The application and technical principles of the MapperDao framework in the Java library
The MapperDao framework is an ORM (object relationship mapping) framework for the Java class library, which can simplify database operations and improve development efficiency.This article will introduce the application and technical principles of the MapperDao framework in the Java class library, and provide the corresponding Java code example.
1. Application of MapperDao framework
The MapperDao framework is mainly used in the database operation in the Java class library. It can map the database table to the Java object to achieve additional, deletion, and inspection operation of the database.The use of the Mapperdao framework in the Java library can enable developers to focus more on the realization of business logic without paying attention to the underlying database operation.
The specific steps of using the Mapperdao framework in the Java class library are as follows:
1. Define the entity class (Entity): In the Java class library, the database table is required to map the database table as a physical class.For example, if there is a database table called "User", it can define a physical class called "UseRENTITY", which contains member variables corresponding to database table fields.
The example code is as follows:
public class UserEntity {
private int id;
private String name;
// Other fields ...
// Getters和Setters...
}
2. Define the Mapper interface (Mapper): Mapper interface defines methods related to database operations. Through this interface, CRUD operations for databases can be achieved.
The example code is as follows:
@DAO
public interface UserMapper {
@Select(sql = "SELECT * FROM user WHERE id = /*id*/1", returnType = UserEntity.class)
UserEntity getById(@Param("id") int id);
@Insert
void insert(UserEntity user);
@Update
void update(UserEntity user);
@Delete(sql = "DELETE FROM user WHERE id = /*id*/1")
void deleteById(@Param("id") int id);
}
3. Configure the MapperDao framework: Add the configuration information of the MapperDao framework in the configuration file of the Java class library, such as database connection information, the mapping relationship between the physical class and the Mapper interface.
The example code is as follows:
<mapper-dao-config>
<jdbc url="jdbc:mysql://localhost:3306/db_name" driverClass="com.mysql.jdbc.Driver"
username="username" password="password" />
<entities>
<entity class="com.example.UserEntity" tableName="user" />
</entities>
</mapper-dao-config>
4. Use the MapperDao framework to perform a database operation: In the Java class library, by calling the method defined in the Mapper interface, the CRUD operation of the database can be achieved.
The example code is as follows:
public class UserDao {
private final UserMapper userMapper;
public UserDao() {
userMapper = MapperDaoFactory.getMapper(UserMapper.class);
}
public UserEntity getUserById(int id) {
return userMapper.getById(id);
}
public void insertUser(UserEntity user) {
userMapper.insert(user);
}
public void updateUser(UserEntity user) {
userMapper.update(user);
}
public void deleteUserById(int id) {
userMapper.deleteById(id);
}
}
2. Technical principles for the MapperDao framework
The MapperDao framework is based on the Java annotation and reflection mechanism to implement a mapping between database tables and Java objects.Its technical principles mainly include the following aspects:
1. Note definition: A series of annotations are used in the Mapperdao framework to define the database table, field and database operation -related methods.For example, use the @DAO annotation to mark the Mapper interface,@select annotation definition query statement,@insert,@update,@delete annotation definition increase, delete, changing sentences, etc.
2. Reflective mechanism: The MapperDao framework obtains the relevant information of the physical class and Mapper interface through the reflection mechanism, and dynamically generates the corresponding SQL statement according to the content of the annotation definition.By reflection, the encapsulation of the query results can also be achieved, and the database query results can be mapped as the Java object.
3. Database connection management: Mapperdao framework through the configuration of the information in the file, management with the database connection.It can automatically obtain the database connection, execute SQL statements, and return the result based on the database connection information in the configuration file.
4. Cache mechanism: Mapperdao framework uses the cache mechanism to improve the efficiency of database access.It caches the results that have been queried to reduce frequent inquiries of databases.At the same time, when the addition and deletion and modification operation is performed, the cache will be automatically updated to ensure the consistency of the cache and the database.
Summarize:
The application and technical principles of the MapperDao framework in the Java library mainly include the steps of defining physical classes and Mapper interfaces, configuration framework information, and database operations using the framework.The mapping of the database table and the Java object through annotations and reflection mechanisms provides a convenient way for CRUD operations.At the same time, the framework also supports the cache mechanism, which improves the efficiency of database operations.The above is the introduction of the application and technical principles of the MapperDao framework in the Java class library.
