private String replacePattern()

in commons-email2-jakarta/src/main/java/org/apache/commons/mail2/jakarta/ImageHtmlEmail.java [113:171]
34 lines of code
7 McCabe index (conditional complexity)

    private String replacePattern(final String htmlMessage, final Pattern pattern) throws EmailException, IOException {
        DataSource dataSource;
        final StringBuffer stringBuffer = new StringBuffer();

        // maps "cid" --> name
        final Map<String, String> cidCache = new HashMap<>();

        // maps "name" --> dataSource
        final Map<String, DataSource> dataSourceCache = new HashMap<>();

        // in the String, replace all "img src" with a CID and embed the related
        // image file if we find it.
        final Matcher matcher = pattern.matcher(htmlMessage);

        // the matcher returns all instances one by one
        while (matcher.find()) {
            // in the RegEx we have the <src> element as second "group"
            final String resourceLocation = matcher.group(2);

            // avoid loading the same data source more than once
            if (dataSourceCache.get(resourceLocation) == null) {
                // in lenient mode we might get a 'null' data source if the resource was not found
                dataSource = getDataSourceResolver().resolve(resourceLocation);

                if (dataSource != null) {
                    dataSourceCache.put(resourceLocation, dataSource);
                }
            } else {
                dataSource = dataSourceCache.get(resourceLocation);
            }

            if (dataSource != null) {
                String name = dataSource.getName();
                if (EmailUtils.isEmpty(name)) {
                    name = resourceLocation;
                }

                String cid = cidCache.get(name);

                if (cid == null) {
                    cid = embed(dataSource, name);
                    cidCache.put(name, cid);
                }

                // if we embedded something, then we need to replace the URL with
                // the CID, otherwise the Matcher takes care of adding the
                // non-replaced text afterwards, so no else is necessary here!
                matcher.appendReplacement(stringBuffer, Matcher.quoteReplacement(matcher.group(1) + "cid:" + cid + matcher.group(3)));
            }
        }

        // append the remaining items...
        matcher.appendTail(stringBuffer);

        cidCache.clear();
        dataSourceCache.clear();

        return stringBuffer.toString();
    }