Spring Boot Java Config实践示例：从零构建一个简单的Web应用

在Spring Boot中，Java Config是一种使用Java类来配置Spring容器的方式，替代传统的XML配置文件。Java Config不仅更加类型安全，还提供了更好的IDE支持和重构能力。以下是一个简单的Spring Boot Java Config代码示例。

假设我们有一个简单的Spring Boot应用，包含一个控制器、一个服务和一个配置类。

1. 创建Spring Boot主应用类

首先，创建一个Spring Boot主应用类，该类包含main方法，用于启动Spring Boot应用。

package com.example.demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}
package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}
package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

2. 创建配置类

接下来，创建一个Java配置类，用于定义Spring Bean。

package com.example.demo.config;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import com.example.demo.service.MyService;
@Configuration
public class AppConfig {
    @Bean
    public MyService myService() {
        return new MyServiceImpl();
    }
}
package com.example.demo.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import com.example.demo.service.MyService;

@Configuration
public class AppConfig {

    @Bean
    public MyService myService() {
        return new MyServiceImpl();
    }
}
package com.example.demo.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import com.example.demo.service.MyService;

@Configuration
public class AppConfig {

    @Bean
    public MyService myService() {
        return new MyServiceImpl();
    }
}

3. 创建服务接口和实现类

定义一个服务接口及其实现类。

package com.example.demo.service;
public interface MyService {
    String sayHello(String name);
}
package com.example.demo.service.impl;
import com.example.demo.service.MyService;
import org.springframework.stereotype.Service;
@Service
public class MyServiceImpl implements MyService {
    @Override
    public String sayHello(String name) {
        return "Hello, " + name + "!";
    }
}
package com.example.demo.service;

public interface MyService {
    String sayHello(String name);
}

package com.example.demo.service.impl;

import com.example.demo.service.MyService;
import org.springframework.stereotype.Service;

@Service
public class MyServiceImpl implements MyService {

    @Override
    public String sayHello(String name) {
        return "Hello, " + name + "!";
    }
}
package com.example.demo.service;

public interface MyService {
    String sayHello(String name);
}

package com.example.demo.service.impl;

import com.example.demo.service.MyService;
import org.springframework.stereotype.Service;

@Service
public class MyServiceImpl implements MyService {

    @Override
    public String sayHello(String name) {
        return "Hello, " + name + "!";
    }
}

注意：虽然我们在MyServiceImpl类上使用了@Service注解，这本身已经足够让Spring Boot识别并管理这个Bean。但在这个示例中，我们还是在AppConfig配置类中显式地定义了这个Bean，以展示如何使用Java Config。

4. 创建控制器

创建一个控制器类，用于处理HTTP请求。

package com.example.demo.controller;
import com.example.demo.service.MyService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class HelloController {
    private final MyService myService;
    @Autowired
    public HelloController(MyService myService) {
        this.myService = myService;
    }
    @GetMapping("/hello")
    public String sayHello(@RequestParam String name) {
        return myService.sayHello(name);
    }
}
package com.example.demo.controller;

import com.example.demo.service.MyService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    private final MyService myService;

    @Autowired
    public HelloController(MyService myService) {
        this.myService = myService;
    }

    @GetMapping("/hello")
    public String sayHello(@RequestParam String name) {
        return myService.sayHello(name);
    }
}
package com.example.demo.controller;

import com.example.demo.service.MyService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    private final MyService myService;

    @Autowired
    public HelloController(MyService myService) {
        this.myService = myService;
    }

    @GetMapping("/hello")
    public String sayHello(@RequestParam String name) {
        return myService.sayHello(name);
    }
}

5. 运行应用

现在，你可以运行DemoApplication类的main方法，启动Spring Boot应用。然后，访问http://localhost:8080/hello?name=YourName，你应该会看到类似Hello, YourName!的响应。

总结

以上示例展示了如何在Spring Boot中使用Java Config来配置Spring容器。通过使用@Configuration注解和@Bean注解，我们可以在Java类中定义Spring Bean，替代传统的XML配置文件。此外，Spring Boot还提供了许多自动配置功能，使得配置变得更加简单和高效。