content: /**
   * Copyright &copy; 2012-2016 <a href="https://github.com/HuangBingGui/jeespring">jeespring</a> All rights reserved.
   */
  package com.jeespring.common.persistence.dialect;
  
  import com.jeespring.common.persistence.dialect.Dialect;
  
  /**
   * DB2的分页数据库方言实现
   *
   * @author poplar.yfyang
   * @version 1.0 2010-10-10 下午12:31
   * @since JDK 1.5
   */
  public class DB2Dialect implements Dialect {
      @Override
      public boolean supportsLimit() {
          return true;
      }
  
      private static String getRowNumber(String sql) {
          StringBuilder rownumber = new StringBuilder(50)
                  .append("rownumber() over(");
  
          int orderByIndex = sql.toLowerCase().indexOf("order by");
  
          if (orderByIndex > 0 && !hasDistinct(sql)) {
              rownumber.append(sql.substring(orderByIndex));
          }
  
          rownumber.append(") as rownumber_,");
  
          return rownumber.toString();
      }
  
      private static boolean hasDistinct(String sql) {
          return sql.toLowerCase().contains("select distinct");
      }
  
      @Override
      public String getLimitString(String sql, int offset, int limit) {
          return getLimitString(sql, offset, Integer.toString(offset), Integer.toString(limit));
      }
  
      /**
       * 将sql变成分页sql语句,提供将offset及limit使用占位符号(placeholder)替换.
       * <pre>
       * 如mysql
       * dialect.getLimitString("select * from user", 12, ":offset",0,":limit") 将返回
       * select * from user limit :offset,:limit
       * </pre>
       *
       * @param sql               实际SQL语句
       * @param offset            分页开始纪录条数
       * @param offsetPlaceholder 分页开始纪录条数－占位符号
       * @param limitPlaceholder  分页纪录条数占位符号
       * @return 包含占位符的分页sql
       */
      public String getLimitString(String sql, int offset, String offsetPlaceholder, String limitPlaceholder) {
          int startOfSelect = sql.toLowerCase().indexOf("select");
  
          StringBuilder pagingSelect = new StringBuilder(sql.length() + 100)
                  .append(sql.substring(0, startOfSelect)) //add the comment
                  .append("select * from ( select ") //nest the main query in an outer select
                  .append(getRowNumber(sql)); //add the rownnumber bit into the outer query select list
  
          if (hasDistinct(sql)) {
              pagingSelect.append(" row_.* from ( ") //add another (inner) nested select
                      .append(sql.substring(startOfSelect)) //add the main query
                      .append(" ) as row_"); //close off the inner nested select
          } else {
              pagingSelect.append(sql.substring(startOfSelect + 6)); //add the main query
          }
  
          pagingSelect.append(" ) as temp_ where rownumber_ ");
  
          //add the restriction to the outer select
          if (offset > 0) {
  //			int end = offset + limit;
              String endString = offsetPlaceholder + "+" + limitPlaceholder;
              pagingSelect.append("between ").append(offsetPlaceholder)
                      .append("+1 and ").append(endString);
          } else {
              pagingSelect.append("<= ").append(limitPlaceholder);
          }
  
          return pagingSelect.toString();
      }
  }
  