Web server VS. application server
1. What is Web Server?
When we have an application program that has static contents such as texts, images, audio, and video files, etc. Say, an HTML page (HTML, CSS, JS), we need an execution engine that would be able to execute the static contents called a web server. Example: Apache HTTP Server.
How web server works?
- A client (web browser) sends an HTTP GET request to the web server, asking for a specific resource(texts, images, media etc.)
- The web server retrieves the client’s requested information from its directory and returns it back to the client as an HTTP response.
- The client (web browser) renders the static content.
2. What is Java EE Servers?
Along with the above functionalities of the web server, if we have some requirement of dynamic contents or functionalities (say, a DB where we want to insert, update or view some transactions) or JSPs (Java Servlet Pages). In order to fulfill these scenarios, we need a server that can run Java programs (servlets) called Java application servers or java-enabled small scale application servers. Example: Tomcat
Notes:
1. Servlet: A servlet is a java program that runs on java enabled application server.
2. JSP: It is used to add the Java code to the HTML or XML document.
3. What is Application Server?
When we have a requirement in an application to serve static content and dynamic content along with the need for business logic, i.e., the EJB (Enterprise Java Beans). The EJBs are specific for developing large-scale, distributed business applications on the Java platform.
Examples:
- Session Bean: For developing business logic and workflow
- Entity Bean: It is used to represent the persistent data stored in the database
- Message Driven Bean: Used for asynchronous process of JMS
Now, in order to serve these enterprise beans, we need an EJB container that is a Java-enabled full-scale application server which helps the application for high availability, scalability, load balancing, failure, etc. Example: JBoss.
Key Insights
- When we install a web server, we don’t need Java in our system.
- When we install Tomcat, we need Java, as it can run servlets or JSPs that need Java.
- When it comes to EJB, apart from static or dynamic content, we have business code developed in EJB. We need a full-scale application server.