Why can't I get JSON from Struts 2 action?

Question

I want to send Ajax POST request to my Struts action using jQuery like this:

$.ajax({
        type: "POST",
        url: "ds/query",     
        data :JSON.stringify(data),
        dataType:"json",
        contentType: "application/json; charset=utf-8",
        success : function(d, t, x){
            console.log(x);
        }
    });

my action configuaration:

<package name="ds" namespace="/ds" extends="json-default">
        <action name="query" class="gov.cbrc.gzbanking.action.DataServiceAction" method="query">
            <interceptor-ref name="json">
                <param name="enableSMD">true</param>
            </interceptor-ref>
            <result type="json">
                <param name="noCache">true</param>
                <param name="excludeNullProperties">true</param>
                <param name="root">qRes</param>
            </result>
        </action>
    </package>

my action class:

public class DataServiceAction {
    
    private QueryRequest qReq;
    
    private QueryResponse qRes;

    public QueryRequest getQr() {
        return qReq;
    }

    public void setQr(QueryRequest qReq) {
        this.qReq = qReq;
    }
    
    public QueryResponse getqRes() {
        return qRes;
    }

    public void setqRes(QueryResponse qRes) {
        this.qRes = qRes;
    }
    
    public String query() throws Exception{
        App.getLogger().debug(qReq.toString());
        String dsClz = SysCodes.getCodeItem("data_service", qReq.getDs()).getConfig1();
        Class<?> dsCls = Class.forName(dsClz);
        if(!DataService.class.isAssignableFrom(dsCls)){
            throw new Exception("specified class does't implement DataService interface.");
        }else{
            DataService ds = (DataService) dsCls.newInstance();
            System.out.println(JsonUtil.toJson(ds.query(qReq)));
            qRes = ds.query(qReq);
        }
        return ActionSupport.SUCCESS;
    }

}

QueryRequest and QueryResponse are just Java beans, when I execute my code, Server can read JSON data and do its job without error, and I am sure QueryResponse object is popluted with data. but I can't get anything at client side, responseText and responseJson are both null.

Why did not struts2-json-plugin convert my QueryResponse object into JSON string automaticaly?

My QueryResponse class:

public class QueryResponse {
    
    private int total;
    
    private List<?> data;

    public int getTotal() {
        return total;
    }

    public void setTotal(int total) {
        this.total = total;
    }

    public List<?> getData() {
        return data;
    }

    public void setData(List<?> data) {
        this.data = data;
    }
    
    
}

The actual type of data, that the list contains, must be determined at runtime, for example, if data contains list of Role objects:

package gov.cbrc.gzbanking.domain;

public class Role {
 
    private String id;

    private String name;

    private String remark;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

then expected result is like this:

{
total : "1", data :[{"id":"admin", "name":"admin role"}]
}

Answer 1

Because you are using Struts2. Struts2 is used to capitalize property name to resolve a getter method, before a "get" method name could be resolved a property "qRes" capitalized to "QRes" and prefixed with "get". So, the method name will be getQRes. You can remove root parameter from the result and see if it can be used otherwise, or rename a getter method name as

public QueryResponse getQRes() {
    return qRes;
}

You can also read this question about why generated getters and setters in Eclipse don't work with Struts2 OGNL.

Answer 2

I think you are not reading data properly at client side. Try this:

$.ajax({
    type: "POST",
    url: "ds/query",     
    data :JSON.stringify(data),
    dataType:"json",
    contentType: "application/json; charset=utf-8",
    success : function(d, t, x){
        console.log(t);
        console.log(d[0].id);
        console.log(d[0].name);
    }
});