spring-boot-starter-data-jpa 中的 Eaxmple 如何使用

本文只简单介绍精确匹配（sql中 'where ** = **'）、字符串搜索（sql中'where ** like %name%'）。

如果需要更多高级应用，可以参考spring jpa官方示例，传送门。

一.准备工作

1.创建一个标准的spring boot jpa程序，并配置数据库连接

pom.xml

...

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

...

2.实体类 User.java

...
@Entity
public class User {

@Id
@GeneratedValue
private Integer id;

private String name;

private Short type;

@Override
public String toString() {
return "User{" +
"id=" + id +
", name='" + name + '\'' +
", type=" + type +
'}';
}
//... setter / getter..
}

3.Repository UserRepository.java

...
import org.springframework.data.jpa.repository.JpaRepository;

public interface UserRepository extends JpaRepository<User, Integer> {}

二.测试程序 UserService.java ，运行 Application 即可看到结果

@Component
@Transactional
public class UserService {

private final UserRepository userRepository;

private Logger logger = LoggerFactory.getLogger(this.getClass());

@Autowired
public UserService(UserRepository userRepository) {
this.userRepository = userRepository;

//初始化数据
init();

//测试查新
printAll("通过 Example 精确查找数据", queryByExample());
printAll("通过 Example 字符串匹配", queryByExampleMatcher());
}

Collection<User> queryByExample() {
User user = new User();
user.setType((short) 1);

Example<User> userExample = Example.of(user);

return userRepository.findAll(userExample);

}

Collection<User> queryByExampleMatcher() {

User user = new User();
user.setName("10010");

Example<User> userExample = Example.of(user, ExampleMatcher.matching().withMatcher("name",
/*startsWith -> 10010%
* endsWith -> %10010
* contains -> %10010%
* */
ExampleMatcher.GenericPropertyMatchers.startsWith()));

return userRepository.findAll(userExample);
}

void printAll(String pre, Collection<User> userIterator) {
logger.info("遍历 用户列表 {}", pre);

for (User u : userIterator) {
logger.info(u.toString());
}
}

void init() {
for (int i = 0; i < 443; i++) {
userRepository.save(new User(("100" + i + "00111" + i), (short) (i % 3)));
}
}

}