private void pagination(Invocation invocation, StatementHandler target) throws SQLException {
final MetaObject metaStatementHandler = getMetaObject(target);
final BoundSql boundSql = target.getBoundSql();
Page<?> page = PAGE_THREAD_LOCAL.get();
if (page == null) {
page = findPageParameter(boundSql.getParameterObject());
}
// 如果传入的参数中有分页对象且sql语句中有select，才做分页处理
String sql = boundSql.getSql().toLowerCase();
if (sql.startsWith("select") && page != null) {
// 采用物理分页后，就不需要mybatis的内存分页了，所以重置下面的两个参数
metaStatementHandler.setValue("delegate.rowBounds.offset", RowBounds.NO_ROW_OFFSET);
metaStatementHandler.setValue("delegate.rowBounds.limit", RowBounds.NO_ROW_LIMIT);
// 设置分页对象里的总记录数和总页数
Connection connection = (Connection) invocation.getArgs()[0];
MappedStatement mappedStatement =
(MappedStatement) metaStatementHandler.getValue("delegate.mappedStatement");
if (page.isCountTotal()) {
int recordsTotal = getTotalCount(sql, connection, mappedStatement, boundSql);
page.setTotalNum(recordsTotal);
}
// 最后重写sql
String pageSql = buildPageSql(sql, page);
metaStatementHandler.setValue("delegate.boundSql.sql", pageSql);
}
}
/**
* 获取总记录数
*
* @param sql 原始sql语句
* @param conn
* @param ms
* @param boundSql
* @return
* @throws SQLException
*/
private int getTotalCount(String sql, Connection conn, MappedStatement ms, BoundSql boundSql)
throws SQLException {
int start = sql.indexOf("from");
if (start == -1) {
throw new RuntimeException("statement has no 'from' keyword");
}
int stop = sql.indexOf("order by");
if (stop == -1) {
stop = sql.length();
}
String countSql = "select count(0) " + sql.substring(start, stop);
BoundSql countBoundSql =
new BoundSql(
ms.getConfiguration(),
countSql,
boundSql.getParameterMappings(),
boundSql.getParameterObject());
ParameterHandler parameterHandler =
new DefaultParameterHandler(ms, boundSql.getParameterObject(), countBoundSql);
PreparedStatement stmt = null;
ResultSet rs = null;
int count = 0;
try {
stmt = conn.prepareStatement(countSql);
// 通过parameterHandler给PreparedStatement对象设置参数
parameterHandler.setParameters(stmt);
rs = stmt.executeQuery();
if (rs.next()) {
count = rs.getInt(1);
}
} finally {
CloseableUtil.closeQuietly(rs);
CloseableUtil.closeQuietly(stmt);
}
return count;
}