Since Apache Solr is a J2EE-based WAR file, it can be easily integrated with any other application. We have already seen how Apache Solr can be used on different J2EE application containers such as Tomcat and Jetty. For the applications that are developed on the J2EE platform, Apache Solr can be used in the following ways in your existing J2EE applications. While many Solr implementations go for HTML APIs with an XML/JSON request-response model from the client, the approaches discussed in the latter part of the chapter highlight a tighter integration with Apache Solr. HTML-based integration of Apache Solr demands consumer application to send HTTP requests to the Solr server, and accept responses in the XML/JSON format.