【设计模式】JAVA Design Patterns——Data Access Object（数据访问对象模式）

🔍目的

对象为某种类型的数据库或其他持久性机制提供了抽象接口。

🔍解释

真实世界例子

有一组客户数据需要持久化到数据库中。我们需要整个额外的增删改查操作以便操作客户数据。

通俗描述

DAO是我们通过基本持久性机制提供的接口。

维基百科

在计算机软件中，数据访问对象（DAO）是一种模式，可为某种类型的数据库或其他持久性机制提供抽象接口。

程序示例

创建客户实体：

public class Customer {private int id;private String firstName;private String lastName;public Customer(int id, String firstName, String lastName) {this.id = id;this.firstName = firstName;this.lastName = lastName;}// getters and setters ->...
}

创建CustomerDao接口及其两个不同的实现。

public interface CustomerDao {Stream<Customer> getAll() throws Exception;Optional<Customer> getById(int id) throws Exception;boolean add(Customer customer) throws Exception;boolean update(Customer customer) throws Exception;boolean delete(Customer customer) throws Exception;
}public class InMemoryCustomerDao implements CustomerDao {private final Map<Integer, Customer> idToCustomer = new HashMap<>();// implement the interface using the map...
}public class DbCustomerDao implements CustomerDao {private static final Logger LOGGER = LoggerFactory.getLogger(DbCustomerDao.class);private final DataSource dataSource;public DbCustomerDao(DataSource dataSource) {this.dataSource = dataSource;}// implement the interface using the data source...

使用DAO管理客户数据的方式：

    final var dataSource = createDataSource();createSchema(dataSource);final var customerDao = new DbCustomerDao(dataSource);addCustomers(customerDao);log.info(ALL_CUSTOMERS);try (var customerStream = customerDao.getAll()) {customerStream.forEach((customer) -> log.info(customer.toString()));}log.info("customerDao.getCustomerById(2): " + customerDao.getById(2));final var customer = new Customer(4, "Dan", "Danson");customerDao.add(customer);log.info(ALL_CUSTOMERS + customerDao.getAll());customer.setFirstName("Daniel");customer.setLastName("Danielson");customerDao.update(customer);log.info(ALL_CUSTOMERS);try (var customerStream = customerDao.getAll()) {customerStream.forEach((cust) -> log.info(cust.toString()));}customerDao.delete(customer);log.info(ALL_CUSTOMERS + customerDao.getAll());deleteSchema(dataSource);

程序输出：

customerDao.getAllCustomers(): 
Customer{id=1, firstName='Adam', lastName='Adamson'}
Customer{id=2, firstName='Bob', lastName='Bobson'}
Customer{id=3, firstName='Carl', lastName='Carlson'}
customerDao.getCustomerById(2): Optional[Customer{id=2, firstName='Bob', lastName='Bobson'}]
customerDao.getAllCustomers(): java.util.stream.ReferencePipeline$Head@7cef4e59
customerDao.getAllCustomers(): 
Customer{id=1, firstName='Adam', lastName='Adamson'}
Customer{id=2, firstName='Bob', lastName='Bobson'}
Customer{id=3, firstName='Carl', lastName='Carlson'}
Customer{id=4, firstName='Daniel', lastName='Danielson'}
customerDao.getAllCustomers(): java.util.stream.ReferencePipeline$Head@2db0f6b2
customerDao.getAllCustomers(): 
Customer{id=1, firstName='Adam', lastName='Adamson'}
Customer{id=2, firstName='Bob', lastName='Bobson'}
Customer{id=3, firstName='Carl', lastName='Carlson'}
customerDao.getCustomerById(2): Optional[Customer{id=2, firstName='Bob', lastName='Bobson'}]
customerDao.getAllCustomers(): java.util.stream.ReferencePipeline$Head@12c8a2c0
customerDao.getAllCustomers(): 
Customer{id=1, firstName='Adam', lastName='Adamson'}
Customer{id=2, firstName='Bob', lastName='Bobson'}
Customer{id=3, firstName='Carl', lastName='Carlson'}
Customer{id=4, firstName='Daniel', lastName='Danielson'}
customerDao.getAllCustomers(): java.util.stream.ReferencePipeline$Head@6ec8211c