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© 2006-2013 Andrew Cooke (site) / post authors (content).

Forcing lower case HTTP parameter names in Spring

From: andrew cooke <andrew@...>

Date: Sat, 7 Sep 2013 00:49:19 -0400

A client wanted (quite reasonably, imho) the case of REST parameters to be
unimportant.  Unfortunately Spring's RequestParam is case sensitive, and
rewriting the controllers to avoid that would be a fair amount of work.

So, instead, I found that a servlet filter should do the job.  And it works
nicely.

Andrew


In web.xml:

    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>WEB-INF/dispatch-servlet.xml</param-value>
    </context-param>

    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

    <filter>
        <filter-name>delegatingFilter</filter-name>
        <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>delegatingFilter</filter-name>
        <url-pattern>*</url-pattern>
    </filter-mapping>


In dispatch-servlet.xml:

    <bean id="delegatingFilter"
          class="org.springframework.web.filter.DelegatingFilterProxy"
          p:targetBeanName="lowerParams"/>

    <bean id="lowerParams"
          class="com.isti.bss.mvc.LowerCaseParametersFilter"/>


And the code itself:

public final class LowerCaseParametersFilter implements Filter {

    private static final Logger LOG =
            Logger.getLogger(LowerCaseParametersFilter.class);

    @Override
    public void init(final FilterConfig filterConfig) throws ServletException
    {
    }

    @Override
    public void doFilter(final ServletRequest request,
                         final ServletResponse response,
                         final FilterChain chain)
            throws IOException, ServletException {
        if (request instanceof HttpServletRequest) {
            LOG.debug("Wrapping request");
            chain.doFilter(new LowerCaseRequest((HttpServletRequest) request),
                           response);
        } else {
            LOG.warn(format("Not wrapping request: %s", request.getClass()));
            chain.doFilter(request, response);
        }
    }

    @Override
    public void destroy() {
    }

    private static class LowerCaseRequest extends HttpServletRequestWrapper {

        private Map<String, String[]> lowerCaseParams = new HashMap<>();

        public LowerCaseRequest(final HttpServletRequest request) {
            super(request);
            Map<String, String[]> orignalParams = request.getParameterMap();
            for (String name: orignalParams.keySet()) {
                String lower = name.toLowerCase();
                if (!lowerCaseParams.containsKey(lower)) {
                    lowerCaseParams.put(lower, new String[0]);
                }
                lowerCaseParams.put(lower,
                        concat(lowerCaseParams.get(lower),
                                orignalParams.get(name),
                                String.class));
            }
            LOG.debug(lowerCaseParams);
        }

        @Override
        public Map getParameterMap() {
            return new ImmutableMap.Builder<String, String[]>()
                    .putAll(lowerCaseParams).build();
        }

        @Override
        public String getParameter(final String name) {
            String[] values = getParameterValues(name);
            if (values != null) {
                return values[0];
            } else {
                return null;
            }
        }

        @Override
        public Enumeration getParameterNames() {
            return asEnumeration(lowerCaseParams.keySet().iterator());
        }

        @Override
        public String[] getParameterValues(final String name) {
            return lowerCaseParams.get(name);
        }

    }

}

Code Above Contains a BUG!

From: andrew cooke <andrew@...>

Date: Sat, 7 Sep 2013 11:24:48 -0400

There's a subtle but frustrating bug above.  The contextConfigLocation loads
the servelet's context, where everything is defined.  But the delegating
servlet thing also loads that.  In my case, because I was defining schedulers
in the context, I ended up with TWO Quartz schedulers running parallel, and
all tasks being run TWICE.

The solution is simple - separate things into different context files (in my
case I just moved the filter into a completely separate file context file;
more generally you might want ot separate presentation and mid-layer beans).

Andrew

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