* - Uppercase letters (A-Z)
     * - Digits (0-9)
     * - Special characters: . - * _ : / + % = & ? # [ ] @ ~ ! $ ' ( ) , ;
     *
     * @param c the character to check
     * @return {@code true} if the character is a valid URL character, {@code false} otherwise
     */
    public static boolean isUrlChar(final char c) {
        if (c >= 'a' && c <= 'z' //
                || c >= 'A' && c <= 'Z' //

            System.setOut(new PrintStream(outStream, true));
            final PrintStream originalErrStream = System.err;
            final ByteArrayOutputStream errStream = new ByteArrayOutputStream();
            System.setErr(new PrintStream(errStream, true));
            try {

     * A header is considered valid if its name is not blank and its value is not null.
     * @return true if the header is valid, false otherwise.
     */
    public boolean isValid() {
        if (StringUtil.isBlank(name) || value == null) {
            return false;
        }

        return true;
    }

                final Matcher matcher = pattern.matcher(url);
                if (matcher.matches()) {
                    match = true;
                }
            }
            if (match) {
                return false;
            }
        }

        return true;
    }

    /*
     * (non-Javadoc)
     *
     * @see org.codelibs.fess.crawler.filter.UrlFilter#processUrl(java.lang.String)

     */
    /**
     * Checks if the rule manager contains the specified rule.
     * @param rule the rule to check for
     * @return true if the rule is present, false otherwise
     */
    @Override
    public boolean hasRule(final Rule rule) {
        return ruleList.contains(rule);
    }

    /*
     * (non-Javadoc)
     *

        constructor.setAccessible(true);

        // Test with suppression enabled and writable stack trace
        String message1 = "Test with suppression enabled";
        CrawlerSystemException exception1 = constructor.newInstance(message1, true, true);
        assertNotNull(exception1);
        assertEquals(message1, exception1.getMessage());

        try {
            final File tempFile = File.createTempFile(prefix, suffix, directory);
            tempFile.setReadable(false, false);
            tempFile.setReadable(true, true);
            tempFile.setWritable(false, false);
            tempFile.setWritable(true, true);
            return tempFile;
        } catch (final IOException e) {
            throw new CrawlerSystemException("Could not create a temp file.", e);
        }

     * Returns whether SIDs (Security Identifiers) should be resolved.
     *
     * @return true if SIDs should be resolved, false otherwise
     */
    public boolean isResolveSids() {
        return resolveSids;
    }

    /**
     * Sets whether SIDs (Security Identifiers) should be resolved.
     *
     * @param resolveSids true to resolve SIDs, false otherwise
     */

Crawler crawler2 = container.getComponent("crawler");  
crawler2.setSessionId("session2");
crawler2.addUrl("https://site2.com");

// Execute concurrently
crawler1.setBackground(true);
crawler2.setBackground(true);

String sessionId1 = crawler1.execute();
String sessionId2 = crawler2.execute();

crawler1.awaitTermination();
crawler2.awaitTermination();
```

### Custom Interval Control

     * Checks if the crawler is running in background mode.
     * @return true if in background mode, false otherwise.
     */
    public boolean isBackground() {
        return background;
    }

    /**
     * Sets the background mode for the crawler.
     * If true, the execute method will not wait for termination.
     * @param background true to run in background, false otherwise.
     */