return JSON message from struts2 action

I use jquery and struts2 in my web application. Now I need to开发者_开发问答 embed a google map into my web page and add some marker. I use jquery.getJSON() command to send request to struts2 action.

In the struts.xml

<package name="ajax" namespace="/ajax" extends="json-default">
    <action name="LatLngList" class="com.test.ajax.Action" method="find">
        <result type="json"></result>
    </action>
</package>

In the web page

<script type="text/javascript">
    function readLatLng() { 
        var latitude = new Array();
        var longitude = new Array();
        $.getJSON("ajax/LatLngList.action?id=9", function(data){
            $.each(data, function(i,latlng){
            latitude.push(latlng.latitude);
            longitude.push(latlng.longitude);       
            });
        });
    }
</script>

In the action, I read data from database and create a list of object and then use jackson json processor's ObjectMapper to convert the List to JSON String. Finally, I return the JSON String as return value.

public String find() throws JsonGenerationException, JsonMappingException, IOException {

    List latlngList = new ArrayList();
    /*
    latlngList.add(...);
    */

    ObjectMapper mapper = new ObjectMapper();
    String str = mapper.writeValueAsString(latlngList);
    System.out.println(str);
    return str;
}

When I run the web application, the JSON String show in the console:

[
{"latitude":37.7935697,"longitude":121.181969},

{"latitude":37.7852119,"longitude":121.1759833},

{"latitude":37.7858117,"longitude":121.1250904},

{"latitude":37.794129,"longitude":121.1229535},

{"latitude":37.7974078,"longitude":121.0874301},

{"latitude":37.8280231,"longitude":121.049312}
]

However, It give me the error.

No result defined for action com.test.ajax.Action and result [{"latitude":37.7935697,"longitude":121.181969},{"latitude":37.7852119,"longitude":121.1759833},{"latitude":37.7858117,"longitude":121.1250904},{"latitude":37.794129,"longitude":121.1229535},{"latitude":37.7974078,"longitude":121.0874301},{"latitude":37.8280231,"longitude":121.049312}]
    at com.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:375)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:277)
    at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:176)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:263)
    at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:133)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:190)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:243)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:270)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:176)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:190)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
    at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:498)
    at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
    at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)
    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:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:291)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:680)

I have search for a long time but still cannot find out the solution. Waiting for your help. Thank you very much.

It's been a long time since I used Struts2, but from memory you don't return your response from the action, you return a simple string name that determines which result in the config to use, then the properties on the controller class become available to your view. When returning a json result these properties are serialized for you into JSON to be returned.

So you want something more like this:

private List latlngList;
public List getLatLngList() {
    return latlngList;
}

public String find() throws JsonGenerationException, JsonMappingException, IOException {
    latlngList = new ArrayList()
    /*
    latlngList.add(...);
    */

    return "success";
}

And then in your javascript grab the LatLngList property of the resulting JSON (note the change from data to data.latLngList):

<script type="text/javascript">
    function readLatLng() { 
        var latitude = new Array();
        var longitude = new Array();
        $.getJSON("ajax/LatLngList.action?id=9", function(data){
            $.each(data.latLngList, function(i,latlng){
                latitude.push(latlng.latitude);
                longitude.push(latlng.longitude);       
            });
        });
    }
</script>

Because you're doing a mix between looking like you're using the JSON plugin, and directly rendering the result. Meaning neither will work. Actions return the name of a result, not raw data. (Or rather they can return raw data, but then must be handled differently.)

Check out the documentation for the JSON plugin.