基与上一篇文章 SpringData JPA 入门小 demo , 我们继续深入了解 Specifications 动态查询.

基于上一篇文章所建立的开发环境, 我们接着创建新的测试包, 来学习 Specifications 接口动态查询入门小 demo

一. 创建新的测试类

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:applicationContext.xml")
public class SpecTest {

    @Autowired
    private CustomerDao customerDao;


}

1. 单条件查询对象 - equal(String str, String str);

@Test
public void testFindByCondition() {
    Specification<Customer> spec = new Specification<Customer>() {
        public Predicate toPredicate(Root<Customer> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
            Path<Object> custName = root.get("custName");
            Predicate predicate = cb.equal(custName, "张三");
            return predicate;
        }
    };
    Customer customer = customerDao.findOne(spec);
    System.out.println(customer);
}

2. 多条件查询对象 - and(Predicate p1, Predicate p2);  or(Predicate p1, Predicate p2);

@Test
public void testFindBySeveralCondition() {
    Specification<Customer> spec = new Specification<Customer>() {
        public Predicate toPredicate(Root<Customer> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
            Path<Object> custName = root.get("custName");
            Path<Object> custIndustry = root.get("custIndustry");
            Predicate p1 = cb.equal(custName, "张三");
            Predicate p2 = cb.equal(custIndustry, "it行业");
            Predicate and = cb.and(p1, p2);   //以 与 的形式拼接多个查询条件
            //Predicate or =  cb.or(p1, p2);   //以 或 的形式拼接多个查询条件
            return and;
        }
    };
    Customer customer = customerDao.findOne(spec);
    System.out.println(customer);
}

3. 模糊查询 - like();

     排序 - Sort sort = new Sort(Sort.Direction.DESC, 排序的字段名);

@Test
public void testLike() {
    Specification<Customer> spec = new Specification<Customer>() {
        public Predicate toPredicate(Root<Customer> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
            Path<Object> custName = root.get("custName");
            Predicate like = cb.like(custName.as(String.class), "张%");
            return like;
        }
    };
    //添加排序
    //Sort.Direction.DESC: 倒序
    //Sort.Direction.ASC: 升序
    Sort sort = new Sort(Sort.Direction.DESC, "custName");
    List<Customer> list = customerDao.findAll(spec, sort);
    for (Customer customer : list) {
        System.out.println(customer);
    }
}

4. 分页查询

@Test
public void testPage() {
    Specification spec = null;
    Pageable pageable = new PageRequest(0, 10);
    Page<Customer> page = customerDao.findAll(null, pageable);
    System.out.println(page.getContent());  //得到数据集合列表
    System.out.println(page.getTotalElements());  //得到总条数
    System.out.println(page.getTotalPages());  //得到总页数
}

源码下载: https://pan.baidu.com/s/1JLc4zABzZBzoy4JhJNNJpg