servlet中怎么注入service

在工作中使用到spring的mvc框架，分为controller/service/dao三个层次。偶尔会用到servlet替换掉controller，这就遇到如何在servlet中使用注入到spring上下文中的service bean。

通过查询相关资料，可以在servlet的初始化方法中调用spring的方法进行注入

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

同时需要在当前的servlet中加上需要注入的类型实例对应的字段,如下所示

@Autowired
    private TestAppService testAppService;

======================================
项目中示例：

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

        ......

注意：

不加init方法只是注入service是会报错：

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)

加上init方法就正常了。

注入service使用@Resource会报错：

严重: Allocate exception for servlet WeixinServlet
javax.naming.NamingException: Cannot create resource instance
    at org.apache.naming.factory.ResourceEnvFactory.getObjectInstance(ResourceEnvFactory.java:117)
    at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:321)
    at org.apache.naming.NamingContext.lookup(NamingContext.java:843)
    at org.apache.naming.NamingContext.lookup(NamingContext.java:154)
    at org.apache.naming.NamingContext.lookup(NamingContext.java:831)
    at org.apache.naming.NamingContext.lookup(NamingContext.java:168)
    at org.apache.catalina.core.DefaultInstanceManager.lookupFieldResource(DefaultInstanceManager.java:580)
    at org.apache.catalina.core.DefaultInstanceManager.processAnnotations(DefaultInstanceManager.java:470)
    at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:157)
    at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:138)
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1144)
    at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:865)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:136)
    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)

使用@Autowired就正常了。