java - 如何在 Spring 框架上使用抽象类？

Question

我正在学习如何使用 Spring Boot 编写代码。然后，当我尝试编写使用抽象类的代码时，出现如下错误。

Description:

Parameter 0 of constructor in com.in28minutes.spring.practice.springmasterclasspractice.devicefactory.LaptopManufacturingProcess required a bean of type 'java.lang.String' that could not be found.

Action:
Consider defining a bean of type 'java.lang.String' in your configuration.

你们能给我建议如何解决这个错误吗？

Spring 启动:v2.1.4 java :10.0.2Maven:3.6.0

SpringMasterClassPracticeDeviceFactoryApplication 类

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

@SpringBootApplication
public class SpringMasterClassPracticeDeviceFactoryApplication {

    private static Logger LOGGER = LoggerFactory.getLogger(SpringMasterClassPracticeDeviceFactoryApplication.class);

    public static void main(String[] args) {
        ConfigurableApplicationContext applicationContext = SpringApplication
                .run(SpringMasterClassPracticeDeviceFactoryApplication.class, args);
        ManufacturingImpl manufacturingImpl = applicationContext.getBean(ManufacturingImpl.class);

        System.out.println(manufacturingImpl);
        // manufacturingImpl.manifactureProduct("Laptop Process");

        LOGGER.info("{}", manufacturingImpl);

    }

}

ManufacturingImpl 类

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;

@Component
public class ManufacturingImpl {

    @Autowired
    @Qualifier("laptop")
    private GeneralManufacturingProcess generalManufacturingProcess;

    public void manifactureProduct(String processName) {
        System.out.println(generalManufacturingProcess);
        generalManufacturingProcess.launchProcess();
    }
}

GeneralManufacturingProcess 类

public abstract class GeneralManufacturingProcess {

    private String processName;

    public GeneralManufacturingProcess(String processName) {
        this.processName = processName;
    }

    public String getProcessName() {
        return processName;
    }

    public void launchProcess() {
        if (processName != null && !processName.isEmpty()) {
            assembleDevice();
            testDevice();
            packageDevice();
            storeDevice();
        } else {
            System.out.println("No process name was specified");
        }
    }

    protected abstract void assembleDevice();

    protected abstract void testDevice();

    protected abstract void packageDevice();

    protected abstract void storeDevice();
}

LaptopManufacturingProcess 类

import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;

@Component
@Qualifier("laptop")
public class LaptopManufacturingProcess extends GeneralManufacturingProcess {

    public LaptopManufacturingProcess(String processName) {
        super(processName);
    }

    @Override
    protected void assembleDevice() {
        System.out.println("Assembled laptop: " + getProcessName());
    }

    @Override
    protected void testDevice() {
        System.out.println("Tested laptop: " + getProcessName());
    }

    @Override
    protected void packageDevice() {
        System.out.println("Packaged laptop: " + getProcessName());
    }

    @Override
    protected void storeDevice() {
        System.out.println("Stored laptop: " + getProcessName());
    }
}

Answer 1

有多种方法可以解决这个问题。问题是，Spring 框架尝试使用单个构造函数创建 LaptopManufacturingProcess 的实例，该构造函数接受一个字符串。因此框架试图将 String 类型的 Bean Autowiring 到构造函数中，但这根本不起作用。基本上，您可以执行以下操作:

• 创建一个无参数构造函数，并将硬编码字符串传递给父构造函数:

public LaptopManufacturingProcess() {
  super("String");
}

• 添加 @Value-Annotation 以从 PropertySource 读取字符串:

public LaptopManufacturingProcess(@Value("${property.key.here}") String processName) {
  super(processName);
}

• 创建一个 Factory Bean 以按需创建 GeneralManufacturingProcess 实例