gson 转换时报 NullPointerException

[qq_43270260]

错误信息：
java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at com.ffy.web.servlet.BaseServlet.service(BaseServlet.java:27)
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 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:936)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1135)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
at java.base/java.lang.Thread.run(Thread.java:844)
Caused by: java.lang.NullPointerException
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:96)
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:61)
at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:69)
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:97)
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:61)
at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:69)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:127)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:245)
at com.google.gson.Gson.toJson(Gson.java:704)
at com.google.gson.Gson.toJson(Gson.java:683)
at com.google.gson.Gson.toJson(Gson.java:638)
at com.google.gson.Gson.toJson(Gson.java:618)
at com.ffy.web.servlet.UserServlet.routeList(UserServlet.java:135)
... 22 more

public void getRouteByid (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");

UserService us = new UserService();
String rid = request.getParameter("rid");
Route route = us.getRouteByid(rid);
//商家信息
int sid = route.getSid();
Seller getseller = us.getseller(sid);
route.setSeller(getseller);
//缩略图
int rid1 = route.getRid();
List<RouteImg> routeImgs = us.getrouteImgList(rid1);
route.setRouteImgList(routeImgs);
//商品分类
int cid = route.getCid();
Category getcategory = us.getcategory(cid);
route.setCategory(getcategory);
Gson gson = new Gson();
String s = gson.toJson(route);
response.getWriter().write(s);
}

这里出的错String s = gson.toJson(route);
查了很多一直没有解决，page 有值

[getdate]

实体类里面是否都提供了私有的属性的 的 get set 方法? 可以参考下网上的实例,结合自己的情况看下问题到底出在哪里. https://blog.csdn.net/qq_34292479/article/details/86495412

[qq_43270260]

Caused by: com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: com.ffy.domain.Page["routeList"]->java.util.ArrayList[0]) 集合的空值吗？可是我集合有值呀