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;public interface Criterion {
enum Operator {
EQ, NE, LIKE, GT, LT, GTE, LTE, AND, OR, IS_MEMBER, IS_NOT_MEMBER
}
Predicate toPredicate(Root<?> root, CriteriaQuery<?> query,
CriteriaBuilder builder);}12345678910111213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);
}
}
}1234567891011121314151617181920212223242526272829303132333435363738394041二：创建条件表达式接口的不同实现类
import org.springframework.util.StringUtils;import javax.persistence.criteria.*;import java.util.List;import java.util.Map;import java.util.Set;/**
* 简单条件表达式
*
* @author lee
*/public class SimpleExpression implements Criterion {
/**
* 属性名
*/
private String fieldName; /**
* 对应值
*/
private Object value; /**
* 计算符
*/
private Operator operator; protected SimpleExpression(String fieldName, Object value, Operator operator) { this.fieldName = fieldName; this.value = value; this.operator = operator;
} @Override
@SuppressWarnings({"rawtypes", "unchecked"}) public Predicate toPredicate(Root<?> root, CriteriaQuery<?> query,
CriteriaBuilder builder) {
Path expression; //此处是表关联数据，注意仅限一层关联，如user.address，
//查询user的address集合中，address的name为某个值
if (fieldName.contains(".")) {
String[] names = StringUtils.split(fieldName, "."); //获取该属性的类型，Set？List？Map？
expression = root.get(names[0]);
Class clazz = expression.getJavaType(); if (clazz.equals(Set.class)) {
SetJoin setJoin = root.joinSet(names[0]);
expression = setJoin.get(names[1]);
} else if (clazz.equals(List.class)) {
ListJoin listJoin = root.joinList(names[0]);
expression = listJoin.get(names[1]);
} else if (clazz.equals(Map.class)) {
MapJoin mapJoin = root.joinMap(names[0]);
expression = mapJoin.get(names[1]);
} else { //是many to one时
expression = expression.get(names[1]);
}
} else { //单表查询
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); case IS_MEMBER: return builder.isMember(value, expression); case IS_NOT_MEMBER: return builder.isNotMember(value, expression); default: return null;
}
}
}123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990import 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 {
/**
* 逻辑表达式中包含的表达式
*/
private Criterion[] criterion; /**
* 计算符
*/
private Operator operator; public LogicalExpression(Criterion[] criterions, Operator operator) { this.criterion = criterions; this.operator = operator;
} @Override
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;
}
}
}12345678910111213141516171819202122232425262728293031323334353637383940414243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 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, Criterion.Operator.EQ);
} /**
* 集合包含某个元素
*/
public static SimpleExpression hasMember(String fieldName, Object value, boolean ignoreNull) { if (ignoreNull && StringUtils.isEmpty(value)) { return null;
} return new SimpleExpression(fieldName, value, Criterion.Operator.IS_MEMBER);
} /**
* 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, Criterion.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, Criterion.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, Criterion.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, Criterion.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, Criterion.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, Criterion.Operator.LTE);
} /**
* 并且
*/
public static LogicalExpression and(Criterion... criterions) { return new LogicalExpression(criterions, Criterion.Operator.AND);
} /**
* 或者
*/
public static LogicalExpression or(Criterion... criterions) { return new LogicalExpression(criterions, Criterion.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, Criterion.Operator.EQ);
i++;
} return new LogicalExpression(ses, Criterion.Operator.OR);
} /**
* 集合包含某几个元素，譬如可以查询User类中Set<String> set包含"ABC","bcd"的User集合，
* 或者查询User中Set<Address>的Address的name为"北京"的所有User集合
* 集合可以为基本类型或者JavaBean，可以是one to many或者是@ElementCollection
* @param fieldName
* 列名
* @param value
* 集合
* @return
* expresssion
*/
public static LogicalExpression hasMembers(String fieldName, Object... value) {
SimpleExpression[] ses = new SimpleExpression[value.length]; int i = 0; //集合中对象是基本类型，如Set<Long>，List<String>
Criterion.Operator operator = Criterion.Operator.IS_MEMBER; //集合中对象是JavaBean
if (fieldName.contains(".")) {
operator = Criterion.Operator.EQ;
} for (Object obj : value) {
ses[i] = new SimpleExpression(fieldName, obj, operator);
i++;
} return new LogicalExpression(ses, Criterion.Operator.OR);
}
}123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162四：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);
}
}123456789101112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);
} 123456789101112131415161718比这种写法好看一点。
版权声明：本文为博主武伟峰原创文章，转载请注明地址http://blog.csdn.net/tianyaleixiaowu。
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