Communicating between an HttpServlet and the client side of a GWT application - gwt

I have a simple GWT application that consists of a FormPanel that contains a single FileUpload field. The action on this form is to send it to GWT.getModuleBaseURL() + "process", which web.xml in turn tells GWT is the FileProcessServlet.
FileProcessServlet is a class that I made that extends HttpServlet and overrides doPost(HttpServletRequest req, HttpServletResponse resp) to parse the uploaded file and turn it into a Base64 string using Base64Utils. Now, I would like to pass the client side a single string that is the Base64 encoding of the file just sent it.
For the life of me, I just cannot figure out how to do this. The GWT documentation on Communicating with the Server doesn't say anything about receiving information back from a FormPanel.submit(). There is no callback function associated with such a request, as is the case with GWT RPC. At the same time, I need to use a servlet, since I want to parse a file, and that can't be done by the client. Any suggestions?
~~~~
PS: One option is that I can write directly to the html page from the servlet using java.io's PrintWriter (as this suggests). This may present a kind of solution where I store the Base64 string in a div with a special ID and then use DOM to get this content on the client end. However, I have not yet gotten PrintWriter to cooperate with me. Anytime I use it, with varying content types and character encodings, I still see nothing printed on the page. What I currently have attempting to print this out is:
String base64 = Base64Utils.toBase64(file);
resp.setContentType("text/html; charset=UTF-8");
resp.setCharacterEncoding("UTF-8");
PrintWriter out = resp.getWriter();
out.print(base64);
out.flush(); out.close();
But nothing comes out. The debugger has confirmed that the string base64 is not null nor empty on the penultimate line. Any help on this related front would also be appreciated. Nonetheless, I sincerely hope there is a better way.

form.addSubmitCompleteHandler(new FormPanel.SubmitCompleteHandler() {
public void onSubmitComplete(SubmitCompleteEvent event) {
// When the form submission is successfully completed, this event is
// fired. Assuming the service returned a response of type text/html,
// we can get the result text here (see the FormPanel documentation for
// further explanation).
Window.alert(event.getResults());
}
});
Whatever you write out from the servlet, will be in the event.getResults(), in your case the base64 String

Well I'm not 100% sure if your problem is on client or server side.
For the client:
formPanel.setAction("/[urlMappingOfYourServlet]");
formPanel.setEncoding(FormPanel.[CORRECT_ENCODING]);
formPanel.setMethod(FormPanel.METHOD_POST);
And to start the submission:
formPanel.submit();
Don't forget the mapping of your servlet in your web.xml. E.g.:
<servlet>
<servlet-name>nameOfYourServlet</servlet-name>
<servlet-class>your.package.server.YourServletClass</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>nameOfYourServlet</servlet-name>
<url-pattern>/urlMappingOfYourServlet</url-pattern>
</servlet-mapping>
On the server side you get the parsed data:
String data = request.getParameter("[NameOfYourFormPanelItem]");
You could use a javax.servlet.ServletOutputStream instead of PrintWriter.
ServletOutputStream out = resp.getOutputStream();
out.write(base64);
out.flush();
Another possibility is to use a RequestBuilder on the client side:
RequestBuilder requestBuilder = new RequestBuilder(RequestBuilder.POST, "/urlMappingOfYourServlet");
requestBuilder.sendRequest(someData, new RequestCallback() {
#Override
public void onResponseReceived(Request request,
Response response) {
// ToDo: Get your String here
response.getText();
}
#Override
public void onError(Request request, Throwable exception) {
// ToDo
}
});

Related

gwt getModuleBaseURL on same server creates an java.lang.UnsatisfiedLinkError

I have a single GWT web-application integrated with Spring MVC. I have a working Controller which works perfectly and is unit tested to accept POSTed JSON data and returns JSON data.
From within the same application, to avoid any SOP cross-site domain issues, I am making a call with a RequestBuilder to POST the same json data, and I expect JSON data back.
I created a basic java class that should make a call, but I have a few issues. This running web-app is running in hosted mode in Jetty in Eclipse. I have done a ton of research on how GWT should make a call to an existing web-service with a simple HTP request.
The first issue from my unit test is that:
String baseUrl = GWT.getModuleBaseURL();
is not working and I get:
java.lang.UnsatisfiedLinkError: com.google.gwt.core.client.impl.Impl.getModuleBaseURL()Ljava/lang/String;
I think I know what the correct URL should be, so when I hard-code the url correctly, and execute this code:
String url = getRootUrl() + "rest/pendingInvoices/searchAndCount";
System.out.println("PendingInvoiceDataSource: getData: url=" + url);
// Send request to server and catch any errors.
RequestBuilder builder = new RequestBuilder(RequestBuilder.POST, url);
builder.setHeader("Accept", "application/json");
builder.setHeader("Content-type", "application/json");
// builder.setRequestData(requestData);
try
{
System.out.println("PendingInvoiceDataSource: SEND REQUEST: getData: requestData=" + requestData);
Request request = builder.sendRequest(requestData, new RequestCallback()
{
public void onError(Request request, Throwable exception)
{
System.out.println("Couldn't retrieve JSON");
}
#Override
public void onResponseReceived(Request request, Response response)
{
if (200 == response.getStatusCode())
{
// updateTable(JsonUtils.safeEval(response.getText()));
System.out.println("data=" + response.getText());
}
else
{
System.out.println("Couldn't retrieve JSON (" + response.getStatusText() + ")");
}
}
});
}
catch (RequestException e)
{
System.out.println("Couldn't retrieve JSON");
}
I get this error on he sendRequest:
java.lang.UnsatisfiedLinkError: com.google.gwt.xhr.client.XMLHttpRequest.create()Lcom/google/gwt/xhr/client/XMLHttpRequest;
at com.google.gwt.xhr.client.XMLHttpRequest.create(Native Method)
at com.google.gwt.http.client.RequestBuilder.doSend(RequestBuilder.java:383)
at com.google.gwt.http.client.RequestBuilder.sendRequest(RequestBuilder.java:261)
I think this might be a quick fix, or maybe something small I have forgotten, so I'll try some more testing and see what I can find.
Everything client in GWT is only meant to run on the client-side: compiled to JS or in DevMode.
Only shared, server and vm classes can be used on the server-side.
If you want to get your server URL, use the appropriate methods from the HttpServletRequest (or whatever it is in Spring MVC as it seems from how you tagged the question that's what you're using).
If you want to make HTTP requests from your server, use an HttpURLConnection, or OkHttp, Apache Http Components or similar libraries, or even Spring's own HTTP client API.
Actually, it was only the Unit Test that was having a problem. Once I actually tried to run the deployed code, it all worked. I'll still try h GWTTestCase as suggested in order to get the unit test working.
But everything worked correctly when I ran the deployed code.
I also changed: String baseUrl = GWT.getModuleBaseURL();
which gave me:
http://localhost:8888/MyProject
To: String baseUrl = GWT.getHostPageBaseURL();
which gave me:
http://localhost:8888/
and that all worked.

Local request context in GWT

In Java, there is ThreadLocal, which can be used to carry some data from one object to another without explicit passing as method argument.
I need to intercept GWT request and extract custom HTTP header from it, then I need to store the header value somehow to be processed later.
The problem is that the place to extract the header belongs to RequestBuilder, and there is no way (?) to pass the variable from within RequestBuilder to the custom code actually handling the request/response from server. And it is not possible to pass some variable from client code to that request builder.
ThreadLocal could be the solution, however it is not available in GWT. Is there something I can use?
You can use RequestBuilder.setHeader to set header values for your HTTP request.
On the backend you can use HttpServletRequest of your servlet to retrieve the header values from your HTTP request.
Update:
Some class with a static instance variable:
public class SomeClass {
public static String myVar;
}
And in the RequestBuilder code you can do following:
RequestBuilder request = new RequestBuilder(url);
request.setCallback(new RequestCallback() {
#Override
public void onResponseReceived(Request request, Response response) {
SomeClass.myVar = response.getHeader("someheader");
}
});

GWT JSONPRequestBuilder - "Unknown Token :" error in browser console with Timeout exception at the end

I am trying to call a Restful WS from GWT using JSOPRequestBuilder. I have a similar issue which was reported in the link
http://groups.google.com/group/google-web-toolkit/browse_thread/thread/ef93383aca7a3dfc/d4dc5bad1a9110ea
But, I could not figure out the solution. Kindly help me at the earliest.
My JAX-WS resource code snippet from server
#GET
#Produces(MediaType.APPLICATION_JSON)
public DealerAddress getDealerAddress(#QueryParam("dealerId") String sDealerId) {
DealerAddress dlrAd = new DealerAddress("test", "test", "test", "test", 10, new Date(), new Date());
return dlrAd;
}
Jersey returns a JSON object of DealerAddress.
Now rest URL "https://127.0.0.1:8181/application/rest/OrderManagementResource?alt=json-in-script&dealerId=DLR1"
works absolutely fine when i tried request in browser.
It even works with RequestBuilder approach from GWT but not with JSONPRequestBuilder approach.
Code snippet to invoke WS from GWT using JSONPRequestBuilder
JsonpRequestBuilder jsonPReqBuilder = new JsonpRequestBuilder();
jsonPReqBuilder.setTimeout(100000);
jsonPReqBuilder.setCallbackParam("callback");
jsonPReqBuilder.requestObject("https://127.0.0.1:8181/application/rest/OrderManagementResource?alt=json-in-script&dealerId=DLR1" , new AsyncCallback<DealerAddressJSON>() {
#Override
public void onFailure(Throwable caught) {
// TODO Auto-generated method stub
caught.printStackTrace();
Window.alert("Inside error"+caught.getLocalizedMessage());
}
#Override
public void onSuccess(DealerAddressJSON result) {
// TODO Auto-generated method stub
Window.alert("Inside success"+result);
}
});
where as DealerAddressJSON is a JavaScriptObject type class.
I could see that my JAX Rest resource getting called and saying returning from server.
Also, I could see that in Firebug that the response comes in browser but fails with an exception "Unknown token :"
At the end I always get a Timeout exception.
Now I am in big question whether the way we return JSON from JAX-RS resource is a problem in server
or
JSONPRequestBuilder calling procedure is a problem? I could not understand the callback changes which some of the links explained on this issue.
Kindly help me.
You are probably sending back JSON, while the JSONPRequestBuilder expects JSONP. These are not the same thing.
JSON is just the data, as is - make the request using AJAX (i.e. the RequestBuilder), and the contents can be read directly. These requests can only be made to the same server. Example JSON data:
{"response":"success", "items":[{"id":1}, {"id":2}]}
In contrast, JSONP is designed for cross-origin requests, so instead of just containing the data, the data is wrapped up in a JavaScript. Since your JSON service isn't wrapping the a response in a js function call, this isn't working. Example JSONP data:
callback_1({"response":"success", "items":[{"id":1}, {"id":2}]})
The callback changes with each request, so the server is supposed to change that callback function based on what the client requested each time.

In GWT, when is the AsyncCallback:onFailure method called in a json-p request using JsonpRequestBuilder

I've been implementing a GWT application that calls a REST-service (which we're also developing). When the REST-service returns anything with a HTTP-status other than 200 I would expect the onFailure method of AsyncCallback to be called. However I can't get this to happen.
To test it further I created a test GWT app and a test servlet. The part of the GWT app that calls the service looks like this:
JsonpRequestBuilder jsonp = new JsonpRequestBuilder();
jsonp.setCallbackParam("_jsonp");
jsonp.setFailureCallbackParam("_jsonp_failure");
jsonp.requestObject(url, new AsyncCallback<JavaScriptObject>()
{
#Override
public void onFailure(Throwable caught)
{
Window.alert("Failure: " + caught.getMessage());
}
#Override
public void onSuccess(JavaScriptObject result)
{
Window.alert("Success");
}
});
The servlet-code looks like this:
public class MyRestServlet extends HttpServlet
{
protected void doGet(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws ServletException, IOException
{
String padding = httpServletRequest.getParameter("_jsonp_failure");
httpServletResponse.setContentType("application/x+javascript");
httpServletResponse.setStatus(500);
PrintWriter out = httpServletResponse.getWriter();
out.println(padding + "({\"some\":\"json\"});");
out.close();
}
}
OnFailure eventually gets called when the request times out, but I would expect it to be called as soon as the http response arrives(if it's a failure). I guess there is something I haven't understood and I would really appreciate to get some help with this.
Thanks
According to HTML5, if there's an error loading the script, an error event should be dispatched, and GWT doesn't listen for it (because almost no browser actually fires it AFAICT).
For best browser compatibility, you'd better always send a 200 status, but then call the failure callback (or in other words, return an error state/condition, rather than throw an exception).
Also, the argument to the failure callback is expected to be a string (will be the message of the exception).
From the server code where you call the REST service, throw an exception yourself if the response is something other than 200 (by writing code to check the response yourself). This way it will persist to the client side as an error and onFailure will be called in client side.
In GWT's mind currently nothing went wrong. It sent a request, got some result did not matter what, the call was successful. It does call the onFailure on a timeout because something did go wrong with the request "physically", and GWT persisted the exception to the client side as a failure.

How to fix Jersey POST request parameters warning?

I'm building a very simple REST API using Jersey, and I've got a warning in my log files that I'm not sure about.
WARNING: A servlet POST request, to
the URI
http://myserver/mycontext/myapi/users/12345?action=delete,
contains form parameters in the
request body but the request body has
been consumed by the servlet or a
servlet filter accessing the request
parameters. Only resource methods
using #FormParam will work as
expected. Resource methods consuming
the request body by other means will
not work as expected.
My webapp only has the Jersey servlet defined, mapped to /myapi/*
How can I stop these warnings?
For me the warning was showing for POST application/x-www-form-urlencoded. And I am using Spring Boot which has an HiddenHttpMethodFilter that does a getParameter before anything else... So I ended up doing this nasty override:
#Bean
public HiddenHttpMethodFilter hiddenHttpMethodFilter() {
return new HiddenHttpMethodFilter() {
#Override
protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,
FilterChain filterChain) throws ServletException, IOException {
if ("POST".equals(request.getMethod())
&& request.getContentType().equals(MediaType.APPLICATION_FORM_URLENCODED_VALUE)) {
filterChain.doFilter(request, response);
} else {
super.doFilterInternal(request, response, filterChain);
}
}
};
}
This message is meant to warn developers about the fact that the request entity body has been consumed, thus any other attempts to read the message body will fail.
It is safe to ignore the message or filter it out from the logs:
java.util.logging.Logger jerseyLogger =
java.util.logging.Logger.getLogger(WebComponent.class.getName());
jerseyLogger.setFilter(new Filter() {
#Override
public boolean isLoggable(LogRecord record) {
boolean isLoggable = true;
if (record.getMessage().contains("Only resource methods using #FormParam")) {
isLoggable = false;
}
return isLoggable;
}
});
The following thread describes the warning you are receiving. It sounds as though you might have a filter defined in your web.xml that is processing the request before Jersey does.
Finally got rid of this by making sure I had Content-Type: application/json in my request headers (obviously, on the client side)
I just had my ajax-function in JQuery set to contentType: "application/x-www-form-urlencoded; charset=UTF-8" because with a prior solution (without Jersey) I had some encoding problems. When I removed that the message was gone and everything worked fine.
This warning is the only thing the WebComponent logs, so just turn logging up to ERROR level or turn off logging for this component in your logback.xml or wherever you have logging configured. You don't need to write a custom filter to ignore this specific message since there are no other messages logged from this component.
Source code snippet from org.glassfish.jersey.servlet.WebComponent version 2.14:
if(!form.asMap().isEmpty()) {
containerRequest.setProperty("jersey.config.server.representation.decoded.form", form);
if(LOGGER.isLoggable(Level.WARNING)) {
LOGGER.log(Level.WARNING, LocalizationMessages.FORM_PARAM_CONSUMED(containerRequest.getRequestUri()));
}
}
The localized message that is used for this warning message is:
form.param.consumed=A servlet request to the URI {0} contains form parameters in the request body but the request body has been consumed by the servlet or a servlet filter accessing the request parameters. Only resource methods using #FormParam will work as expected. Resource methods consuming the request body by other means will not work as expected.
Turn logging off for the WebComponent in your logback.xml like so:
<logger name="org.glassfish.jersey.servlet.WebComponent" level="OFF" additivity="false"/>
Right.
So I've been suffering this issue, and I've been trying to solve it on different ways, but I did't want to change my web.xml settings, just because if I was testing my application with Postman it worked perfect, but when it was being integrated with the webapp it fails with the mentioned issue (A servlet request to the URI {MY_URI} contains form parameters in the request body but the request body has been consumed by the servlet or a servlet filter accessing the request parameters. Only resource methods using #FormParam will work as expected. Resource methods consuming the request body by other means will not work as expected.)
So as #clijk mentioned, you only have to set your headers as:
"Content-Type":"application/json"
"charset":"UTF-8"
and voilá, the warning it's gone.
Thanks
In my case I've fixed this error when I've changed the Object Date to String in the method.
Error:
#POST
#Path("/myPath")
#Produces(MediaType.APPLICATION_JSON)
public List<MyObject> myMethod(#FormParam("StartDate") Date date) throws Exception {
Fixed
#POST
#Path("/myPath")
#Produces(MediaType.APPLICATION_JSON)
public List<MyObject> myMethod(#FormParam("StartDate") String date) throws Exception {
Put this to your resource signature. Or find this string in your project someone already use this if #PUT or #POST is used. This should help
import javax.ws.rs.Consumes;
#Consumes(MediaType.APPLICATION_JSON)