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  • 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

    1 jdbc.drivers=com.microsoft.jdbc.sqlserver.SQLServerDriver
    2 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

    1 jdbc.drivers=com.microsoft.sqlserver.jdbc.SQLServerDriver
    2 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。

     1 public <T> List<T> executeQuery(final String sqlString, Integer current, Integer maxResult, Integer fetchSize, Class<T> t, Object... parameters) throws SqlExecutionException {
     2         List<T> rowsList;
     3         Session session = sessionLocal.get();
     4         try {
     5             Query query = session.createSQLQuery(sqlString);
     6             if (current != null) {
     7                 query.setFirstResult(current);
     8             }
     9 
    10             if (maxResult != null && maxResult > 0) {
    11                 query = query.setMaxResults(maxResult);
    12             }
    13 
    14             if (fetchSize != null && fetchSize > 0) {
    15                 query = query.setFetchSize(fetchSize);
    16             }
    17 
    18             if (parameters != null && parameters.length > 0) {
    19                 for (int i = 0; i < parameters.length; i++) {
    20                     query.setParameter(i, parameters[i]);
    21                 }
    22             }
    23 
    24             rowsList = query.setResultTransformer(Transformers.aliasToBean(t)).list();
    25         } catch (Exception e) {
    26             throw new SqlExecutionException(sqlString, e.getCause());
    27         } finally {
    28             session.close();
    29             session = null;
    30             sessionLocal.remove();
    31         }
    32         return rowsList;
    33     }

    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:

    1 List<HashMap> data = session.executeQuery(
    2                 "select * from test",
    3                 0,
    4                 100,
    5                 100,
    6                 HashMap.class,
    7                 null
    8         );

    则会抛出异常:

    1 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。

     1     protected SqlStatementWrapper executeQueryStatement(
     2             String sqlStatement,
     3             QueryParameters queryParameters,
     4             boolean scroll,
     5             List<AfterLoadAction> afterLoadActions,
     6             SessionImplementor session) throws SQLException {
     7 
     8         // Processing query filters.
     9         queryParameters.processFilters( sqlStatement, session );
    10 
    11         // Applying LIMIT clause.
    12         final LimitHandler limitHandler = getLimitHandler(
    13                 queryParameters.getRowSelection()
    14         );
    15         String sql = limitHandler.processSql( queryParameters.getFilteredSQL(), queryParameters.getRowSelection() );
    16 
    17         // Adding locks and comments.
    18         sql = preprocessSQL( sql, queryParameters, getFactory().getDialect(), afterLoadActions );
    19 
    20         final PreparedStatement st = prepareQueryStatement( sql, queryParameters, limitHandler, scroll, session );
    21         return new SqlStatementWrapper(
    22                 st, getResultSet(
    23                 st,
    24                 queryParameters.getRowSelection(),
    25                 limitHandler,
    26                 queryParameters.hasAutoDiscoverScalarTypes(),
    27                 session
    28         )
    29         );
    30     }

    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;

     1 @Override
     2     public String processSql(String sql, RowSelection selection) {
     3         if (LimitHelper.hasFirstRow( selection )) {
     4             throw new UnsupportedOperationException( "query result offset is not supported" );
     5         }
     6 
     7         final int selectIndex = sql.toLowerCase(Locale.ROOT).indexOf( "select" );
     8         final int selectDistinctIndex = sql.toLowerCase(Locale.ROOT).indexOf( "select distinct" );
     9         final int insertionPoint = selectIndex + (selectDistinctIndex == selectIndex ? 15 : 6);
    10 
    11         return new StringBuilder( sql.length() + 8 )
    12                 .append( sql )
    13                 .insert( insertionPoint, " TOP ? " )
    14                 .toString();
    15     }

    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。

     1 public class SQLServer2000Dialect extends SQLServerDialect {
     2 
     3     public SQLServer2000Dialect() {
     4         super();
     5     }
     6 
     7     @Override
     8     public LimitHandler getLimitHandler() {
     9         return new SQLServer2000LimitHandler(false, false);
    10     }
    11 }

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

     1 public class SQLServer2000LimitHandler  extends TopLimitHandler {
     2     public SQLServer2000LimitHandler(boolean supportsVariableLimit, boolean bindLimitParametersFirst) {
     3         super(supportsVariableLimit, bindLimitParametersFirst);
     4     }
     5 
     6     @Override
     7     public boolean supportsLimit() {
     8         return false;
     9     }
    10 }

    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

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  • 原文地址:https://www.cnblogs.com/braska/p/10483002.html
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