3. What is persistence

1. What is persistence

• Persistency is simply called as saving/storing data.
• Persistency is a term indicates permanent storage.
• Almost all applications require persistent data.
• Persistence is one of the fundamental concepts in application development.
• When we talk about persistence in Java, we’re normally talking about storing data in a relational database using SQL.

2. Types of persistent

• In java, we can save data in so many ways
1. Files Systems  → Store data in Files by using java.io
2. XML file using → By using JAXP
3. Database via sql → Store data in database by using JDBC api
4. Database via java objects → Store data in database by using ORM

3. Disadvantages of File Persistency

• Writing and reading operations are complex, because we need to write lot of java code.
• Files don’t have any common query language like SQL.
• Files can’t be used for storing large amount of data
• Files are very less secured.
• We can’t maintain relationship between data in file.

4. Disadvantages of XML File Persistency

• Using XML file is almost equal to normal files.
• Normal file stores data only, but XML file stores the data and also maintain relationship between data.
• For searching data in XML file must be loaded and parsed.
• So XML files are very slow compared to databases
• XML files also less secure.

Note : Only advantage with XML files are language independent.

5. Advantages of Database via JDBC db Persistency over File persistency

• Files are some disadvantages, so we are going to databases via JDBC.
• Databases are simple to work.
• We have common query language like SQL
• Data stored in the database is secured.
• Database can store large amount of data.
• We can maintain the relationship between data.

6. Disadvantages of Database persistency via JDBC

• If any changes on database side like adding column or deleting column, we need to change java code also.
• In real time applications, data will be store in the form java objects in java application, so for executing query we need to convert java object to text values.
• JDBC uses sql language, it is database dependent language.
• JDBC code contains lot of duplicate code.
• Connections management and transaction management are very difficult.

Note : In future we will learn advantages of database persistency via ORM .