GWT - Failed to get type signature for class

Question

I am working on a GWT application that searches for files on different servers. I have a search code in a server package in the Search class. To help find local servers, I have a server location in a class called "Login", which is in a common package. The input contains authentication objects that store information for a separate server.

The code for calling Search is as follows:

SearchInterfaceAsync search = GWT.create(SearchInterface.class); AsyncCallback<Void> callback = new AsyncCallback<Void>() { @Override public void onFailure(Throwable caught) { System.out.println("Error: " + caught.getMessage()); } @Override public void onSuccess (Void results) { System.out.println("Success!"); } }; search.initialize(serverName, login, callback); search.searchServers(search, variousSearchParameters, callback); 

When I run the program and try to search, the program prints Error: could not get type signature for class [Lcom.example.test.shared.Authentication; .

The authentication code is as follows:

 public class Authentication implements Serializable { private static final long serialVersionUID = 5326256122438445301L; private String server; private String userName; private String password; public Authentication(String serverName){ server = serverName; } public Authentication(String serverName, String user, String pass){ server = serverName; userName = user; password = pass; } public String getServer(){ return server; } public String getUserName(){ return userName; } public String getPassword() { return password; } } 

I tried changing the type declaration by adding serialization, switching to IsSerializible, and nothing works!

Answer 1

I tried changing the type declaration by adding serialization, switching to IsSerializible, and nothing works!

You missed one: you must have a default constructor (zero-arg), or a new instance cannot be created. The deserialization process creates an object, then assigns the fields.

I believe that you can protect this constructor so that no developer can accidentally use it.

Answer 2

In case this helps others, these are the reasons for this error that I have encountered recently. Sending objects from client to server:

• Missing constructor no-args public MyObject() {}
• The presence of a member variable defined as Object (an object cannot be serialized)
• Forget to implement Serializable interface
• Using Generics where the type is not defined (I think it was <?> Causing problems).
• Invalid "version" of class "standard" imported. For example, an import List is imported instead of java.util.List.
• The presence of a member variable of type java.io.Serializable. The member variable can migrate the client server in order, but sending back failed. It turned out that the member was wrapped with a GWT class along a path that was not serializable ("ServerSerializationStreamReader $ BoundedList").
• The presence of a sub-object (member variable) with one of the above problems.

These errors in GWT may appear as “500 server errors” that are difficult to debug.

Hope this saves you from cutting your hair.

Answer 3

My problem was the lack of the IsSerializable flag interface in the class indicated in the error.