConnection/>
        <tag/>
        <url/>
    </scm>
    <properties>
        <java.version>23</java.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-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>com.mysql</groupId>
            <artifactId>mysql-connector-j</artifactId>
            <scope>runtime</scope>
        </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>

I安装了JDK 23，现在代码有效。我认为我什至没有正确安装JDK。感谢您的帮助。

Answer 1