如何通过Http连接调用GWT的方法？

import com.google.gwt.user.client.rpc.RemoteService;
import com.google.gwt.user.client.rpc.RemoteServiceRelativePath;

@RemoteServiceRelativePath("gwtService")
public interface GwtService extends RemoteService {
    String performAction(String parameter);
}

import com.google.gwt.user.server.rpc.RemoteServiceServlet;

public class GwtServiceImpl extends RemoteServiceServlet implements GwtService {
    public String performAction(String parameter) {
        // 在这里实现具体的方法逻辑
        return "Result: " + parameter;
    }
}

<servlet>
    <servlet-name>GwtService</servlet-name>
    <servlet-class>com.example.GwtServiceImpl</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>GwtService</servlet-name>
    <url-pattern>/gwtService</url-pattern>
</servlet-mapping>

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.user.client.rpc.ServiceDefTarget;

public class GwtEntryPoint implements EntryPoint {
    public void onModuleLoad() {
        GwtService gwtService = (GwtService) GWT.create(GwtService.class);
        ServiceDefTarget target = (ServiceDefTarget) gwtService;
        String url = GWT.getModuleBaseURL() + "gwtService";
        target.setServiceEntryPoint(url);

        gwtService.performAction("Parameter", new AsyncCallback<String>() {
            public void onSuccess(String result) {
                // 处理成功的回调
                System.out.println(result);
            }

            public void onFailure(Throwable caught) {
                // 处理失败的回调
                caught.printStackTrace();
            }
        });
    }
}