How to inject service in servlet

Spring's mvc framework is used at work, which is divided into three levels: controller/service/dao. Occasionally, a servlet is used to replace the controller, and this is how to use a service bean injected into the spring context in a servlet.

By querying relevant information, you can call spring's method in the servlet's initialization method for injection

 

@Override
    public void init(ServletConfig config) throws ServletException
    {
        SpringBeanAutowiringSupport.processInjectionBasedOnServletContext(this, config.getServletContext());
    }

 

At the same time, the field corresponding to the type instance to be injected needs to be added to the current servlet, as shown below

@Autowired
     private TestAppService testAppService;

=========================================
Example in the project:

public class WeixinServlet1 extends HttpServlet {
     @Override
    public void init(ServletConfig config) throws ServletException { SpringBeanAutowiringSupport.processInjectionBasedOnServletContext(this, config.getServletContext()); } @Autowired private GoodService goodService; ......

Without the init method, just injecting the service will report an error:

严重: Servlet.service() for servlet [WeixinServlet] in context with path [/weixin] threw exception
java.lang.NullPointerException
    at com.test.www.servlet.WeixinServlet1.doPost(WeixinServlet1.java:127)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at com.alibaba.druid.support.http.WebStatFilter.doFilter(WebStatFilter.java:124)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:85)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:947)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1009)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:748)

With the init method it is normal.