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使用 Spring Data Specification 构建 REST 查询语言

1、概览 {#1概览}

上一篇文章 介绍了一个基于 JPA Criteria 的查询语言解决方案。

本文将带你了解如何使用 Spring Data JPASpecification 构建一个搜索/过滤 REST API。

2、 User 实体 {#2-user-实体}

创建一个 User 实体类,用于检索 API:

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String firstName;
    private String lastName;
    private String email;

    private int age;
    
    // get、set 方法
}

3、使用 Specification 进行过滤 {#3使用-specification-进行过滤}

来看看如何使用自定义 Spring Data JPA Specification 进行查询。

创建一个实现 Specification 接口的 UserSpecification,并传入自己的约束条件来构建实际查询:

public class UserSpecification implements Specification<User> {

    private SearchCriteria criteria;

    @Override
    public Predicate toPredicate
      (Root<User> root, CriteriaQuery<?> query, CriteriaBuilder builder) {
 
        if (criteria.getOperation().equalsIgnoreCase(">")) {
            return builder.greaterThanOrEqualTo(
              root.<String> get(criteria.getKey()), criteria.getValue().toString());
        } 
        else if (criteria.getOperation().equalsIgnoreCase("<")) {
            return builder.lessThanOrEqualTo(
              root.<String> get(criteria.getKey()), criteria.getValue().toString());
        } 
        else if (criteria.getOperation().equalsIgnoreCase(":")) {
            if (root.get(criteria.getKey()).getJavaType() == String.class) {
                return builder.like(
                  root.<String>get(criteria.getKey()), "%" + criteria.getValue() + "%");
            } else {
                return builder.equal(root.get(criteria.getKey()), criteria.getValue());
            }
        }
        return null;
    }
}

如上,我们根据一些简单的约束条件创建了一个 Specification,包含这些约束条件的 SearchCriteria 类如下:

public class SearchCriteria {
    private String key;
    private String operation;
    private Object value;
}

SearchCriteria 实现包含一个约束条件的基本表示,我们会根据这个约束条件来构建查询:

  • key:字段名,如 nameage 等。
  • operation:操作,例如等于、小于等。
  • value:字段值,如 john25 等。

当然,这种实现方式比较简单,还可以改进。不过,它为我们所需的强大而灵活的操作奠定了坚实的基础。

4、UserRepository {#4userrepository}

接着,来看看 UserRepository

只需继承 JpaSpecificationExecutor 即可获得 Specification API:

public interface UserRepository 
  extends JpaRepository<User, Long>, JpaSpecificationExecutor<User> {}

5、测试搜索过滤 {#5测试搜索过滤}

首先,创建几个用户,用于测试:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = { PersistenceJPAConfig.class })
@Transactional
@TransactionConfiguration
public class JPASpecificationIntegrationTest {

    @Autowired
    private UserRepository repository;

    private User userJohn;
    private User userTom;

    @Before
    public void init() {
        userJohn = new User();
        userJohn.setFirstName("John");
        userJohn.setLastName("Doe");
        userJohn.setEmail("john@doe.com");
        userJohn.setAge(22);
        repository.save(userJohn);

        userTom = new User();
        userTom.setFirstName("Tom");
        userTom.setLastName("Doe");
        userTom.setEmail("tom@doe.com");
        userTom.setAge(26);
        repository.save(userTom);
    }
}

根据 lastName 检索用户:

@Test
public void givenLast_whenGettingListOfUsers_thenCorrect() {
    UserSpecification spec = 
      new UserSpecification(new SearchCriteria("lastName", ":", "doe"));
    
    List<User> results = repository.findAll(spec);

    assertThat(userJohn, isIn(results));
    assertThat(userTom, isIn(results));
}

根据 firstNamelastName 检索用户:

@Test
public void givenFirstAndLastName_whenGettingListOfUsers_thenCorrect() {
    UserSpecification spec1 = 
      new UserSpecification(new SearchCriteria("firstName", ":", "john"));
    UserSpecification spec2 = 
      new UserSpecification(new SearchCriteria("lastName", ":", "doe"));
    
    List<User> results = repository.findAll(Specification.where(spec1).and(spec2));

    assertThat(userJohn, isIn(results));
    assertThat(userTom, not(isIn(results)));
}

注意 :这里使用 whereand 来合并 Specification

检索 lastName 等于 doe 并且 age 大于 25 的用户:

@Test
public void givenLastAndAge_whenGettingListOfUsers_thenCorrect() {
    UserSpecification spec1 = 
      new UserSpecification(new SearchCriteria("age", ">", "25"));
    UserSpecification spec2 = 
      new UserSpecification(new SearchCriteria("lastName", ":", "doe"));

    List<User> results = 
      repository.findAll(Specification.where(spec1).and(spec2));

    assertThat(userTom, isIn(results));
    assertThat(userJohn, not(isIn(results)));
}

检索不存在的用户:

@Test
public void givenWrongFirstAndLast_whenGettingListOfUsers_thenCorrect() {
    UserSpecification spec1 = 
      new UserSpecification(new SearchCriteria("firstName", ":", "Adam"));
    UserSpecification spec2 = 
      new UserSpecification(new SearchCriteria("lastName", ":", "Fox"));

    List<User> results = 
      repository.findAll(Specification.where(spec1).and(spec2));

    assertThat(userJohn, not(isIn(results)));
    assertThat(userTom, not(isIn(results)));  
}

根据 firstName 模糊检索:

@Test
public void givenPartialFirst_whenGettingListOfUsers_thenCorrect() {
    UserSpecification spec = 
      new UserSpecification(new SearchCriteria("firstName", ":", "jo"));
    
    List<User> results = repository.findAll(spec);

    assertThat(userJohn, isIn(results));
    assertThat(userTom, not(isIn(results)));
}

6、组合 Specification {#6组合-specification}

实现一个 UserSpecificationsBuilder 来把自定义的 Specification 组起来,以使用多个约束条件并根据多个条件进行过滤。

SpecSearchCriteria 如下:

public class SpecSearchCriteria {

    private String key;
    private SearchOperation operation;
    private Object value;
    private boolean orPredicate;

    public boolean isOrPredicate() {
        return orPredicate;
    }
}

UserSpecificationsBuilder 如下:

public class UserSpecificationsBuilder {
    
    private final List<SpecSearchCriteria> params;

    public UserSpecificationsBuilder() {
        params = new ArrayList<>();
    }

    public final UserSpecificationsBuilder with(String key, String operation, Object value, 
      String prefix, String suffix) {
        return with(null, key, operation, value, prefix, suffix);
    }

    public final UserSpecificationsBuilder with(String orPredicate, String key, String operation, 
      Object value, String prefix, String suffix) {
        SearchOperation op = SearchOperation.getSimpleOperation(operation.charAt(0));
        if (op != null) {
            if (op == SearchOperation.EQUALITY) { // 该操作可能是复杂的操作
                boolean startWithAsterisk = prefix != null &amp;& 
                  prefix.contains(SearchOperation.ZERO_OR_MORE_REGEX);
                boolean endWithAsterisk = suffix != null && 
                  suffix.contains(SearchOperation.ZERO_OR_MORE_REGEX);

                if (startWithAsterisk && endWithAsterisk) {
                    op = SearchOperation.CONTAINS;
                } else if (startWithAsterisk) {
                    op = SearchOperation.ENDS_WITH;
                } else if (endWithAsterisk) {
                    op = SearchOperation.STARTS_WITH;
                }
            }
            params.add(new SpecSearchCriteria(orPredicate, key, op, value));
        }
        return this;
    }

    public Specification build() {
        if (params.size() == 0)
            return null;

        Specification result = new UserSpecification(params.get(0));
     
        for (int i = 1; i < params.size(); i++) {
            result = params.get(i).isOrPredicate()
              ? Specification.where(result).or(new UserSpecification(params.get(i))) 
              : Specification.where(result).and(new UserSpecification(params.get(i)));
        }
        
        return result;
    }
}

7、UserController {#7usercontroller}

最后,创建一个 REST API 来使用搜索/过滤功能:

@Controller
public class UserController {

    @Autowired
    private UserRepository repo;

    @RequestMapping(method = RequestMethod.GET, value = "/users")
    @ResponseBody
    public List<User> search(@RequestParam(value = "search") String search) {
        UserSpecificationsBuilder builder = new UserSpecificationsBuilder();
        Pattern pattern = Pattern.compile("(\\w+?)(:|<|>)(\\w+?),");
        Matcher matcher = pattern.matcher(search + ",");
        while (matcher.find()) {
            builder.with(matcher.group(1), matcher.group(2), matcher.group(3));
        }
        
        Specification<User> spec = builder.build();
        return repo.findAll(spec);
    }
}

注意,可以更改 Pattern 对象来支持其他非英语系统。

Pattern pattern = Pattern.compile("(\\w+?)(:|<|>)(\\w+?),", Pattern.UNICODE_CHARACTER_CLASS);

测试 API:

http://localhost:8080/users?search=lastName:doe,age>25

响应如下:

[{
    "id":2,
    "firstName":"tom",
    "lastName":"doe",
    "email":"tom@doe.com",
    "age":26
}]

Pattern 中,搜索由逗号 "," 分割,因此搜索条件不能包含该字符。该 Pattern 也不匹配空白。

如果要搜索包含逗号,可以考虑使用不同的分隔符,如 ";"。

另一种方法是更改 Pattern,搜索引号之间的值,然后从搜索条件中去除这些引号:

Pattern pattern = Pattern.compile("(\\w+?)(:|<|>)(\"([^\"]+)\")");

8、总结 {#8总结}

本文介绍了如何使用 Spring Data Specification 来构建 REST 查询语言,还介绍了如何在 Rest API 中使用该语言进行数据过滤。


Ref:https://www.baeldung.com/rest-api-search-language-spring-data-specifications

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