Question

我正在尝试使用Java jdbc连接从数据库中的相应源系统中检索表名，表中所有行的计数，最大更新时间戳。到目前为止，这就是我想出的。

Socket.io

public Map<String,Long> getGpTableCount() throws SQLException { List<String> gpTableList = getChunks(); // sourcedb.tablenamename,targetdb.tablename:SSN Iterator<String> keySetIterator_gpTableList = gpTableList.iterator(); // sourcedb.tablename,targetdb.tablename:SSN Connection sourcedbCon = (Connection) DbManager.getGpConnection(); PreparedStatement gp_pstmnt = null; String gpExcpnMsg; while(keySetIterator_gpTableList.hasNext()) { String gpTabSchemakey = keySetIterator_gpTableList.next(); // sourcedb.tablename,targetdb.tablename:SSN String[] tablesnSSNs = gpTabSchemakey.split(","); // tablesnSSNs[0]: sourcedb.tablename, tablesnSSNs[1]: targetdb.tablename:SSN String[] target = tablesnSSNs[1].split(":"); // target[0]=targetdb.tablename, target[1]=SSN String[] sourcedbTable = target[0].split("\\."); // sourcedbTable[0] = targetdb, sourcedbTable[1]=table String gpCountQuery = "select '" + sourcedbTable[1] + "' as TableName, count(*) as Count, source_system_name, max(xx_last_update_tms) from " + tablesnSSNs[0] + " where source_system_name = '" + target[1] + "' group by source_system_name"; System.out.println("\nGP Query: " + gpCountQuery); try { gp_pstmnt = sourcedbCon.prepareStatement(gpCountQuery); ResultSet gpCountRs = gp_pstmnt.executeQuery(); // gpCountRs(1): table, gpCountRs(2): count, gpCountRs(3): source_system_name, gpCountRs(4): max(xx_last_update_tms) while(gpCountRs.next()) { System.out.println("sourcedbTable[1]: " + sourcedbTable[1] + " gpCountRs.getString(3): " + gpCountRs.getString(3) + " gpCountRs.getLong(2): " + gpCountRs.getLong(2)); gpCountMap.put(sourcedbTable[1] + "," + gpCountRs.getString(3), gpCountRs.getLong(2)); // (tableName,ssn,12345678) } } catch(org.postgresql.util.PSQLException e) { System.out.println("In SQL Exception block"); gpExcpnMsg = e.getMessage(); gpTabNotFound.put(gpCountQuery, gpExcpnMsg + "\n"); } catch(SQLException e) { e.printStackTrace(); } catch(Exception e) { System.out.println("In Exception block"); gpExcpnMsg = e.getMessage(); e.printStackTrace(); } } System.out.println("GP Connection closed"); gp_pstmnt.close(); sourcedbCon.close(); return gpCountMap; }是一个arrayList，它从以下位置接收数组形式的数据：方法gpTableList 我在代码旁边的注释中细分了叙述者中存在的数据格式。这里的问题是，当我运行此方法时，我从表中获取了正确的数据，但它也立即产生了空指针异常。形成的查询，结果和异常消息如下所示：

getChunks()

异常对应的行：

GP Query: select 'xx_table_name' as TableName, count(*) as Count, source_system_name, max(xx_last_update_tms) from sourcedb.xx_table_name where source_system_name = 'ORACLE' group by source_system_name
sourcedbTable[1]: xx_table_name gpCountRs.getString(3): ORACLE gpCountRs.getLong(2): 5181260
In Exception block
Exception Message: null

java.lang.NullPointerException
        at com.recordcount.dao.ChunkData.getGpTableCount(ChunkData.java:117)
        at com.recordcount.entry.StartCount.main(StartCount.java:53)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.eclipse.jdt.internal.jarinjarloader.JarRsrcLoader.main(JarRsrcLoader.java:58)

这是我的主要课程：

gpCountMap.put(analyticsTable[1] + "," + gpCountRs.getString(3), gpCountRs.getLong(2));

我试图调试代码，但是我无法理解我的错误。谁能告诉我该如何解决？

Answer 1

根据您的代码，gpCountMap为空，您已将其设为全局变量，但未初始化。

为了解决该问题，只需在getGpTableCount

的开头添加以下代码

gpCountMap = new HashMap<String,Long>();

或将其添加到main方法中：

public static void main(String[] args) throws SQLException, IOException, AddressException, InterruptedException {
    ChunkData chData = new ChunkData();
    chData.getGpTableCount();
    gpCountMap = new HashMap<String,Long>();
}

从数据库检索数据时出现空指针异常

1 个答案: