How is the data access layer in the Java Spring framework designed?

In the Spring framework, the data access layer (DAO) is used for the interaction between the application and the database, using JDBC or JPA to communicate with the database. JDBC data access involves using JDBC Template to perform SQL queries and updates, while JPA data access uses entity classes and annotations to map database tables and objects and perform JPA queries and updates through JPA Template. In actual combat, you can use the Spring framework to create a JDBC DAO, by creating a DataSource bean, a JDBC Template bean and implementing the methods in the UserDao interface.

Data access layer design in Java Spring framework

The data access layer (DAO) is the application responsible for interacting with the database s component. In the Spring framework, DAO usually uses JDBC (Java Database Connectivity) or JPA (Java Persistence API) to communicate with the database.

JDBC Data Access

Implementing DAO using JDBC involves creating a JDBC Template that provides methods for performing SQL queries and updates. JDBC Template simplifies low-level operations of JDBC and provides error handling out of the box.

import org.springframework.jdbc.core.JdbcTemplate;
import javax.sql.DataSource;

public class JdbcUserDao implements UserDao {

    private JdbcTemplate jdbcTemplate;

    public JdbcUserDao(DataSource dataSource) {
        this.jdbcTemplate = new JdbcTemplate(dataSource);
    }

    public User findUserById(int id) {
        return jdbcTemplate.queryForObject(
            "SELECT * FROM users WHERE id = ?",
            new Object[]{id},
            new BeanPropertyRowMapper(User.class)
        );
    }
}

JPA Data Access

JPA provides a more advanced way to interact with the database. It uses entity classes and annotations to map database tables and objects. JPA Template provides a convenient way to perform JPA queries and updates.

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

public class JpaUserDao implements UserDao {

    @PersistenceContext
    private EntityManager entityManager;

    public User findUserById(int id) {
        return entityManager.find(User.class, id);
    }
}

Practical case

The following is a practical case using the Spring framework to create a simple JDBC DAO:

1. Create DataSource bean : Use the DataSource bean provided by the Spring framework to create a connection to the database.
2. Create JDBC Template bean: Use DataSource bean to create JDBC Template bean.
3. Implement the UserDao interface: Create the JdbcUserDao class and implement the methods defined in the UserDao interface.

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;

@Repository
public class JdbcUserDao implements UserDao {

    @Autowired
    private JdbcTemplate jdbcTemplate;

    @Override
    public User findUserById(int id) {
        return jdbcTemplate.queryForObject(
            "SELECT * FROM users WHERE id = ?",
            new Object[]{id},
            new BeanPropertyRowMapper(User.class)
        );
    }
}

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