Springboot中对jpa动态查询条件的封装

jpa对于固定参数的条件查询比较简单，可以在Repository中直接用参数名来查询。但是对于不固定的参数查询就比较麻烦了，官方提供的是继承JpaSpecificationExecutor，然后自己拼接Specification。这一篇主要是对Specification进行封装，让写法更友好.
代码参考：http://lee1177.iteye.com/blog/1994295。感觉还不够完整，回头使用中再补上。

一：自定义Specification

创建条件表达式接口，模拟系统的条件查询

import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;

/** * 条件接口 * 用户提供条件表达式接口 * * @Class Name Criterion * @Author lee * @Create In 2012-2-8 */
public interface Criterion {
    public enum Operator {
        EQ, NE, LIKE, GT, LT, GTE, LTE, AND, OR
    }

    public Predicate toPredicate(Root<?> root, CriteriaQuery<?> query,
                                 CriteriaBuilder builder);
}

创建一个自定义的Sepcification，添加add方法用来添加多个条件

import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;
import java.util.ArrayList;
import java.util.List;

/** * Created by 定义一个查询条件容器 on 17/6/6. */
public class Criteria<T> implements Specification<T> {
    private List<Criterion> criterions = new ArrayList<>();

    @Override
    public Predicate toPredicate(Root<T> root, CriteriaQuery<?> query,
                                 CriteriaBuilder builder) {
        if (!criterions.isEmpty()) {
            List<Predicate> predicates = new ArrayList<>();
            for (Criterion c : criterions) {
                predicates.add(c.toPredicate(root, query, builder));
            }
            // 将所有条件用 and 联合起来
            if (predicates.size() > 0) {
                return builder.and(predicates.toArray(new Predicate[predicates.size()]));
            }
        }
        return builder.conjunction();
    }

    /** * 增加简单条件表达式 * * @Methods Name add * @Create In 2012-2-8 By lee */
    public void add(Criterion criterion) {
        if (criterion != null) {
            criterions.add(criterion);
        }
    }
}

二：创建条件表达式接口的不同实现类

import org.springframework.util.StringUtils;

import javax.persistence.criteria.*;

/** * 简单条件表达式 * * @author lee */
public class SimpleExpression implements Criterion {

    private String fieldName;        //属性名
    private Object value;            //对应值
    private Operator operator;        //计算符

    protected SimpleExpression(String fieldName, Object value, Operator operator) {
        this.fieldName = fieldName;
        this.value = value;
        this.operator = operator;
    }

    public String getFieldName() {
        return fieldName;
    }

    public Object getValue() {
        return value;
    }

    public Operator getOperator() {
        return operator;
    }

    @SuppressWarnings({"rawtypes", "unchecked"})
    public Predicate toPredicate(Root<?> root, CriteriaQuery<?> query,
                                 CriteriaBuilder builder) {
        Path expression = null;
        if (fieldName.contains(".")) {
            String[] names = StringUtils.split(fieldName, ".");
            expression = root.get(names[0]);
            for (int i = 1; i < names.length; i++) {
                expression = expression.get(names[i]);
            }
        } else {
            expression = root.get(fieldName);
        }

        switch (operator) {
            case EQ:
                return builder.equal(expression, value);
            case NE:
                return builder.notEqual(expression, value);
            case LIKE:
                return builder.like((Expression<String>) expression, "%" + value + "%");
            case LT:
                return builder.lessThan(expression, (Comparable) value);
            case GT:
                return builder.greaterThan(expression, (Comparable) value);
            case LTE:
                return builder.lessThanOrEqualTo(expression, (Comparable) value);
            case GTE:
                return builder.greaterThanOrEqualTo(expression, (Comparable) value);
            default:
                return null;
        }
    }

}

import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;
import java.util.ArrayList;
import java.util.List;

/** * 逻辑条件表达式 用于复杂条件时使用，如单属性多对应值的OR查询等 * * @author lee */
public class LogicalExpression implements Criterion {
    private Criterion[] criterion;    // 逻辑表达式中包含的表达式
    private Operator operator;        //计算符

    public LogicalExpression(Criterion[] criterions, Operator operator) {
        this.criterion = criterions;
        this.operator = operator;
    }

    public Predicate toPredicate(Root<?> root, CriteriaQuery<?> query,
                                 CriteriaBuilder builder) {
        List<Predicate> predicates = new ArrayList<>();
        for (int i = 0; i < this.criterion.length; i++) {
            predicates.add(this.criterion[i].toPredicate(root, query, builder));
        }
        switch (operator) {
            case OR:
                return builder.or(predicates.toArray(new Predicate[predicates.size()]));
            default:
                return null;
        }
    }

}

这两个类分别模拟不同的条件查询。

三：创建一个工厂类，根据条件创建不同的实现类

import com.example.dynamic.Criterion.Operator;
import org.springframework.util.StringUtils;

import java.util.Collection;

/** * 条件构造器 * 用于创建条件表达式 * * @Class Name Restrictions * @Author lee */
public class Restrictions {

    /** * 等于 */
    public static SimpleExpression eq(String fieldName, Object value, boolean ignoreNull) {
        if (ignoreNull && StringUtils.isEmpty(value)) return null;
        return new SimpleExpression(fieldName, value, Operator.EQ);
    }

    /** * 不等于 */
    public static SimpleExpression ne(String fieldName, Object value, boolean ignoreNull) {
        if (ignoreNull && StringUtils.isEmpty(value)) return null;
        return new SimpleExpression(fieldName, value, Operator.NE);
    }

    /** * 模糊匹配 */
    public static SimpleExpression like(String fieldName, String value, boolean ignoreNull) {
        if (ignoreNull && StringUtils.isEmpty(value)) return null;
        return new SimpleExpression(fieldName, value, Operator.LIKE);
    }

    /** */
// public static SimpleExpression like(String fieldName, String value,
// MatchMode matchMode, boolean ignoreNull) {
// if (StringUtils.isEmpty(value)) return null;
// return null;
// }

    /** * 大于 */
    public static SimpleExpression gt(String fieldName, Object value, boolean ignoreNull) {
        if (ignoreNull && StringUtils.isEmpty(value)) return null;
        return new SimpleExpression(fieldName, value, Operator.GT);
    }

    /** * 小于 */
    public static SimpleExpression lt(String fieldName, Object value, boolean ignoreNull) {
        if (ignoreNull && StringUtils.isEmpty(value)) return null;
        return new SimpleExpression(fieldName, value, Operator.LT);
    }

    /** * 小于等于 */
    public static SimpleExpression lte(String fieldName, Object value, boolean ignoreNull) {
        if (ignoreNull && StringUtils.isEmpty(value)) return null;
        return new SimpleExpression(fieldName, value, Operator.GTE);
    }

    /** * 大于等于 */
    public static SimpleExpression gte(String fieldName, Object value, boolean ignoreNull) {
        if (ignoreNull && StringUtils.isEmpty(value)) return null;
        return new SimpleExpression(fieldName, value, Operator.LTE);
    }

    /** * 并且 */
    public static LogicalExpression and(Criterion... criterions) {
        return new LogicalExpression(criterions, Operator.AND);
    }

    /** * 或者 */
    public static LogicalExpression or(Criterion... criterions) {
        return new LogicalExpression(criterions, Operator.OR);
    }

    /** * 包含于 */
    @SuppressWarnings("rawtypes")
    public static LogicalExpression in(String fieldName, Collection value, boolean ignoreNull) {
        if (ignoreNull && (value == null || value.isEmpty())) {
            return null;
        }
        SimpleExpression[] ses = new SimpleExpression[value.size()];
        int i = 0;
        for (Object obj : value) {
            ses[i] = new SimpleExpression(fieldName, obj, Operator.EQ);
            i++;
        }
        return new LogicalExpression(ses, Operator.OR);
    }
}

四：使用

假设有个Post的entity，有title，content，count，url等参数，再创建一个PostRepository extends JpaRepository

    @Test
    public void contextLoads() {
        Criteria<Post> criteria = new Criteria<>();
        criteria.add(Restrictions.like("title", "1", true));
        criteria.add(Restrictions.eq("content", "content1", true));

        List<Post> postList = postRepository.findAll(criteria);
        for (Post post : postList) {
            System.out.println(post);
        }
    }

这里就可以比较优雅的创建不同的条件，然后拼接起来查询即可。相比之下要比原生的写法如

    studentInfoDao.findAll(new Specification<StudentInfo> () {  

   public Predicate toPredicate(Root<StudentInfo> root,  
     CriteriaQuery<?> query, CriteriaBuilder cb) {  
    Path<String> namePath = root.get("name");  
    Path<String> nicknamePath = root.get("nickname");  
    /** * 连接查询条件, 不定参数，可以连接0..N个查询条件 */  
    query.where(cb.like(namePath, "%李%"), cb.like(nicknamePath, "%王%")); //这里可以设置任意条查询条件 

    return null;  
   }  

  }, page);  

 }  

比这种写法好看一点。