I was taking a look at WebSockets last week and made a few thoughts on how to implement the server side with the Java Servlet API. I didn't spend too much time, but ran into the following problems during a few tests with Tomcat, which seem impossible to solve without patching the container or at least making container specific modifications to the HttpServletResponse implementation: The WebSocket specification mandate a defined message in the 101 HTTP response. HttpServletResponse.setStatus(int code, String message) is deprecated without mentioning a usable replacement. After changing the default Tomcat configuration, I made Tomcat honor my message string, but since the method is deprecated, I'm not sure if this will work with other servlet containers. The WebSocket specification require a specified order of the first few headers in the HTTP response to the connection upgrade request. The servlet API does not offer a method to specify the order of the response headers and Tomcat adds its own headers to the response, placing a few of them before any headers, which are added by the servlet implementation. Since the content length of the response is not known when committing the header, Tomcat automatically switches to chunked transfer encoding for the response, which is incompatible with the WebSocket specification. Am I missing something obvious, or is it really not possible to integrate WebSocket server endpoints in a servlet based web app?

Reputation: 34313

WebSockets served by a Servlet Container

I was taking a look at WebSockets last week and made a few thoughts on how to implement the server side with the Java Servlet API. I didn't spend too much time, but ran into the following problems during a few tests with Tomcat, which seem impossible to solve without patching the container or at least making container specific modifications to the HttpServletResponse implementation:

The WebSocket specification mandate a defined message in the 101 HTTP response. HttpServletResponse.setStatus(int code, String message) is deprecated without mentioning a usable replacement. After changing the default Tomcat configuration, I made Tomcat honor my message string, but since the method is deprecated, I'm not sure if this will work with other servlet containers.
The WebSocket specification require a specified order of the first few headers in the HTTP response to the connection upgrade request. The servlet API does not offer a method to specify the order of the response headers and Tomcat adds its own headers to the response, placing a few of them before any headers, which are added by the servlet implementation.
Since the content length of the response is not known when committing the header, Tomcat automatically switches to chunked transfer encoding for the response, which is incompatible with the WebSocket specification.

Am I missing something obvious, or is it really not possible to integrate WebSocket server endpoints in a servlet based web app?

Upvotes: 14

Answers (4)

Oliver

Reputation: 11

jWebSocket claims to run as a Tomcat application. Unfortunately some files are missing in the binary distribution of jWebSocket. Some people are trying to recompile jWebSocket and get the necessary files, since the source code is available. All in all, jWebSocket does not seem as a reliable product.

Upvotes: 0