Servlets & jdbc
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This document discusses servlets and JDBC. It explains that servlets provide a platform-independent way to build web applications using Java and have full access to Java APIs like JDBC for interacting with databases. The document then describes the lifecycle of servlets, including initialization, processing requests, and destruction. It also discusses how servlets can handle GET and POST requests. Finally, the document provides an overview of JDBC, describing it as the Java API for connecting to and executing queries on databases.
Servlets & jdbc
- 1. SERVLETS & JDBC BY K.SIVAPRIYA MS.c(Info.tech) Nadar Saraswathi College Of Arts &Science
- 2. SERVLETS Servlets provide a component-based, platform- independent method for building Web-based applications, without the performance limitations of CGI programs. Servlets have access to the entire family of Java APIs, including the JDBC API to access enterprise databases
- 3. Why to Learn Servlet? Using Servlets, you can collect input from users through web page forms, present records from a database or another source, and create web pages dynamically. Java Servlets often serve the same purpose as programs implemented using the Common Gateway Interface (CGI). But Servlets offer several advantages in comparison with the CGI.
- 4. CONT… Performance is significantly better. Servlets execute within the address space of a Web server. It is not necessary to create a separate process to handle each client request. Servlets are platform-independent because they are written in Java.
- 5. CONT… Java security manager on the server enforces a set of restrictions to protect the resources on a server machine. So servlets are trusted. The full functionality of the Java class libraries is available to a servlet. It can communicate with applets, databases, or other software via the sockets and RMI mechanisms that you have seen already.
- 6. LIFE CYCLE OF SERVELTS A servlet life cycle can be defined as the entire process from its creation till the destruction. The following are the paths followed by a servlet. The servlet is initialized by calling the init() method. The servlet calls service() method to process a client's request. The servlet is terminated by calling the destroy() method.
- 7. CONT… Finally, servlet is garbage collected by the garbage collector of the JVM. Now let us discuss the life cycle methods in detail.
- 8. init() Method The init method is called only once. It is called only when the servlet is created, and not called for any user requests afterwards. So, it is used for one-time initializations, just as with the init method of applets. The servlet is normally created when a user first invokes a URL corresponding to the servlet, but you can also specify that the servlet be loaded when the server is first started.
- 9. CONT… When a user invokes a servlet, a single instance of each servlet gets created, with each user request resulting in a new thread that is handed off to doGet or doPost as appropriate. The init() method simply creates or loads some data that will be used throughout the life of the servlet. The init method definition looks like this public void init() throws ServletException { // Initialization code... }
- 10. service() Method The service() method is the main method to perform the actual task. The servlet container calls the service() method to handle requests coming from the client and to write the formatted response back to the client. Each time the server receives a request for a servlet, the server spawns a new thread and calls service. The service() method checks the HTTP request type (GET, POST, PUT, DELETE, etc.) and calls doGet, doPost, doPut, doDelete, etc. methods as appropriate.
- 11. doGet() Method & doPost() Method • A GET request results from a normal request for a URL or from an HTML form that has no METHOD specified and it should be handled by doGet() method. • A POST request results from an HTML form that specifically lists POST as the METHOD and it should be handled by doPost() method.
- 12. destroy() Method The destroy() method is called only once at the end of the life cycle of a servlet. This method gives your servlet a chance to close database connections, halt background threads, write cookie lists or hit counts to disk, and perform other such cleanup activities. After the destroy() method is called, the servlet object is marked for garbage collection.
- 13. JDBC JDBC stands for Java Database Connectivity. JDBC is a Java API to connect and execute the query with the database. It is a part of JavaSE (Java Standard Edition). JDBC API uses JDBC drivers to connect with the database. There are four types of JDBC drivers: • JDBC-ODBC Bridge Driver, • Native Driver, • Network Protocol Driver, and • Thin Driver
- 14. CONT… We can use JDBC API to access tabular data stored in any relational database. By the help of JDBC API, we can save, update, delete and fetch data from the database. It is like Open Database Connectivity (ODBC) provided by Microsoft. The current version of JDBC is 4.3. It is the stable release since 21st September, 2017. It is based on the X/Open SQL Call Level Interface. The java.sql package contains classes and interfaces for JDBC API.
- 15. A list of popular interfaces of JDBC API • Driver interface • Connection interface • Statement interface • Prepared Statement interface • CallableStatement interface • ResultSet interface • ResultSetMetaData interface • DatabaseMetaData interface • RowSet interface