【spring 注解 错误】使用controller 作为后台给前台ajax交互数据出错

controller作为后台与前台的ajax进行交互，后台的方法处理完成返回一个boolean类型的值，想传给前台用来判断是否执行成功，BUT，问题来了：

 严重: Servlet.service() for servlet rest threw exception
 java.lang.IllegalArgumentException: Unknown return value type [java.lang.Boolean]
     at org.springframework.util.Assert.notNull(Assert.java:112)
     at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:70)
     at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:126)
     at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:777)
     at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:706)
     at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
     at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
     at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
     at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
     at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:868)
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:643)
     at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
     at com.agen.util.LoginFilter.doFilter(LoginFilter.java:58)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
     at org.springframework.orm.hibernate4.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:150)
     at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
     at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
     at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
     at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
     at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
     at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
     at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
     at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
     at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
     at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:879)
     at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:617)
     at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1778)
     at java.lang.Thread.run(Unknown Source)

此刻的controller的代码是这样的：

 @RequestMapping("/productAdd")

     public boolean productAdd(Product product){
         product.setProductId(UUID.randomUUID().toString());
         Criteria criteria  = getCurrentSession().createCriteria(Product.class);
         criteria.setProjection(Projections.max("productOrder"));
         Integer productOrder2 = productService.uniqueResultInt(criteria);
         Integer procuctOrder=1;
         if(productOrder2 == null){
             product.setProductOrder(procuctOrder);
         }else{
             productOrder2++;
             product.setProductOrder(productOrder2);
         }
         productService.save(product);
         return true;
     }

问题：

此刻的controller只能识别返回的true作为字符串，也就是URL去找对应的页面，但是哪里有URL是这样的。

分析问题：

而且我们是想把这个true作为返回值给前台的ajax来判断的，如果为true则插入成功给个提示等等，所以我们不想让这个true作为URL去返回，而是作为JSON格式的数据返回给前台

解决方法：

我们需要给这个方法上加一个 spring的注解，让方法返回一个json数据给前台   这个注解就是：@ResponseBody

 @RequestMapping("/productAdd")
     @ResponseBody
     public boolean productAdd(Product product){
         product.setProductId(UUID.randomUUID().toString());
         Criteria criteria  = getCurrentSession().createCriteria(Product.class);
         criteria.setProjection(Projections.max("productOrder"));
         Integer productOrder2 = productService.uniqueResultInt(criteria);
         Integer procuctOrder=1;
         if(productOrder2 == null){
             product.setProductOrder(procuctOrder);
         }else{
             productOrder2++;
             product.setProductOrder(productOrder2);
         }
         productService.save(product);
         return true;
     }

如此 就可以将true作为JSON数据返回给前台了