用純Servlet實現一個REST“框架”，就這么簡單

/**


REST請求分派器
/
@WebServlet(name = "Dispatcher", urlPatterns = "/rest/")
public class Dispatcher extends HttpServlet {
 /**

URL與請求處理器的映射
*/
private Map<Pattern, Class> handlers = new HashMap<Pattern, Class>() {{
 put(Pattern.compile("^/devices/([^/]+)$"), DeviceHandler.class);
}};
@Override
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 try {

 boolean matched = false;
 String path = request.getPathInfo();
 for (Pattern pattern : handlers.keySet()) {
     Matcher matcher = pattern.matcher(path);
     if (matcher.lookingAt()) {
         int groupCount = matcher.groupCount();
         String[] args = new String[groupCount];
         if (groupCount > 0) {
             for (int i = 0; i < matcher.groupCount(); i++) {
                 args[i] = matcher.group(i + 1);
             }
         }
         Class handlerClass = handlers.get(pattern);
         Object handlerInstance = handlerClass.newInstance();
         handlerClass.getField("request").set(handlerInstance, request);
         handlerClass.getField("response").set(handlerInstance, response);
         handlerClass.getMethod(request.getMethod().toLowerCase(), String[].class).invoke(
                 handlerInstance,
                 (Object) args
         );
         matched = true;
         break;
     }
 }
 if (!matched) {
     throw new Exception(String.format("No handler found to deal with path \"%s\"", path));
 }

} catch (Exception ex) {

 response.setStatus(500);
 response.setContentType("text/plain;charset=UTF-8");
 PrintWriter out = response.getWriter();
 ex.printStackTrace(out);
 out.flush();
 out.close();

}
}
}</pre> 
 


/**




REST請求處理器
*/
public abstract class Handler {
 public HttpServletRequest request;
 public HttpServletResponse response;
public void get(String[] args) throws Exception {

 throw new Exception("Not implemented");

}
public void post(String[] args) throws Exception {

 throw new Exception("Not implemented");

}
public void put(String[] args) throws Exception {

 throw new Exception("Not implemented");

}
public void delete(String[] args) throws Exception {

 throw new Exception("Not implemented");

}
public void writeJsonObject(Object object) throws Exception {

 response.setContentType("application/json;charset=UTF-8");
 PrintWriter out = response.getWriter();
 out.println(Json.dump(object));
 out.flush();
 out.close();

}
}</pre> 
 


/*
*/
public class DeviceHandler extends Handler {
 @Override
 public void get(String[] args) throws Exception {


 Map ret = new HashMap();
 List result = Db.query("select id, name, description from devices");
 for (Object record : result) {
     Object id = ((Map) record).get("id");
     Map device;
     if (!ret.containsKey(id)) {
         device = new HashMap();
         ret.put(id, device);
     } else {
         device = (Map) ret.get(id);
     }
     device.put("name", ((Map) record).get("name"));
     device.put("description", ((Map) record).get("description"));
 }
 writeJsonObject(ret);

}
}</pre>