问题背景：从前端传来的json字符串中取某些值，拼接成json格式入参调外部接口。
报如下错：
java.lang.ClassCastException: java.util.HashMap cannot be cast to java.lang.String
at com.taobao.hsf.proxy.bytecode.proxy31.registerCancellation(proxy31.java)
at com.ohaotian.approval.controller.spzx.TestSgByPiovtController.testFG(TestSgByPiovtController.java:69)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at com.thetransactioncompany.cors.CORSFilter.doFilter(CORSFilter.java:198)
at com.thetransactioncompany.cors.CORSFilter.doFilter(CORSFilter.java:244)
at com.ohaotian.plugin.security.filter.Filter0_CrossOriginResource.doFilter(Filter0_CrossOriginResource.java:41)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.springframework.session.web.http.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:74)
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:347)
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:263)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:208)
at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:177)
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:347)
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:263)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.springframework.session.web.http.SessionRepositoryFilter.doFilterInternal(SessionRepositoryFilter.java:167)
at org.springframework.session.web.http.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:80)
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:347)
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:263)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1080)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:314)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
原因分析：
没有取得到 bdcqzh的值 。导致拼接时空。传入接口时解析出错，取值时，可能出现转换异常。
//方法入参，前端传进字符串的json对象
JSONObject jsonObject = JSON.parseObject(formInfos);
//取值 ：
String bdcqzh = jsonObject.getString("CQZH");
//拼接：
jsonReq.put("bdcqzh", bdcqzh);
//调外部接口：
jsonRsp = xxxxService.queryxxxxx(jsonReq);
解决方法：
调接口时加一个if语句判断是否为空
if (bdcqzh != null && !"".equals(bdcqzh)) {
//接口
}
