Hibernate5.1+Sqlserver2000分页查询

前几天改到一个bug：从MS SQLserver上面同步表结构并且采集数据写入其他库。然后用的核心技术是用的Hibernate。

其中bug出在SQLServer2000版本上。排查下来发现2000版本真的是一个让人头疼的数据库。

   驱动jar包不兼容；hibernate5.1分页查询也不能用。系统表也与其他版本的天差地别。

一、驱动问题

一开始上网查询，发现大家都推荐用JTDS驱动。但是JTDS貌似不能与官方的Hibernate兼容,需要使用第三方Hibernate。

不然Hibernate在建立连接时会抛出驱动不能转换的异常。因为要做其他版本兼容（代码不做大改动），

所以没换成jtds的驱动（net.sourceforge.jtds.jdbc.Driver）。

然后用了ms2000的三个驱动。测试通过。但是要注意区分驱动和数据库连接信息的写法

jdbc.drivers=com.microsoft.jdbc.sqlserver.SQLServerDriver
jdbc.url=jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=test

在查找分页问题时，偶然发现了一个更方便的方法。

资料链接：https://blog.csdn.net/hexin373/article/details/8260752

maven中央库里的sqljdbc4是不行的。这里我特地下载了 sqljdbc_3.0.1301.101_chs.tar.gz。

链接: https://pan.baidu.com/s/1CkZeHRYg5V-LxhhmVbGY8A 提取码: kwaj

用了这个jar以后，就可以把上面三个ms2000的jar包删掉了，而且驱动和数据库连接信息也可以和其他版本做统一。所以推荐这个方法

jdbc.drivers=com.microsoft.sqlserver.jdbc.SQLServerDriver
jdbc.url=jdbc:sqlserver://localhost:1433;DatabaseName=COREJAVA

二、系统表问题

ms2005版本以后系统表做了很多增删，比如：sys.extended_properties等。这些在ms2000都没有。

但是这个问题比较好改。

这边放出两段查询表结构的语句，不过语句还没来得及优化。

private static final String STRUCT_SQL_FORMAT = Joiner.on("
").join(Arrays.asList(
            "SELECT convert(varchar(100), h.TABLE_CATALOG) AS TABLE_CATALOG, ",
            "upper(convert(varchar(100), h.TABLE_NAME)) AS TABLE_NAME, ",
            "convert(varchar(100), h.TABLE_TYPE) AS TABLE_TYPE, ",
            "convert(varchar(100),  h.value ) AS TABLE_COMMENT, ",
            "upper(convert(varchar(100), a.name)) AS COLUMN_NAME,",
            "convert(varchar(100), b.name) AS COLUMN_TYPE,",
            "convert(varchar(100), COLUMNPROPERTY(a.id,a.name,'PRECISION')) AS COLUMN_LENGTH,",
            "convert(varchar(100), isnull(COLUMNPROPERTY(a.id,a.name,'Scale'),0)) AS NUM_SCALE,",
            "convert(varchar(100), case when exists(SELECT 1 FROM sysobjects where xtype='PK' and name in (SELECT name FROM sysindexes WHERE indid in( SELECT indid FROM sysindexkeys WHERE id = a.id AND colid=a.colid ))) then 'YES' else 'NO' end) AS IS_PRIMARYKEY, ",
            "convert(varchar(100), case when a.isnullable=1 then 'YES'else 'NO' end) AS IS_NULLABLE, ",
            "convert(varchar(100), isnull(g.[value],'')) AS COLUMN_COMMENT, ",
            "dc.definition COLUMN_DEFAULT",
            "FROM syscolumns a ",
            "left join systypes b on a.xusertype = b.xusertype ",
            "inner join sysobjects d on a.id=d.id and d.xtype='U' and d.name <> 'dtproperties' ",
            "left join sys.extended_properties g on a.id=g.major_id and a.colid=g.minor_id  ",
            "left join (",
            "  select a.TABLE_CATALOG, a.TABLE_NAME, a.TABLE_TYPE, b.value from information_schema.tables a ",
            "  left join sys.extended_properties b on b.major_id = OBJECT_ID(a.TABLE_NAME) and b.minor_id = 0 ",
            ") h on h.TABLE_NAME = d.name ",
            "LEFT JOIN sys.default_constraints dc ON d.id=dc.parent_object_id AND a.colid=dc.parent_column_id AND a.cdefault=dc.[object_id]",
            "order by d.name "
    ));

    private static final String STRUCT_SQL_FORMAT_FOR_2000 = Joiner.on("
").join(Arrays.asList(
            "select convert(varchar(100), h.TABLE_CATALOG) AS TABLE_CATALOG,  ",
            "upper(convert(varchar(100), h.TABLE_NAME)) AS TABLE_NAME, ",
            "convert(varchar(100), h.TABLE_TYPE) AS TABLE_TYPE,  ",
            "convert(varchar(100),  ta.TABLE_COMMENT ) AS TABLE_COMMENT,  ",
            "upper(convert(varchar(100), ta.NAME)) AS COLUMN_NAME, ",
            "convert(varchar(100), ta.COLUMN_TYPE) AS COLUMN_TYPE, ",
            "convert(varchar(100), ta.COLUMN_LENGTH) AS COLUMN_LENGTH, ",
            "convert(varchar(100), isnull(ta.NUM_SCALE,0)) AS NUM_SCALE, ",
            "convert(varchar(100), ta.IS_PRIMARYKEY) AS IS_PRIMARYKEY,  ",
            "convert(varchar(100), ta.IS_NULLABLE) AS IS_NULLABLE,  ",
            "convert(varchar(100), ta.COLUMN_COMMENT) AS COLUMN_COMMENT,  ",
            "convert(varchar(100), ta.COLUMN_DEFAULT) AS COLUMN_DEFAULT ",
            " FROM  ", "(SELECT ",
            " TABLE_NAME = d.name, ",
            " TABLE_COMMENT = isnull(f. VALUE, ''), ",
            " NAME = a.name, ",
            " IS_PRIMARYKEY = CASE WHEN EXISTS (SELECT 1 FROM sysobjects WHERE xtype = 'PK' AND parent_obj = a.id AND name IN ( SELECT name FROM sysindexes WHERE indid IN ( SELECT indid FROM sysindexkeys WHERE id = a.id AND colid = a.colid))) THEN 'YES' ELSE 'NO' END, ",
            " COLUMN_TYPE = b.name, ",
            " COLUMN_LENGTH = COLUMNPROPERTY(a.id, a.name, 'PRECISION'), ",
            " NUM_SCALE = isnull(COLUMNPROPERTY(a.id, a.name, 'Scale'), 0), ",
            " IS_NULLABLE = CASE WHEN a.isnullable = 1 THEN 'YES' ELSE 'NO' END, ",
            " COLUMN_DEFAULT = isnull(e. TEXT, ''), ",
            " COLUMN_COMMENT = isnull(g.[value], '') ",
            "FROM ", "	syscolumns a ",
            "LEFT JOIN systypes b ON a.xusertype = b.xusertype ",
            "INNER JOIN sysobjects d ON a.id = d.id AND d.xtype = 'U' AND d.name <> 'dtproperties' ",
            "LEFT JOIN syscomments e ON a.cdefault = e.id ",
            "LEFT JOIN sysproperties g ON a.id = g.id AND a.colid = g.smallid ",
            "LEFT JOIN sysproperties f ON d.id = f.id AND f.smallid = 0 ",
            ") ta ", "left join information_schema.tables h on h.TABLE_NAME = ta.table_name"
    ));

三、Hibernate5.1分页问题

最头疼的问题。我不懂是Hibernate官方根本没测试过ms2000的分页，还是我的用法有问题。

public <T> List<T> executeQuery(final String sqlString, Integer current, Integer maxResult, Integer fetchSize, Class<T> t, Object... parameters) throws SqlExecutionException {
        List<T> rowsList;
        Session session = sessionLocal.get();
        try {
            Query query = session.createSQLQuery(sqlString);
            if (current != null) {
                query.setFirstResult(current);
            }

            if (maxResult != null && maxResult > 0) {
                query = query.setMaxResults(maxResult);
            }

            if (fetchSize != null && fetchSize > 0) {
                query = query.setFetchSize(fetchSize);
            }

            if (parameters != null && parameters.length > 0) {
                for (int i = 0; i < parameters.length; i++) {
                    query.setParameter(i, parameters[i]);
                }
            }

            rowsList = query.setResultTransformer(Transformers.aliasToBean(t)).list();
        } catch (Exception e) {
            throw new SqlExecutionException(sqlString, e.getCause());
        } finally {
            session.close();
            session = null;
            sessionLocal.remove();
        }
        return rowsList;
    }

上面代码是我做的Hibernate分页封装。maxResult实际上相当于pageSize。如果maxResult为空则运行正常。但一旦指定了maxResult，就会报错。

调用上面方法：

List<HashMap> data = session.executeQuery(
                "select * from test",
                0,
                100,
                100,
                HashMap.class,
                null
        );

则会抛出异常：

com.syher.hibernate.jdbc.exception.SqlExecutionException: 第 1 行: '@P0' 附近有语法错误。

什么原因导致的？明明就一条简单的查询语句啊？

跟踪Hibernate源代码到Loader的executeQueryStatement方法。

    protected SqlStatementWrapper executeQueryStatement(
            String sqlStatement,
            QueryParameters queryParameters,
            boolean scroll,
            List<AfterLoadAction> afterLoadActions,
            SessionImplementor session) throws SQLException {

        // Processing query filters.
        queryParameters.processFilters( sqlStatement, session );

        // Applying LIMIT clause.
        final LimitHandler limitHandler = getLimitHandler(
                queryParameters.getRowSelection()
        );
        String sql = limitHandler.processSql( queryParameters.getFilteredSQL(), queryParameters.getRowSelection() );

        // Adding locks and comments.
        sql = preprocessSQL( sql, queryParameters, getFactory().getDialect(), afterLoadActions );

        final PreparedStatement st = prepareQueryStatement( sql, queryParameters, limitHandler, scroll, session );
        return new SqlStatementWrapper(
                st, getResultSet(
                st,
                queryParameters.getRowSelection(),
                limitHandler,
                queryParameters.hasAutoDiscoverScalarTypes(),
                session
        )
        );
    }

LimitHandler类是把我们的sql语句加工成分页语句的类。

在这里，我们的sql语句select * from test 经过limitHandler.processSql方法处理后，  会变成 select top ? * from test;

@Override
    public String processSql(String sql, RowSelection selection) {
        if (LimitHelper.hasFirstRow( selection )) {
            throw new UnsupportedOperationException( "query result offset is not supported" );
        }

        final int selectIndex = sql.toLowerCase(Locale.ROOT).indexOf( "select" );
        final int selectDistinctIndex = sql.toLowerCase(Locale.ROOT).indexOf( "select distinct" );
        final int insertionPoint = selectIndex + (selectDistinctIndex == selectIndex ? 15 : 6);

        return new StringBuilder( sql.length() + 8 )
                .append( sql )
                .insert( insertionPoint, " TOP ? " )
                .toString();
    }

上网查了一下，jdbc prepareStatement预编译不支持top ?的写法。然后我特地写了个jdbc的demo验证，发现问题也确实出在jdbc。

@Test
    public void run() {
        try {
            String sql = "SELECT TOP ?* FROM test";
            Connection conn = getJDBCConnection();
            PreparedStatement pst = conn.prepareStatement(sql);
            pst.setInt(1, 10);
            ResultSet rs = pst.executeQuery();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static Connection getJDBCConnection() throws IOException {
        Connection conn = null;
        String drivers = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
        //String drivers = "com.microsoft.jdbc.sqlserver.SQLServerDriver";
        String url = "jdbc:sqlserver://192.168.2.173:1433;DatabaseName=dbtest";
        //String url = "jdbc:microsoft:sqlserver://192.168.2.173:1433;DatabaseName=dbtest";
        //String url = "jdbc:sqlserver://192.168.3.104:1433;DatabaseName=testdb";
        String userName = "sa";
        String password = "sa@173";
        //String password = "sa@104";
        if (drivers != null) {
            try {
                Class.forName(drivers).newInstance();
                conn = DriverManager.getConnection(url, userName, password);

            } catch (Exception e) {
                e.printStackTrace();
                System.out.println("数据库连接失败");
            }
        } else {
            System.out.println("数据库驱动不存在");
        }
        return conn;
    }

上面demo里，ms2008、ms2016都不会有问题。而只有ms2000抛出了“@P0' 附近有语法错误。”的异常。

抓耳挠腮了两天之后，终于在一篇博客里面找到了灵感。

参考资料：https://gcy6164.iteye.com/blog/1160119

一开始看到这篇资料时，我是确实按着博客步骤改，结果没用。遂放弃。

然后某天在TopLimitHandler类中看到了博客中的supportsLimit方法，才恍然大悟。原来是自己改错了方向。

我没看过Hibernate3.2的源码，但是大致猜测Hibernate3.2中应该是没有LimitHandler类的。所以Hibernate3.2中判断

数据库是否支持分页是在SQLServerDialect中。而Hibernate5.1时为了更好的扩展，增加了LimitHandler专门处理分页语句的接口。

而判断数据库是否支持分页的方法也转移到了这个类中。

因此Hibernate3.2的修改教程不适合Hibernate5.1。但其实是同一个解决思路。

于是我自定义了一个Hibernate方言继承了SQLServerDialect，并重写了getLimitHandler方法。

public class SQLServer2000Dialect extends SQLServerDialect {

    public SQLServer2000Dialect() {
        super();
    }

    @Override
    public LimitHandler getLimitHandler() {
        return new SQLServer2000LimitHandler(false, false);
    }
}

自定义了SQLServer2000LimitHandler类，并修改了supportsLimit方法。

public class SQLServer2000LimitHandler  extends TopLimitHandler {
    public SQLServer2000LimitHandler(boolean supportsVariableLimit, boolean bindLimitParametersFirst) {
        super(supportsVariableLimit, bindLimitParametersFirst);
    }

    @Override
    public boolean supportsLimit() {
        return false;
    }
}

打包，调试。果然没问题了。

 我的hibernate测试代码：

https://github.com/rxiu/study-on-road/tree/master/trickle-hibernate