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a fast small database connection pool and a active record flavor mini framework
package com.bixuebihui.jdbc;
/*
* @(#)SqlServer2000PageHepler.java 0.1 2009-12-30
* Copyright 2009 www.goldjetty.com Inc. All rights reserved.
*/
import com.bixuebihui.DbException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* SQL SERVER 2000 分页辅助类.
*
* @author xingwx
* @version 0.1
*/
public class SqlServer2000PageHelper {
SqlServer2000PageHelper() throws IllegalAccessException {
throw new IllegalAccessException("util class");
}
private static final String DESC = " desc";
/**
* 得到查询总数的SQL
*
* @param querySelect 查询SQL
* @return 得到总数的SQL
*/
public static String getCountString(String querySelect) {
querySelect = getLineText(querySelect);
int orderIndex = getLastOrderInsertPoint(querySelect);
int formIndex = getAfterFormInsertPoint(querySelect);
String select = querySelect.substring(0, formIndex);
//如果SELECT 中包含 group by 或者 distinct 就在外层包含COUNT
if (select.startsWith("select distinct") || isHaveGroupBy(querySelect)) {
return "select count(1) '_count' from (" +
querySelect.substring(0, orderIndex) + " ) _t";
}else {
return "select count (1) '_count' " +
querySelect.substring(formIndex, orderIndex);
}
}
/**
* 得到分页的SQL
* SELECT TOP 5 *
* FROM (SELECT TOP 10 *
* FROM table1
* ORDER BY id DESC) _table1
* ORDER BY id
*
* @param querySelect select语句
* @param offset 偏移量
* @param limit 限度
* @return 分页SQL
*/
public static String getLimitString(String querySelect, int offset, int limit) {
String innerQuerySelect = getLineText(querySelect);
if (offset > 0) {
int orderbyPos = getLastOrderInsertPoint(innerQuerySelect);
if (orderbyPos < 0) {
throw new UnsupportedOperationException("query result offset is not supported without 'order by' subclause");
} else {
String orderBy = innerQuerySelect.substring(orderbyPos);
String reverseOrderBy = "order by " + reversOrderbyClause(querySelect.substring(orderbyPos + "order by".length()));
String coreSql = innerQuerySelect.substring(0, orderbyPos);
StringBuilder sb = new StringBuilder(innerQuerySelect.length() * 2)
.append(coreSql)
.insert(getAfterSelectInsertPoint(coreSql), " top " + offset)
.append(reverseOrderBy);
sb.insert(0, "select top " + limit + " * from (").append(") _table1 ").append(orderBy);
return sb.toString();
}
}
return new StringBuilder(innerQuerySelect.length() + 8)
.append(innerQuerySelect)
.insert(getAfterSelectInsertPoint(innerQuerySelect), " top " + limit)
.toString();
}
/**
* 认为order by 子句为select语句的最后子句
* @param substring 颠倒排序字段
* @return 正序倒序翻转后的sql
*/
static String reversOrderbyClause(String substring) {
String [] arr = substring.split("\\,");
StringBuilder sb = new StringBuilder(substring.length()*2);
for (int i = 0; i < arr.length; i++) {
sb.append(toggleOrder(arr[i]));
if(i != arr.length-1) {
sb.append(",");
}
}
return sb.toString();
}
private static String toggleOrder(String ascdesc){
ascdesc = ascdesc.trim();
if(ascdesc.endsWith(DESC)) {
return ascdesc.substring(0, ascdesc.lastIndexOf(DESC));
} else if(ascdesc.endsWith(" asc")){
ascdesc = ascdesc.substring(0, ascdesc.lastIndexOf(" asc"));
}
return ascdesc+DESC;
}
private static int getAfterSelectInsertPoint(String sql) {
int selectIndex = sql.toLowerCase().indexOf( "select" );
final int selectDistinctIndex = sql.toLowerCase().indexOf( "select distinct" );
return selectIndex + ( selectDistinctIndex == selectIndex ? 15 : 6 );
}
/**
* 判断是否包含正确group by
* @return 如果包含返回True否则返回false
*/
private static boolean isHaveGroupBy(String querySelect){
int groupIndex = querySelect.toLowerCase().lastIndexOf("group by");
return (groupIndex != -1 && isBracketCanPartnership(querySelect.substring(groupIndex)));
}
/**
* 得到最后一个order By的插入点位置
* @return 返回最后一个order By插入点的位置
* @throws DbException 如果不存在正确的order by
*/
private static int getLastOrderInsertPoint(String querySelect) {
int orderIndex = querySelect.toLowerCase().lastIndexOf("order by");
if (orderIndex == -1
|| !isBracketCanPartnership(querySelect.substring(orderIndex))) {
throw new DbException("SQL 2000 分页必须要有Order by 语句!");
}
return orderIndex;
}
/**
* 将SQL语句变成一条不换行语句，并且每个单词的间隔都是1个空格
* @param text 需要转化的文本
* @return 如果sql是NULL返回空，否则返回转化后的SQL
*/
static String getLineText(String text) {
return text.replaceAll("[\r\n]", " ").replaceAll("\\s{2,}", " ");
}
/**
* 得到SQL第一个正确的FROM的的插入点
* @param querySelect 完整的查询语句
* @return 正确的FROM插入点
*/
private static int getAfterFormInsertPoint(String querySelect) {
String regex = "\\s+FROM\\s+";
Pattern pattern = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
Matcher matcher = pattern.matcher(querySelect);
while (matcher.find()) {
int fromStartIndex = matcher.start(0);
String text = querySelect.substring(0, fromStartIndex);
if (isBracketCanPartnership(text)) {
return fromStartIndex;
}
}
return 0;
}
/**
* 判断括号'()'是否匹配
* @param text 要判断的文本
* @return 如果匹配返回TRUE,否则返回FALSE
*/
static boolean isBracketCanPartnership(String text) {
return text != null
&& getIndexOfCount(text, '(') == getIndexOfCount(text, ')');
}
/**
* 得到一个字符在另一个字符串中出现的次数
* @param text 文本
* @param ch 字符
* @return 字符出现在文本的次数.
*/
private static int getIndexOfCount(String text, char ch) {
int count = 0;
for (int i = 0; i < text.length(); i++) {
count = (text.charAt(i) == ch) ? count + 1 : count;
}
return count;
}
}
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