我正在开发一个Java-Jdbc程序，它将获取数据库中存在的所有表的行数。为此，我提出了以下代码：
// Get the source(gp) count
public Map<String,Long> getGpTableCount() throws SQLException {
Map<String, String> gpTableMap = getScopeTableList(); // Key: Sourceschema.tablename, value: Destschema.tablename:sourcesystem1,sourcesystem2...sourcesystemn
Set<String> gpTableSet = gpTableMap.keySet(); // Gets the Source Table names - Schema.Tablename
gpCountMap = new HashMap<String, Long>();
Iterator<String> keySetIterator_gpTables = gpTableSet.iterator();
Connection gpAnalyticsCon = (Connection) DbManager.getGpConnection();
while(keySetIterator_gpTables.hasNext()) {
//getting source system names
String gpTabSchemakey = keySetIterator_gpTables.next();
String tablesnSSNs = gpTableMap.get(gpTabSchemakey);
String[] ssnArray = tablesnSSNs.split(":");
String sourceSystems = ssnArray[1];
System.out.println(sourceSystems);
if(sourceSystems.equals("No_SSNs_available") || sourceSystems == "No_SSNs_available") {
System.out.println("In the if condition");
gptableCountWithoutSsn = tblCountWithoutSsn(gpTabSchemakey, gpAnalyticsCon);
gpTabMapWoSsn.put(gpTabSchemakey, gptableCountWithoutSsn);
} else {
System.out.println("In the else condition");
//get the source system names
String inSourceSystems = "('" + sourceSystems.replace(",", "','") + "')";
String gpSchemaTableName = gpTabSchemakey;
String[] gpparts = gpSchemaTableName.split("\\."); // schema, tablename
String gpTable = gpparts[1];
String gpCountQuery = "select '" + gpTable + "' as TableName, count(*) as Count, source_system_name from " + gpSchemaTableName + " where source_system_name in " + inSourceSystems +" group by source_system_name order by source_system_name";
// resultSet(1): TableName, resultSet(2): count, resultSet(3): source_system_name
try {
PreparedStatement gp_pstmnt = gpAnalyticsCon.prepareStatement(gpCountQuery);
ResultSet gpCountRs = gp_pstmnt.executeQuery();
while(gpCountRs.next()) {
System.out.println("Tablename: " + gpCountRs.getString(1) + " Source System Name: " + gpCountRs.getString(3) + ", Count: " + gpCountRs.getLong(2));
System.out.println(" ");
ssn = getSsn(gpCountRs.getString(3));
gpCountMap.put(gpTable + ": " + gpCountRs.getString(3), gpCountRs.getLong(2));
}
} catch(org.postgresql.util.PSQLException e) {
System.out.println("Table: " + gpTable + " not found for the source system: " + ssn);
} catch(SQLException e) {
e.printStackTrace();
} catch(Exception e) {
e.printStackTrace();
}
}
}
gpAnalyticsCon.close();
return gpCountMap;
}
代码中有两种表。
有一个if-else条件，其中没有源系统名称的表转到'if'且那些有源系统，转到'else'条件。
在'if'中，我正在调用另一种方法：tblCountWithoutSsn，其编写为：
// Method that returns the row count of tables without any source system name
private Long tblCountWithoutSsn(String tableWithoutSsn, Connection con) throws SQLException {
String[] woSsn = tableWithoutSsn.split("\\.");
long count=0;
String tablename = woSsn[1];
String query = "select '" + tablename + "' as TableName, count(*) as count from " + tableWithoutSsn;
System.out.println("Executing table: " + tablename + " which doesn't have any source system name");
System.out.println("Query for tables with no source_systems: " + query);
PreparedStatement gpwoSsn_pstmnt = con.prepareStatement(query);
ResultSet rs = gpwoSsn_pstmnt.executeQuery();
while(rs.next()) {
count = rs.getLong(2);
}
System.out.println("TableName: " + tablename + ", count: " + count);
return count;
}
有41个表没有任何源系统。当我执行jar文件时，我可以看到表的计数：
In the if condition
Executing table: table1withoutSSN which doesn't have any source system name
Query for tables with no source_systems: select 'table1withoutSSN' as TableName, count(*) as count from analytics_view.table1withoutSSN
TableName: table1withoutSSN, count: 1764
In the if condition
Executing table: table2withoutSSN which doesn't have any source system name
Query for tables with no source_systems: select 'table2withoutSSN' as TableName, count(*) as count from ge_hr3.table2withoutSSN
TableName: table2withoutSSN, count: 473376
但是一旦它到达表：table3WithoutSSN代码给出异常并且连接关闭。例外情况如下：
In the if condition
Executing table: table3WithoutSSN which doesn't have any source system name
Query for tables with no source_systems: select 'table3WithoutSSN' as TableName, count(*) as count from custSchema.table3WithoutSSN
Exception in thread "main" java.lang.reflect.InvocationTargetException
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)
Caused by: org.postgresql.util.PSQLException: This connection has been closed.
at org.postgresql.jdbc.PgConnection.checkClosed(PgConnection.java:803)
at org.postgresql.jdbc.PgConnection.prepareStatement(PgConnection.java:1621)
at org.postgresql.jdbc.PgConnection.prepareStatement(PgConnection.java:415)
at com.recordcount.dao.GpHiveRecords.tblCountWithoutSsn(GpHiveRecords.java:156)
at com.recordcount.dao.GpHiveRecords.getGpTableCount(GpHiveRecords.java:72)
at com.recordcount.entry.StartCount.main(StartCount.java:12)
... 5 more
例外中的第156行是：
PreparedStatement gpwoSsn_pstmnt = con.prepareStatement(query); from the method: `tblCountWithoutSsn`
DBManager类中的连接方法：
private static Connection gpAnalyticsConnection = null; // Creating gp connection
public static Connection getGpConnection() {
try {
Class.forName("org.postgresql.Driver");
if(gpAnalyticsConnection == null) {
gpAnalyticsConnection = DriverManager.getConnection("hostname", "username", "password");
return gpAnalyticsConnection;
} else {
return gpAnalyticsConnection;
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
return null;
} catch (SQLException e) {
e.printStackTrace();
return null;
}
}
有谁能让我知道我在这里做的错误是什么，我该如何纠正呢。