I have a class looking like this:
class MyClass {
public int Id;
public Dictionary<int, MyClass[]> ChildValues;
}
when I try to deserialize this class using Json.NET:
MyClass x = return JsonConvert.DeserializeObject<MyClass>(s);
I receive the error Expected a JsonObjectContract or JsonDictionaryContract for type 'System.Collections.Generic.Dictionary`2[System.Int32,MyClass[]]', got 'Newtonsoft.Json.Serialization.JsonDictionaryContract'.
What does this error message mean and how can I resolve it?
Take a look at JSON you have in s variable first.
I found it. The problem was that the Json from the client was an array and not a dictionary (which in turn was because the script file was cached by IE).
Related
I'm using Spring 3.1 and I have a handler that should return a String value.
Here's how my handler looks like:
#RequestMapping(value = TEST_HANDLER_PATH, method = RequestMethod.POST)
public ResponseEntity<String> handleTest(HttpServletRequest request,
#RequestParam("parma1") String param) throws Exception {
String ret = ...
...
HttpHeaders headers = new HttpHeaders();
headers.add("Content-Type", "text/plain;charset=utf-8");
return new ResponseEntity<String>(ret, headers, HttpStatus.CREATED);
}
I also tried annotating method with #ResponseBody with return ret; at the end.
In both cases, when I hit the service, I get extra quotes around String value (e.g. "This is a test").
I'm guessing this is due to message conversion. That's why I tried defining Content-Type header, to hit StringHttpMessageConverter explicitly, to no avail.
Had the same problem.
Just make sure you register a org.springframework.http.converter.StringHttpMessageConverter as well as your Jackson one so that Strings are treated literally and not attempted to be converted to JSON (with extra quotes).
Just instantiate with default constructor or constructor with your preferred Charset. The media types should be set for you with the standard internal defaults. If you're configuring via code extending WebMvcConfigurerAdapter then you just add the converters in the configureMessageConverters(List<HttpMessageConverter<?>> converters) method.
In my case, I had over-engineered =)
Had introduced a converter for bean's toString Operations like this:
class SerializableToString implements Converter<Serializable, String>
restricting that (only to my beans), resolved the issue X)
Note: debugging with a breakpoint # org.springframework.core.convert.support.GenericConversionService.getConverter helped.
In a related scenario, I had an IntegrationFlow for a GET that incorrectly requested a transform. Basically the target service would receive the #PathVariable as a quote escaped string
return IntegrationFlows.from("getThing")
.transform(Transformers.toJson())
.handle(
The .transform(Transformers.toJson()) was forcing the strings to be escaped in the URI, so simply removing it - it shouldn't have been there - fixed the issue.
Turns out there was a JSON message converter registered in one of the imports.
I am trying to avoid some naming conflicts in my uploaded files (I used com.oreilly.servlet.MultipartRequest ).
At this moment my constructor looks like this:
MultipartRequest multi = new MultipartRequest(request, uploadPath);
I would like to implement the constructor with FileRenamePolicy in order to rename my file with a value taken from a form (something like request.getParameterValue("title");
I think I should use the foloowing constructor? But I don't know how to set the "policy" paramter
MultipartRequest(javax.servlet.http.HttpServletRequest request,
java.lang.String saveDirectory,
int maxPostSize,
java.lang.String encoding,
FileRenamePolicy policy)
Do you have any suggestions?
Thanks!
You should implement a custom FileRenamePolicy which gives you the File appending the title sent along with the request.
Here is what you are looking for:
private static class MyTitleRenamePolicy extends FileRenamePolicy {
java.io.File rename(java.io.File f) {
return new File(f.getParentFile(),
rename.getName() + "_"+ request.getParameter("title"));
}
}
new MultipartRequest(request, saveDirectory, maxPostSize, encoding,
new MyTitleRenamePolicy(request));
I have the following web service:
[ScriptService]
public class Handler : WebService {
[WebMethod]
public void method1() {
string json = "{ \"success\": true }";
System.Web.HttpContext.Current.Response.Write(json);
}
[WebMethod]
public object method2(Dictionary<string, object> d) {
Dictionary<string, object> response = new Dictionary<string, object>();
response.Add("success", true);
return response;
}
}
The first method accepts a traditional html form post and response writes a JSON string to the page. The second method accepts a JSON value posted via AJAX and returns a serialized object.
Both these methods work fine on their own but when put together in the same web service I get this error when calling method1:
System.IndexOutOfRangeException: Index was outside the bounds of the array.
When I remove the arguments from method2 they work.
Can anyone suggest why this is happening?
Edit:
The problem spans from the argument type of method2. If I change it to a string or simple data type it works fine. As Joel suggests it's probably because Dictionaries can't be serialized. This doesn't seem to affect my requests sent by ajax and only breaks direct form posts to this handler. Therefore my workaround is to put the form post handlers in a separate file by themselves. Not ideal but works for my application.
Dictionaries are not serializable. Hiding it behind an object doesn't do anything for you. You must first convert your dictionary to an array or some other serializable object before sending it out.
Why isn't there an XML-serializable dictionary in .NET?
http://weblogs.asp.net/pwelter34/archive/2006/05/03/444961.aspx
http://www.tanguay.info/web/index.php?pg=codeExamples&id=333
I've just found a strange error when deserializing from a ByteArray, where Vectors cannot contain types that extend Array: there is a TypeError when they are deserialized.
TypeError: Error #1034: Type Coercion failed: cannot convert []#4b8c42e1 to com.myapp.ArraySubclass.
at flash.utils::ByteArray/readObject()
at com.myapp::MyApplication()[/Users/aaaidan/MyApp/com/myapp/MyApplication.as:99]
Here's how:
public class Application extends Sprite {
public function Application() {
// register the custom class
registerClassAlias("MyArraySubclass", MyArraySubclass);
// write a vector containing an array subclass to a byte array
var vec:Vector.<MyArraySubclass> = new Vector.<MyArraySubclass>();
var arraySubclass:MyArraySubclass = new MyArraySubclass();
arraySubclass.customProperty = "foo";
vec.push(arraySubclass);
var ba:ByteArray = new ByteArray();
ba.writeObject(arraySubclass);
ba.position = 0;
// read it back
var arraySubclass2:MyArraySubclass = ba.readObject() as MyArraySubclass; // throws TypeError
}
}
public class MyArraySubclass extends Array {
public var customProperty:String = "default";
}
It's a pretty specific case, but it seems very odd to me. Anyone have any ideas what's causing it, or how it could be fixed?
well, it seems array serialization is hardcoded. you should definitely post a bug report.
actually the code you posted doesn't throw an error since ba.readObject() as MyArraySubclass is simply null. MyArraySubclass(ba.readObject()) however would.
what you could try to fix it, would be to implement IExternalizable, altough I'm not sure it'll work any better.
I guess the problem is that Array is a very very special class in ActionScript (in the sense that in some way it is nothing more than any other dynamic class, but in other ways it's not at all) which leads to a lot of Array-specific code in the VM. Also, a question is, why do you need to subclass Array?
Pardon me if this question has already been asked. HttpContext.Current.Session["key"] returns an object and we would have to cast it to that particular Type before we could use it. I was looking at various implementations of typed sessions
http://www.codeproject.com/KB/aspnet/typedsessionstate.aspx
http://weblogs.asp.net/cstewart/archive/2008/01/09/strongly-typed-session-in-asp-net.aspx
http://geekswithblogs.net/dlussier/archive/2007/12/24/117961.aspx
and I felt that we needed to add some more code (correct me if I was wrong) to the SessionManager if we wanted to add a new Type of object into session, either as a method or as a separate wrapper. I thought we could use generics
public static class SessionManager<T> where T:class
{
public void SetSession(string key,object objToStore)
{
HttpContext.Current.Session[key] = objToStore;
}
public T GetSession(string key)
{
return HttpContext.Current.Session[key] as T;
}
}
Is there any inherent advantage in
using
SessionManager<ClassType>.GetSession("sessionString")
than using
HttpContext.Current.Session["sessionString"] as ClassType
I was also thinking it would be nice
to have something like
SessionManager["sessionString"] = objToStoreInSession,
but found that a static class cannot have an indexer. Is there any other way to achieve this ?
My thought was create a SessionObject which would store the Type and the object, then add this object to Session (using a SessionManager), with the key. When retrieving, cast all objects to SessionObject ,get the type (say t) and the Object (say obj) and cast obj as t and return it.
public class SessionObject { public Type type {get;set;} public Object obj{get;set;} }
this would not work as well (as the return signature would be the same, but the return types will be different).
Is there any other elegant way of saving/retrieving objects in session in a more type safe way
For a very clean, maintainable, and slick way of dealing with Session, look at this post. You'll be surprised how simple it can be.
A downside of the technique is that consuming code needs to be aware of what keys to use for storage and retrieval. This can be error prone, as the key needs to be exactly correct, or else you risk storing in the wrong place, or getting a null value back.
I actually use the strong-typed variation, since I know what I need to have in the session, and can thus set up the wrapping class to suit. I've rather have the extra code in the session class, and not have to worry about the key strings anywhere else.
You can simply use a singleton pattern for your session object. That way you can model your entire session from a single composite structure object. This post refers to what I'm talking about and discusses the Session object as a weakly typed object: http://allthingscs.blogspot.com/2011/03/documenting-software-architectural.html
Actually, if you were looking to type objects, place the type at the method level like:
public T GetValue<T>(string sessionKey)
{
}
Class level is more if you have the same object in session, but session can expand to multiple types. I don't know that I would worry about controlling the session; I would just let it do what it's done for a while, and simply provide a means to extract and save information in a more strongly-typed fashion (at least to the consumer).
Yes, indexes wouldn't work; you could create it as an instance instead, and make it static by:
public class SessionManager
{
private static SessionManager _instance = null;
public static SessionManager Create()
{
if (_instance != null)
return _instance;
//Should use a lock when creating the instance
//create object for _instance
return _instance;
}
public object this[string key] { get { .. } }
}
And so this is the static factory implementation, but it also maintains a single point of contact via a static reference to the session manager class internally. Each method in sessionmanager could wrap the existing ASP.NET session, or use your own internal storage.
I posted a solution on the StackOverflow question is it a good idea to create an enum for the key names of session values?
I think it is really slick and contains very little code to make it happen. It needs .NET 4.5 to be the slickest, but is still possible with older versions.
It allows:
int myInt = SessionVars.MyInt;
SessionVars.MyInt = 3;
to work exactly like:
int myInt = (int)Session["MyInt"];
Session["MyInt"] = 3;