使用jdbc对数据库进行多次查询

Question

I have a text file from where i read values

FileInputStream file = new FileInputStream("C:/workspace/table_export.txt");
BufferedReader br = new BufferedReader(new InputStreamReader(file));
String line = null;
while( (line = br.readLine())!= null )
{
        String [] tokens = line.split("\\s+");
        String var_1 = tokens[0];
        System.out.println(var_1);
        getstaffinfo(var_1,connection);
}

The values read from text file is passed to getstaffinfo method to query the db

public static String getstaffinfo(String var_1, Connection connection) throws SQLException, Exception
  // Create a statement
   {
   StringBuffer query = new StringBuffer();
   ResultSet rs = null;
   String record = null;
   Statement stmt = connection.createStatement();
   query.delete(0, query.length());
   query.append("select firstname, middlename, lastname from users where employeeid = '"+var_1+"'");
   rs = stmt.executeQuery(query.toString());
       while(rs.next())
       {
   record = rs.getString(1) + " " +
                  rs.getString(2) + " " +
                  rs.getString(3);
  System.out.println(record);
 }
 return record;
}

I get almost 14000 values read from text file which is passed to getstaffinfo method, all database activities such has loading driver, establishing connectivity all works fine. But while printing

it throws error

java.sql.SQLException: ORA-00604: error occurred at recursive SQL level 1
ORA-01000: maximum open cursors exceeded
ORA-01000: maximum open cursors exceeded

Although i understand that this error is to do with database configuration, Is there an efficent way of making one db call and exceute the query for multiple values read from text file. Any inputs would be of great use.

Many Thanks in advance!!

Answer 1

Close ResultSet rs.close(); and Statement stmt.close(); after your while loop in getstaffinfo() , preferably inside a finally{}

Answer 2

You need to close resultSet via rs.close(); and Statement via stmt.close();

while(rs.next()){
   record = rs.getString(1) + " " +
            rs.getString(2) + " " +
            rs.getString(3);
   System.out.println(record);
}
rs.close();
stmt.close();

Answer 3

The issue is you are not close ing ResultSet and Statement (though it is good that your are working on one Connection ), try closing resources, the error should not happen.

Bigger issue is that if you do close, you are hitting DB n number of times where n is number of filtering criteria. One solution to this could be make in clause instead of = selection. eg:

Say total lines = N, divide into x chunks hence make N/x select statements

For example is N=20000, x=1000; you need to fire 20 selects instead of 20000.

Answer 4

以这种方式关闭结果集和语句

rs.close(); stmt.close();

Answer 5

Best way is to use IN clause in the query and call the method only once.

 FileInputStream file = new FileInputStream("C:/workspace/table_export.txt");
 BufferedReader br = new BufferedReader(new InputStreamReader(file));
 String line = null;
 String var_1 = "";
 while( (line = br.readLine())!= null )
 {
    String [] tokens = line.split("\\s+");
    var_1 = var_1+tokens[0]+",";
    System.out.println(var_1);
}
var_1 = var_1.subString(0,var_1.lastIndexOf(","));
getstaffinfo(var_1,connection);

change getstaffinfo() like this

public static List<String> getstaffinfo(String var_1, Connection connection) throws SQLException, Exception
// Create a statement
{
 StringBuffer query = new StringBuffer();
 ResultSet rs = null;
 String record = null;
 List<String> list = new ArrayList<String>();
 Statement stmt = connection.createStatement();
 query.delete(0, query.length());
 query.append("select firstname, middlename, lastname from users where employeeid IN ("+var_1+")");
 try{
  rs = stmt.executeQuery(query.toString());
   while(rs.next())
   {
     record = rs.getString(1) + " " +rs.getString(2) + " " +rs.getString(3);
     System.out.println(record);
     list.add(record);
    }
    }finally{
        stmt.close();
        rs.close();
    }
    return list;
 }

Note : Cant we put more than 1000 values in 'in clause'.
Related links.
1. https://forums.oracle.com/thread/235143?start=0&tstart=0
2. java.sql.SQLException: - ORA-01000: maximum open cursors exceeded