Question

I have a function that creates URLs for requests as follows:

public String createUrl(String path, String filename) {
        return new StringBuilder(path).append("?filename=").append(filename).toString();
        }

Now, what I want to do is to add another parameter to the URL called transactionId. A naive implementation would be:

 public String createUrl(String path, String filename,String transactionId) {
            return new StringBuilder(path).append("?filename=").append(filename).append("?transactionId=").append(transactionId).toString();
            }

or I can have a static method somewhere that returns a transactionID and modify the code as follows:

 public String createUrl(String path, String filename) {
            return new StringBuilder(path).append("?filename=").append(filename).append("?transactionId=").append(TransactionMonitor.getTransactionId()).toString();
            }

Both of these approaches makes me modify the preexisting code. Is there an approach that I can take to decorate the url returned by the method with new parameters. Also, it will be great if the solution is configurable.

Thanks

Answer 1

You can create UrlBuilder class that builds url for you:

class UrlBuilder {

    private String path;

    private Map<String, String> parameters = new LinkedHashMap<String, String>();

    public UrlBuilder path(String path) {
        this.path = path;
        return this;
    }

    public UrlBuilder parameter(String param, String value) {
        parameters.add(param, value);
        return this;
    }


    public String build() {
        String paramsString = "";

        for (Map.Entry<String, String> entry: parameters.entrySet()) {
            if (paramsString.isEmpty()) {
                paramsString += "?";
            }
            paramsString += params.getKey() + "=" + params.getValue();
        }

        return path + paramsString;
    }

}

and use it in your code

new UrlBuilder().path("http://google.com").params("q", "java").build()