1. 什么是hql
HQL是Hibernate Query Language的缩写2. hql和sql区别/异同
HQL SQL
类名/属性 表名/列名
区分大小写,关键字不区分大小写 不区分大小写
别名 别名
?，从下标0开始计算位置(hibernate5之后不支持) ?，从顺序1开始计算位置
:命名参数 不支持:命名参数
面向对象的查询语言 面向结构查询语言
基本功能演示：
package com.chenjiahao.five.test;import java.util.Arrays;import java.util.List;import java.util.Map;import org.hibernate.Session;import org.hibernate.Transaction;import org.hibernate.query.Query;import org.junit.After;import org.junit.Before;import org.junit.Test;import com.chenjiahao.four.entity.Book;import com.chenjiahao.two.util.SessionFactoryUtils;public class HqlTest { private Session session; private Transaction transaction; @Before public void before() { session = SessionFactoryUtils.openSession(); transaction = session.beginTransaction(); } @After public void after() { transaction.commit(); session.close(); } /** * 返回对象（多个）用实体类 */ @Test public void testList1() { Query query = session.createQuery("from Book"); List list = query.list(); for (Book b : list) { System.out.println(b); } } /** * 返回单个列段，用字符串就可以接受 */ @Test public void testList2() { Query query = session.createQuery("select b.bookName as ss from Book b"); List list = query.list(); for (String b : list) { System.out.println(b); } } /** * 查两个列段及以上，默认返回的是Object【】 * b.bookId, b.bookName */ @Test public void testList3() { Query query = session.createQuery("select b.bookId,b.bookName as ss from Book b"); List list = query.list(); for (Object[] b : list) { System.out.println(Arrays.toString(b)); } } /** * 注意map是函数，所以不区分大小写，返回的是map集合 * new Map(b.bookId as bid, b.bookName as bname) */ @Test public void testList4() { Query query = session.createQuery("select new mAp(b.bookId,b.bookName) from Book b"); List HQL通用分页查询：
工具类：PageBean(分页的实体类)
package com.chenjiahao.five.util;import java.util.Map;import javax.servlet.http.HttpServletRequest;/** * 分页工具类 * */public class PageBean { private int page = 1;// 页码 private int rows = 3;// 页大小 private int total = 0;// 总记录数 private boolean pagination = true;// 是否分页 // 获取前台向后台提交的所有参数 private Map parameterMap; // 获取上一次访问后台的url private String url; /** * 初始化pagebean * * @param req */ public void setRequest(HttpServletRequest req) { this.setPage(req.getParameter("page")); this.setRows(req.getParameter("rows")); // 只有jsp页面上填写pagination=false才是不分页 this.setPagination(!"fasle".equals(req.getParameter("pagination"))); this.setParameterMap(req.getParameterMap()); this.setUrl(req.getRequestURL().toString()); } public int getMaxPage() { return this.total % this.rows == 0 ? this.total / this.rows : this.total / this.rows + 1; } public int nextPage() { return this.page < this.getMaxPage() ? this.page + 1 : this.getMaxPage(); } public int previousPage() { return this.page > 1 ? this.page - 1 : 1; } public PageBean() { super(); } public int getPage() { return page; } public void setPage(int page) { this.page = page; } public void setPage(String page) { this.page = StringUtils.isBlank(page) ? this.page : Integer.valueOf(page); } public int getRows() { return rows; } public void setRows(int rows) { this.rows = rows; } public void setRows(String rows) { this.rows = StringUtils.isBlank(rows) ? this.rows : Integer.valueOf(rows); } public int getTotal() { return total; } public void setTotal(int total) { this.total = total; } public void setTotal(String total) { this.total = Integer.parseInt(total); } public boolean isPagination() { return pagination; } public void setPagination(boolean pagination) { this.pagination = pagination; } public Map getParameterMap() { return parameterMap; } public void setParameterMap(Map parameterMap) { this.parameterMap = parameterMap; } public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } /** * 获得起始记录的下标 * * @return */ public int getStartIndex() { return (this.page - 1) * this.rows; } @Override public String toString() { return "PageBean [page=" + page + ", rows=" + rows + ", total=" + total + ", pagination=" + pagination + ", parameterMap=" + parameterMap + ", url=" + url + "]"; }} 工具类：StringUtils:
package com.chenjiahao.five.util;public class StringUtils { // 私有的构造方法，保护此类不能在外部实例化 private StringUtils() { } /** * 如果字符串等于null或去空格后等于""，则返回true，否则返回false * * @param s * @return */ public static boolean isBlank(String s) { boolean b = false; if (null == s || s.trim().equals("")) { b = true; } return b; } /** * 如果字符串不等于null或去空格后不等于""，则返回true，否则返回false * * @param s * @return */ public static boolean isNotBlank(String s) { return !isBlank(s); }} BaseDao:
package com.chenjiahao.five.util;import java.util.Collection;import java.util.List;import java.util.Map;import java.util.Map.Entry;import java.util.Set;import org.hibernate.Session;import org.hibernate.query.Query;/** * 1.设置参数问题 * 2.分页代码重复的问题 * * getCountSql(sql) * select count(1) from (sql) t * * getCountHql(hql) * hql = " from Book where bookName like :bookName" * hql ="select * from new Book(bid,bookName) where bookName like :bookName" * * @author dell * */public class BaseDao { /** * 同用的参数设值方法 * @param map 参数键值对集合 * @param query 处理hql对象 */ public void setParam(Map map,Query query) { if(map !=null && map.size() > 0) { Object value = null; Set > entrySet = map.entrySet(); for (Entry entry : entrySet) { //有的时候它并不是单纯的字符串，可能是数组比如爱好，也可能是集合 value=entry.getValue(); if (value instanceof Object[]) { query.setParameterList(entry.getKey(), (Object[])value); }else if(value instanceof Collection) { query.setParameterList(entry.getKey(), (Collection)value); }else { query.setParameter(entry.getKey(), value); } } } } public String getCountHql(String hql) { // hql = " from Book where bookName like :bookName" // hql ="select * from new Book(bid,bookName) where bookName like :bookName" //截取from后面的hql语句 int index = hql.toUpperCase().indexOf("FROM"); return " select count(*) " + hql.substring(index); } /** * 同用查询方法 * @param session * @param map * @param hql * @param pageBean * @return */ public List executeQuery(Session session,Map map,String hql,PageBean pageBean) { List list=null; if(pageBean != null && pageBean.isPagination()) { String countHql = getCountHql(hql); Query createQuery = session.createQuery(countHql); this.setParam(map, createQuery); pageBean.setTotal(createQuery.getSingleResult().toString()); Query query = session.createQuery(hql); //给预定hql语句执行对象中的参数赋值，有多少赋值多少 this.setParam(map, query); // 设置分页起始记录下标 query.setFirstResult(pageBean.getStartIndex()); //设置分页返回的最大结果集 query.setMaxResults(pageBean.getRows()); list=query.list() ; }else { Query query = session.createQuery(hql); //给预定hql语句执行对象中的参数赋值，有多少赋值多少 this.setParam(map, query); list=query.list(); } return list; } } BookDao：
Bookdao继承Basedao
package com.chenjiahao.four.dao;import java.util.HashMap;import java.util.List;import java.util.Map;import org.hibernate.Hibernate;import org.hibernate.Session;import org.hibernate.Transaction;import org.hibernate.query.Query;import com.chenjiahao.five.util.BaseDao;import com.chenjiahao.five.util.PageBean;import com.chenjiahao.five.util.StringUtils;import com.chenjiahao.four.entity.Book;import com.chenjiahao.four.entity.Category;import com.chenjiahao.two.util.SessionFactoryUtils;public class BookDao extends BaseDao{public List list2(Book book , PageBean pageBean){ Session session = SessionFactoryUtils.openSession(); Transaction transaction = session.beginTransaction(); String bookName = book.getBookName(); Map map=new HashMap<>(); String hql="from Book where 1=1"; if (StringUtils.isNotBlank(bookName)) { hql += " and bookName like :bookName"; map.put("bookName",bookName); } List list=super.executeQuery(session, map, hql, pageBean); transaction.commit(); session.close(); return list; } } 测试：
@Test public void testList2() { Book book=new Book(); PageBean pageBean=new PageBean(); //查询页数 //pageBean.setPage(2); //不分页 pageBean.setPagination(false); //查询条件 //book.setBookName("%西%"); List list = this.bookDao.list2(book, pageBean); for (Book b : list) { System.out.println(b); } }