Four ways to inject Service into Servlet in Spring

Method 1: Use @WebServlet and @Autowired

If you are using Servlet 3.0+ specification, you can use it directly@WebServletAnnotation to declare the Servlet and pass@AutowiredInject Service.

Implementation steps:

Configuring Servlet Scan Support
Make sure your project has Spring component scanning enabled, as well as Spring's integrated configuration with Servlet containers (such as through@SpringBootApplicationor manually configure Spring context).
Define Service Class

@Service
public class MyService {
    public String process() {
        return "Service processing...";
    }
}

Define Servlet class

@WebServlet(name = "myServlet", urlPatterns = "/myServlet")
public class MyServlet extends HttpServlet {

    @Autowired
    private MyService myService;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String result = ();
        ().write("Result from service: " + result);
    }
}

Spring configuration (optional)

If using Spring Boot, make sure@SpringBootApplicationAlready enabled@ServletComponentScan,as follows:

@SpringBootApplication
@ServletComponentScan
public class MyApplication {
    public static void main(String[] args) {
        (, args);
    }
}

Method 2: Register the Servlet through @Bean and inject dependencies

If you don't want to use@WebServletAnnotation can be done through Spring@ConfigurationRegister the Servlet as a Spring Bean into the Servlet container.

Implementation steps:

Define Service Class

@Service
public class MyService {
    public String process() {
        return "Service processing...";
    }
}

Define Servlet class

public class MyServlet extends HttpServlet {

    private final MyService myService;

    public MyServlet(MyService myService) {
         = myService;
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String result = ();
        ().write("Result from service: " + result);
    }
}

Configure Servlet Registration
In the Spring configuration class, register the Servlet bean and inject the Service:

@Configuration
public class ServletConfig {

    @Bean
    public ServletRegistrationBean<MyServlet> myServletRegistration(MyService myService) {
        return new ServletRegistrationBean<>(new MyServlet(myService), "/myServlet");
    }
}

Method 3: Through @Component and SpringBeanAutowiringSupport

If you are using a traditional servlet (such asServlet defined in SpringSpringBeanAutowiringSupportEnable dependency injection manually.

Implementation steps:

Define Service Class

@Service
public class MyService {
    public String process() {
        return "Service processing...";
    }
}

Define Servlet class

public class MyServlet extends HttpServlet {

    @Autowired
    private MyService myService;

    @Override
    public void init() throws ServletException {
        ();
        (this);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String result = ();
        ().write("Result from service: " + result);
    }
}

Configuring Servlet Container
If using, add Servlet configuration:

<servlet>
    <servlet-name>myServlet</servlet-name>
    <servlet-class></servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>myServlet</servlet-name>
    <url-pattern>/myServlet</url-pattern>
</servlet-mapping>

Spring Context Configuration
Make sure your Spring context is loaded into the Servlet container, for exampleDefine Spring Listener in:

<listener>
    <listener-class></listener-class>
</listener>
<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/</param-value>
</context-param>

Method 4: Spring Boot and ServletRegistrationBean

If you are using Spring Boot, it is recommended to use itServletRegistrationBeanTo implement Servlet registration and inject dependencies.

Implementation steps:

Define Service Class

@Service
public class MyService {
    public String process() {
        return "Service processing...";
    }
}

Define Servlet class

public class MyServlet extends HttpServlet {

    private final MyService myService;

    public MyServlet(MyService myService) {
         = myService;
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String result = ();
        ().write("Result from service: " + result);
    }
}

Configure Servlet Registration
In the Spring Boot configuration class, register the Servlet:

@Configuration
public class ServletConfig {

    @Bean
    public ServletRegistrationBean<MyServlet> myServletRegistration(MyService myService) {
        return new ServletRegistrationBean<>(new MyServlet(myService), "/myServlet");
    }
}

Run the application
Run the application through Spring Boot startup class:

@SpringBootApplication
public class MyApplication {
    public static void main(String[] args) {
        (, args);
    }
}

Summarize

The above four methods can select suitable solutions based on project requirements and technology stack:

If using@WebServlet, use directly@Autowiredannotation.
If more flexible control is required, you canServletRegistrationBeanRegister a Servlet.
If using traditionalConfiguration, can be usedSpringBeanAutowiringSupportImplement dependency injection.
Recommended use of Spring BootServletRegistrationBeanServlet registration.

In actual development, using Spring Boot can simplify the configuration process and is a preferred solution!

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