Java Url Rewrite Tool : UrlRewriteFilter

Url rewrite is a common requirement in the web development. Apache Web Server uses its module mod_rewrite to offere a powerful Url rewrite function. In this post, i make some introduction to UrlRewriteFilter which is a very powerful tool just like Apache's mod_rewrite.

Here is the detailed manul UrlRewriteFilter. It is east to use in your Java web project following the steps. It is also apparently that UrlRewriteFilter takes great advantage of Java Servlet's filter. In the following recipe, i want to highligh the java annotation implementation.

UrlRewriteFilter provides three kinds of annotations: @HttpUrl , @HttpParam @HttpJson

@Retention(RetentionPolicy.SOURCE)@Target(ElementType.METHOD)public @interface HttpUrl {    String value();    /**     * A weighting to be applied to the url, if higher it will move this url to the "top" if lower more towards the     * "bottom".     *     * @return weight     */    int weight() default 0;}

@Retention(RetentionPolicy.SOURCE)@Target(ElementType.PARAMETER)public @interface HttpParam {    /**     * If not set will use the name of the parameter (case insensitive).     * can be a expression ie, $1 (the first group of @HttpUrl regexp), %{header:user-agent} (the user agent header).     *     * @return value     */    String value() default "[ unassigned ]";}

@Retention(RetentionPolicy.SOURCE)@Target(ElementType.METHOD)public @interface HttpJson {    String value() default "[ unassigned ]";    /**     * A weighting to be applied to the url, if higher it will move this url to the "top" if lower more towards the     * "bottom".     *     * @return weight     */    int weight() default 0;}

For those annotions, UrlRewriteFilter project creates a annotation processor named  UrlRewriteAnnotationProcessor to handle them.

 public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {        if (isBlank(dest)) {            if (roundEnv.processingOver())                infoMsg(getClass().getSimpleName() + ": -AurlrewriteDest not specified, annotations ignored");            return true;        }        debugMsg("process");        Set<? extends Element> urlDeclarations = roundEnv.getElementsAnnotatedWith(HttpUrl.class);        for (Element element : urlDeclarations) {            processedAnnotations.add(new ProcessedHttpUrlAnnotation(element));        }        Set<? extends Element> jsonDeclarations = roundEnv.getElementsAnnotatedWith(HttpJson.class);        for (Element element : jsonDeclarations) {            processedJsonAnnotations.add(new ProcessedHttpJsonAnnotation(element));        }        Set<? extends Element> exceptionDeclarations = roundEnv.getElementsAnnotatedWith(HttpExceptionHandler.class);        for (Element element : exceptionDeclarations) {            httpExceptionHandlers.add(new ProcessedHttpExceptionAnnotation(element));        }        if (roundEnv.processingOver()) {            if (processedAnnotations.size() > 0) {                infoMsg("Got " + processedAnnotations.size() + " @HttpUrl annotations");            }            if (processedJsonAnnotations.size() > 0) {                infoMsg("Got " + processedJsonAnnotations.size() + " @HttpJson annotations");                processedAnnotations.addAll(processedJsonAnnotations);            }            Collections.sort(processedAnnotations);            if (httpExceptionHandlers.size() > 0) {                infoMsg("Got " + httpExceptionHandlers.size() + " @HttpExceptionHandler annotations");                Collections.sort(httpExceptionHandlers);            }            try {                File destFile = new File(dest);                if (!destFile.exists()) {                    checkDirsExistMkdir(destFile.getParentFile());                    destFile.createNewFile();                }                if (!destFile.canWrite()) {                    throw new IOException("cannot write to " + destFile.getName());                }                if (errorDuringProcessing) {                    errorMsg("Error occured during processing deleting generated file.");                    destFile.delete();                } else {                    PrintWriter pw = new PrintWriter(destFile);                    infoMsg("Writing to " + destFile);                    outputRules(pw);                    outputExceptionHandlers(pw);                    pw.close();                }            } catch (FileNotFoundException e) {                errorMsg(e);                e.printStackTrace();            } catch (IOException e) {                errorMsg(e);                e.printStackTrace();            }        }        return true;    }