• 查询语言：Query Language
• 条件表达式：where+having+on
• 输入参数：支持位置参数 ?1，和命名参数 :userName，但这两者不能混用
• 条件组合：属性导航：user.userName，一元运算 + -，逻辑操作 NOT AND OR，
  比较Comparison：= > >= < <= <>
  区间Between：[NOT] BETWEEN，支持数字、字符串、日期
  集合In：[NOT] IN，f in (‘a‘, ‘b‘) 等价于 f=‘a‘ or f=‘b‘
  相似Like：[NOT] LIKE，支持单个字符_、多个字符%、转义字符\_
  空值Null：IS [NOT] NULL，
  空集合：IS [NOT] EMPTY，select o from Order o where o.lineItems is empty，
  集合成员：[NOT] MEMBER OF，select p from Person p where ‘Joe‘ member of p.nicknames;
  存在性Exist：[NOT] EXISTS，select emp from Employee emp where exists ( select spouseEmp from Employee spouseEmp where spouseEmp = emp.spouse );//spouse配偶
  全部或任意：All+Any+Some，select emp from Employee where emp.salary > All { select m.salary from Manager m where m.department=emp.department };//部门高新员工
  子查询Subquery：select goodCustomer from Customer goodCustomer where goodCustomer.balanceOwed < ( select avg(c.balanceOwed)/2.0 from Customer c );//优质客户
• 原生标准操作
  字符串：concat，substr，trim，lower，
  算术：abs，sqrt，mod，size，index（select w.name from Course c join c.studentsWaitlist w where c.name=‘Calculus‘ and index(w)=0;）
  聚合：count，max，min，avg，sum，distinct
  日期：current_date，current_time，current_timestamp
  过程调用：select c from Customer c where function( ‘hasGoodCredit‘, c.balance, c.creditLimit );
  分支语句：update Employee e set e.salary = 
  case e.rating when 1 then e.salary*1.1
                        when 2 then e.salary*1.05
                        else e.salary*1.01
  end
  类型判断：select e from Employee e where type(e) in ( Exempt, Contractor )
• 分组和结果限定
  select c.status, avg(c.filledOrderCount), count(c) from Customer c group by c.status having c.status in ( 1, 2 );//统计状态1和2的客户信息
  select c, count(o) from Customer c Join c.orders o group by c having count(o) >= 5;//查询订单数大于等于5的客户
  
• 排序
  select o from Customer c JOIN c.orders o JOIN c.address a where a.state=‘CA‘ order by o.quantity DESC, o.totalcost;//总量倒序，花费升序
  
• 批量更新和删除
  delete from Customer c where c.status=‘inactive‘ and c.orders is empty;//删除未激活且没有订单的用户
  update Employee e set e.address.building=22 where e.address.building=14 and e.project=‘Java EE‘;//修改Java EE项目组成员的地址
  
• 查询条件：Criteria，标准条件
• CriteriaBuilder，@PersistenceUnit EntityManagerFactory.getCriteriaBuilder(); 或 @PersistenceContext EntityManager.getCriteriaBuilder();
  CriteriaQuery<T> createQuery(Class<T> resultClass);//创建查询，返回结果类型为resultClass
  CriteriaQuery<Tuple> createTupleQuery();//创建查询，返回元组类型，Tuple包含多个TupleElements
  CriteriaUpdate<T> createCriteriaUpdate(Class<T> targetEntity);//创建对targetEntity的批量修改操作
  CriteriaDelete<T> createCriteriaDelete(Class<T> targetEntity);//创建对targetEntity的批量删除操作
  CompoundSelection<Tuple> tuple(Selection<?>... selections);//创建tupe-valued查询
  CompoundSelection<Object[]> array(Selection<?>... selections);//创建array-valued查询
  Order asc(Expression<?> x);//创建表达式值的升序，desc为降序
  Expression<Double> avg(Expression<N> x);//计算平均值，还有count[Distinct]，sum，max+min（数字），greatest+least（字符串、日期等），
  Predicate exists(Subquery<?> subquery);//判断子查询是否存在，还有all，some，any，isTrue，isFalse，is[Not]Null
  Predicate and(Expression<Boolean> x, Expression<Boolean> y);//逻辑与，还有or，not
  Predicate or(Predicate... restrictions);//多个条件或，还有与and
  Predicate conjunction();//条件与，没有时返回true；还有disjunction，条件或，没有时返回false；
  Predicate equal(Expression<?> x, Expression<?> y);//判断是否相等，还有greaterThan[OrEqualTo]（Comparable），between，gt+ge+lt+le（Number）
  Predicate notEqual(Expression<?> x, Object value);//判断是否不等，还有lessThan[OrEqualTo]，like+notLike
  Expression<Number> sum(Expression<?> x, N y);//算术运算，还有neg+abs+prod积+diff差+quot商+mod模+sqrt平方根+concat+substring+trim+upper+length+locate
  Expression<Long> toLong(Expression<?> x);//类型转换，还有Integer+Float+Double+BigDecimal+BigInteger+String
  Expression<T> literal(T value);//转换常量值，
  Predicate is[Not]Empty(Expression<c> collection);//测试集合非空，还有size+is[Not]Member，q.where(cb.isEmpty(order.get("lineItems"))); => where order.lineItems is empty
  Expression<Collection<V>> values(M map);//从map的values()创建集合条件，还有keys
  Expression<java.sql.Date> currentDate();//当前日期，还有java.sql.Time=currentTime，java.sql.Timestamp=currentTimestamp
  In<T> in(Expression<T> expression);//q.having( cb.in( customer.get("status").value(1).value(2) ) ); => having c.status in ( 1,2 )
• CriteriaQuery -> AbstractQuery
  Root<X> from(Class<X> entityClass);//获得查询根，或与已有根计算笛卡尔积
  AbstractQuery<T> where(Predicate... restrictions);//限定条件（替换之间的条件）
  AbstractQuery<T> groupBy(Expression<?>... grouping);//分组，还有having+orderBy
  CriteriaQuery<T> select(Selection<?> selection);//设置选择结果
  CriteriaQuery<T> multiselect(Selection<?>... selections);//多个选择结果
  执行复杂条件查询
  @PersistenceContext EntityManager em;
  TypedQuery<T> query = em.createQuery(CriteriaQuery<T> cq);//创建查询对象
  query.setFirstResult().setMaxResults().getResultList();//获得查询结果
• CriteriaUpdate+CriteriaDelete，有from+where
  CriteriaUpdate<T> set(Path attribute, X value);//更新属性
  
  update customer c set c.status=‘outstanding‘ where c.balance<1000;
  CriteriaUpdaate<Customer> q=cb.createCriteriaUpdate(Customer.class);
  Root<Customer> c=q.from(Customer.class);
  q.set(c.get("status"), "outstanding")
  .where( cb.lt(c.get("balance"), 1000) );
• Root实体根+Join表连接 -> From查询 -> Path路径+Predicate与或 -> Expression表达式 -> Selection选择返回值
  Selection alias(String alias);//设置别名
  Predicate isNull();//是否空，还有isNotNull+
  Predicate in(Object... values);//集合元素，
  Path<Y> get(String attributeName);//获取路径
  Join join(String attributeName, JoinType type);//链接属性表，还有joinCollection，joinSet，joinList（t.index()限定多个对象的个数），joinMap（t.key()限定对象映射的key）
  Join on(Predicate... restrictions);//表链接
• 查询样例，最好先组织SQL和JPQL语句，然后再翻译为对象方法调用
• 获取全部或限定条件，select c from customer c where c.name="Jack";
  CriteriaQuery<Customer> q = CriteriaBuilder.createQuery(Customer.class);//返回类型为Customer
  Root<Customer> customer = q.from(Customer.class);//查询表Customer
  q.select(customer);//查询整个Customer对象
  q.where(cb.equal( customer.get("name"), ‘Jack‘));//限定name="Jack"的对象
• 连接统计，select s.name, count(p) from Supplier s left join s.products on p.status=‘inStock‘ group by s.name;
  CriteriaQuery<Tuple> q = cb.createTupleQuery();//配合后面的multiselect
  Root<Supplier> s = q.from(Supplier.class);//
  Join<Supplier, Product> p = s.join("products", JoinType.LEFT);//连接产品表
  p.on(cb.equal(p.get("status"), "inStock"));//限定连接条件，s.join("products", JoinType.LEFT).on(cb.equal(p.get("status"), "inStock"));
  q.groupBy( s.get("name") );
  q.multiselect( s.get("name"), cb.count(p) );//等价于q.select(cb.tuple(s.get("name"), cb.count(p)));，还有cb.array，cb.construct(Type.class, ... args)
• 深度获取fetch join，select d from Department d left join fetch d.employees where d.deptno=1;
  CriteriaQuery<Department> q = cb.createQuery(Department.class);
  Root<Department> d = q.from(Department.class);
  d.fetch("employees", JoinType.LEFT);//查询结果中d.employees有值
  q.where( cb.equal(d.get("deptno"), 1) );
  q.select(d);
• 路径导航，select p.vendor from Employee e join e.contactInfo.phones p where e.contactInfo.address.zipcode="95054";
  CriteriaQuery<Vendor> q = cb.createQuery<Vendor.class>;//返回结果为Vendor
  Root<Employee> e = q.from(Employee.class);//从Employee开始查询
  Join<ContactInfo, Phone> phone = e.join("contactInfo").join("phones");//连接多张表
  q.where( cb.equal(e.get("contactInfo").get("address").get("zipcode"), "95054") );
  q.select( phone.get("vendor") );
• 类型转换，select b.ISBN from Order o join treat(o.product AS Book) b;
  CriteriaQuery<String> q = cb.createQuery(String.class);
  Root<Order> order = q.from(Order.class);
  Join<Order, Book> book = cb.treat( order.join("product"), Book.class);
  q.select( book.get("isbn") );
• 分支查询，
  select e.name ,
  case when e.rating=1 then e.salary*1.1
          when e.rating=2 then e.salary*1.2
          else e.salary&1.01
  from Employee e where e.department.name=‘Engineering‘;
  CriteriaQuery<Tuple> q=cb.createTupleQuery();
  Root<Employee> e=q.from(Employee.class);
  q.where( cb.equal(e.get("department").get("name"), "Engineering") );
  q.multiselect( e.get("name"), cb.selectCase()
                                                       .when(cb.equal(e.get("rating"), 1), cb.prod(e.get("salary"), 1.1))
                                                       .when(cb.equal(e.get("rating"), 2), prod(e.get("salary"), 1.2))//这里需要常量的话调用cb.literal("value")
                                                       .otherWise(cb.prod(e.get("salary"), 1.01)) );
• 参数
  select c from Customer c where c.status = :stat;
  CriteriaQuery<Customer> q=cb.createQuery(Customer.class);
  Root<Customer> c=q.from(Customer.class);
  ParameterExpression<Integer> param=cb.parameter(Integer.class, "stat");
  q.select(c).where(cb.equal(c.get("status"), param));
• 子查询，select goodCustomer from Customer goodCustomer where goodCustomer.balanceOwed < ( select avg(c.balanceOwed) from Customer c );
  CriteriaQuery<Customer> q=cb.createQuery(Customer.class);
  Root<Customer> goodCustomer=q.from(Customer.class);
  Subquery<Double> sq=q.subquery(Double.class);//子查询返回double值
  Root<Customer> customer=sq.from(Customer.class);
  q.where(cb.lt(goodCustomer.get("balanceOwed"), sq.select(cb.avg(customer.get("balanceOwed")))));//goodCustomer.balanceOwed < avg(customer.balanceOwed)
  q.select(goodCustomer);
  
  select emp from Employee emp where emp.salary > all ( select m.salary from Manager m where m.department=emp.department );
  CriteriaQuery<Employee> q=cb.createQuery(Employee.class);
  Root<Employee> emp=q.from(Employee.class);
  Subquery<BigDecimal> sq=q.subquery(BigDecimal.class);
  Root<Manager> manager=sq.from(Manager.class);
  sq.select(manager.get("salary"));
  sq.where(cb.equals(manager.get("department"), emp.get("department")));
  q.select(emp).where(cb.gt(emp.get("salary"), cb.all(sq)));
• EntityManager
• 获得EntityManager
  @PersistenceContext EntityManager em;
  @PersistenceUnit EntityManagerFactory emf; emf.createEntityManager()//
  javax.persistence.Persistence.createEntityManagerFactory("order");//从persistence.xml文件读取unit配置
• 统计接口及实现：
  调用优先级Criteria API > Java Persistence Query Language > SQL
  有些统计语句可能是在很复杂只好执行原始的SQL语句了（sql条件需在可控范围内，最好检查一下参数安全性），但前两种在适当的时候还是应当多用的（防SQL注入）
  
  public class TongjiReposityImpl implements TongjiRepository {
      @PersistenceContext private EntityManager entityManager;
      @Override
      public CriteriaBuilder builder() {//Criteria API
          return entityManager.getCriteriaBuilder();
      }
      @Override
      public long count(CriteriaQuery<Long> query) {
          TypedQuery<Long> typedQuery = entityManager.createQuery(query);
          return typedQuery.getSingleResult();
      }
      @Override
      public Object[] sums(CriteriaQuery<Tuple> query) {
          List<Tuple> list = list(query, 0, 0);
          return list!=null && list.size()>0 ? list.get(0).toArray() : null;
      }
      @Override
      public List<Tuple> list(CriteriaQuery<Tuple> query, int firstResult, int maxResults) {
          TypedQuery<Tuple> typedQuery = entityManager.createQuery(query);
          typedQuery.setFirstResult(firstResult);
          if(maxResults>0) typedQuery.setMaxResults(maxResults);
          return typedQuery.getResultList();
      }
      @Override
      public int count(String jpql, Object... args) {//Java Persistence Query Language
          Query query = entityManager.createQuery(jpql);
          if(args!=null && args.length>0) {
              for(int i=0; i<args.length; i++) {
                  query.setParameter(i+1, args[i]);
              }
          }
          return ((Number)query.getSingleResult()).intValue();
      }
      @Override
      public Object[] sums(String jpql, Object... args) {
          List<?> list = list(jpql, args);
          if(list!=null && list.size()>0) {
              Object obj = list.get(0);
              if(obj instanceof Object[]) {
                  return (Object[])obj;
              }else {
                  return new Object[] {obj};
              }
          }
          return null;
      }
      @Override
      public List<?> list(String jpql, Object... args) {
          Query query = entityManager.createQuery(jpql);
          if(args!=null && args.length>0) {
              for(int i=0; i<args.length; i++) {
                  query.setParameter(i+1, args[i]);
              }
          }
          return query.getResultList();
      }
      @Override
      public int count(String sql) {//SQL
          Query query = entityManager.createNativeQuery(sql);
          return ((Number)query.getSingleResult()).intValue();
      }
      @Override
      public Object[] sums(String sql) {
          List<?> list = list(sql);
          if(list!=null && list.size()>0) {
              Object obj = list.get(0);
              if(obj instanceof Object[]) {
                  return (Object[])obj;
              }else {
                  return new Object[] {obj};
              }
          }
          return null;
      }
      @Override
      public List<?> list(String sql) {
          Query query = entityManager.createNativeQuery(sql);
          return query.getResultList();
      }
  }  
  
• sql辅助生成工具类
  
  /**
   * select column from table where condition group by column having condition order by column limit from,length
   */
  public class SqlBuilder {
      private String select;
      private String from;
      private StringBuilder where = new StringBuilder();
      private String groupBy;
      private String having;
      private String orderBy;
      private String limit;
      
      public static SqlBuilder builder() {
          return new SqlBuilder();
      }
      
      /**
       * @param select
       * <li>*
       * <li>column1,column2,...
       * <li>count(column1),sum(column2),avg(column3),...
       * <li>user.id,user.name,account.amount,...
       */
      public SqlBuilder select(String select) {
          this.select = select;
          return this;
      }
      
      /**
       * @param from
       * <li>ts_user
       * <li>ts_user u left join ts_account a on u.ts_user_id = a.ts_user_id
       * <li>jpql: TsUser user left join user.tsAccount account
       */
      public SqlBuilder from(String from) {
          this.from = from;
          return this;
      }
      
      /**
       * @param where
       * <li>null, to reset where
       * <li>name like ‘%Jack%‘
       * <li>id in (1,2,3)
       * <li>exists (select a.id from acount a where a.user_id=user.id)
       * <li>name is empty
       */
      public SqlBuilder where(String where) {
          if(StringUtils.isEmpty(where)) {
              this.where.setLength(0);
          }else {
              this.where.append(" and " + where);
          }
          return this;
      }
      
      /**
       * @param columnOperator
       * <li>column1 >=
       * <li>column2 !=
       */
      public SqlBuilder where(String columnOperator, Object value) {
          if(!StringUtils.isEmpty(value)) {
              where.append(" and " + columnOperator + " ‘" + sqlParam(value.toString()) + "‘");
          }
          return this;
      }
      
      public SqlBuilder groupBy(String groupBy) {
          this.groupBy = groupBy;
          return this;
      }
      
      public SqlBuilder having(String having) {
          this.having = having;
          return this;
      }
      
      public SqlBuilder orderBy(String orderBy) {
          this.orderBy = orderBy;
          return this;
      }
      
      /**
       * @param limit
       * <li>limit 0,10
       */
      public SqlBuilder limit(String limit) {
          this.limit = limit;
          return this;
      }
      
      public SqlBuilder eq(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              where.append(" and " + column + " = ‘" + sqlParam(value.toString()) + "‘");
          }
          return this;
      }
      
      public SqlBuilder ne(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              where.append(" and " + column + " != ‘" + sqlParam(value.toString()) + "‘");
          }
          return this;
      }
      
      public SqlBuilder like(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              where.append(" and " + column + " like ‘%" + sqlParam(value.toString()) + "%‘");
          }
          return this;
      }
      
      public SqlBuilder notLike(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              where.append(" and " + column + " not like ‘%" + sqlParam(value.toString()) + "%‘");
          }
          return this;
      }
      
      public SqlBuilder in(String column, Collection<?> value) {
          if(!CollectionUtils.isEmpty(value)) {
              where.append(" and " + column + " in (" + StringUtils.collectionToDelimitedString(value, ",", "‘", "‘") + ")");
          }
          return this;
      }
      
      public SqlBuilder notIn(String column, Collection<?> value) {
          if(!CollectionUtils.isEmpty(value)) {
              where.append(" and " + column + " not in (" + StringUtils.collectionToDelimitedString(value, ",", "‘", "‘") + ")");
          }
          return this;
      }
      
      public SqlBuilder gt(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              where.append(" and " + column + " > ‘" + sqlParam(value.toString()) + "‘");
          }
          return this;
      }
      
      public SqlBuilder gte(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              where.append(" and " + column + " >= ‘" + sqlParam(value.toString()) + "‘");
          }
          return this;
      }
      
      public SqlBuilder lt(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              where.append(" and " + column + " < ‘" + sqlParam(value.toString()) + "‘");
          }
          return this;
      }
      
      public SqlBuilder lte(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              where.append(" and " + column + " <= ‘" + sqlParam(value.toString()) + "‘");
          }
          return this;
      }
      
      public SqlBuilder between(String column, Object from, Object to) {
          if(StringUtils.isEmpty(from) && StringUtils.isEmpty(to)) return this;
          if(!StringUtils.isEmpty(from)) where.append(" and " + column + " >= ‘" + sqlParam(from.toString()) + "‘");
          else if(!StringUtils.isEmpty(to)) where.append(" and " + column + " <= ‘" + sqlParam(to.toString()) + "‘");
          else where.append(" and " + column + " between ‘" + sqlParam(from.toString()) + "‘ and ‘" + sqlParam(to.toString()) + "‘");
          return this;
      }
      
      public String sql() {
          if(select == null || from == null) //必须得有selece和from部分
              throw new RuntimeException("sql must contain select + from parts.");
          
          StringBuilder sql = new StringBuilder("select " + select+" from "+from);
          if(where.length() > 4) sql.append(" where " + where.substring(5));
          if(groupBy != null) sql.append(" group by " + groupBy);
          if(having != null) sql.append(" having " + having);
          if(orderBy != null) sql.append(" order by " + orderBy);
          if(limit != null) sql.append(" limit " + limit);
          return sql.toString();
      }
      //过滤掉引号‘"，逗号,分号;注释号--等sql敏感符号
      public static String sqlParam(String sqlParam) {
          return sqlParam.replaceAll("([‘;]+|(--)+)", "");
      }
  }
• jpql辅助工具类，与SqlBuilder类似
  
  public class JpqlBuilder {
      private String select;
      private String from;
      private StringBuilder where = new StringBuilder();
      private List<Object> args = new ArrayList<Object>();
      private String groupBy;
      private String having;
      private String orderBy;
      private String limit;
      
      public static JpqlBuilder builder() {
          return new JpqlBuilder();
      }
      
      /**
       * @param select
       * <li>*
       * <li>user.id,user.name,account.amount,...
       */
      public JpqlBuilder select(String select) {
          this.select = select;
          return this;
      }
      
      /**
       * @param from
       * <li>jpql: TsUser user left join user.tsAccount account
       */
      public JpqlBuilder from(String from) {
          this.from = from;
          return this;
      }
      
      /**
       * @param where
       * <li>null, to reset where
       * <li>name like ‘%Jack%‘
       */
      public JpqlBuilder where(String where) {
          if(StringUtils.isEmpty(where)) {
              this.where.setLength(0);
              args.clear();
          }else {
              this.where.append(" and " + where);
          }
          return this;
      }
      
      /**
       * @param columnOperator
       * <li>column1 >=
       * <li>column2 !=
       */
      public JpqlBuilder where(String columnOperator, Object value) {
          if(!StringUtils.isEmpty(value)) {
              args.add(value);
              where.append(" and " + columnOperator + " ?" + args.size());
          }
          return this;
      }
      
      public JpqlBuilder groupBy(String groupBy) {
          this.groupBy = groupBy;
          return this;
      }
      
      public JpqlBuilder having(String having) {
          this.having = having;
          return this;
      }
      
      public JpqlBuilder orderBy(String orderBy) {
          this.orderBy = orderBy;
          return this;
      }
      
      /**
       * @param limit
       * <li>limit 0,10
       */
      public JpqlBuilder limit(String limit) {
          this.limit = limit;
          return this;
      }
      
      public JpqlBuilder eq(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              args.add(value);
              where.append(" and " + column + " = ?" + args.size());
          }
          return this;
      }
      
      public JpqlBuilder ne(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              args.add(value);
              where.append(" and " + column + " != ?" + args.size());
          }
          return this;
      }
      
      public JpqlBuilder like(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              args.add(value);
              where.append(" and " + column + " like ?" + args.size());
          }
          return this;
      }
      
      public JpqlBuilder notLike(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              args.add(value);
              where.append(" and " + column + " not like ?" + args.size());
          }
          return this;
      }
      
      public JpqlBuilder in(String column, Collection<?> value) {
          if(!CollectionUtils.isEmpty(value)) {
              where.append(" and " + column + " in (");
              boolean first = true;
              for(Object obj : value) {
                  args.add(obj);
                  if(first) {
                      first = false;
                      where.append("?"+args.size());
                  }else {
                      where.append(" , ?"+args.size());
                  }
              }
              where.append(")");
          }
          return this;
      }
      
      public JpqlBuilder notIn(String column, Collection<?> value) {
          if(!CollectionUtils.isEmpty(value)) {
              where.append(" and " + column + " not in (");
              boolean first = true;
              for(Object obj : value) {
                  args.add(obj);
                  if(first) {
                      first = false;
                      where.append("?"+args.size());
                  }else {
                      where.append(" , ?"+args.size());
                  }
              }
              where.append(")");
          }
          return this;
      }
      
      public JpqlBuilder gt(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              args.add(value);
              where.append(" and " + column + " > ?" + args.size());
          }
          return this;
      }
      
      public JpqlBuilder gte(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              args.add(value);
              where.append(" and " + column + " >= ?" + args.size());
          }
          return this;
      }
      
      public JpqlBuilder lt(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              args.add(value);
              where.append(" and " + column + " < ?" + args.size());
          }
          return this;
      }
      
      public JpqlBuilder lte(String column, Object value) {
          if(!StringUtils.isEmpty(value)) {
              args.add(value);
              where.append(" and " + column + " <= ?" + args.size());
          }
          return this;
      }
      
      public JpqlBuilder between(String column, Object from, Object to) {
          if(StringUtils.isEmpty(from) && StringUtils.isEmpty(to)) return this;
          if(!StringUtils.isEmpty(from)) {
              args.add(from);
              where.append(" and " + column + " >= ?" + args.size());
          }else if(!StringUtils.isEmpty(to)) {
              args.add(to);
              where.append(" and " + column + " <= ?" + args.size());
          }else {
              args.add(from);
              args.add(to);
              where.append(" and " + column + " between ?" + (args.size()-1) + " and ?" + args.size());
          }
          return this;
      }
      
      public String jpql() {
          if(select == null || from == null) //必须得有selece和from部分
              throw new RuntimeException("sql must contain select + from parts.");
          
          StringBuilder sql = new StringBuilder("select " + select+" from "+from);
          if(where.length() > 4) sql.append(" where " + where.substring(5));
          if(groupBy != null) sql.append(" group by " + groupBy);
          if(having != null) sql.append(" having " + having);
          if(orderBy != null) sql.append(" order by " + orderBy);
          if(limit != null) sql.append(" limit " + limit);
          return sql.toString();
      }
      
      public Object[] args() {
          return args.toArray();
      }
  }  
  

JPA