如何解决这个OutOfMemoryError：Java堆空间

Question

i have the following program which goes to database and gets the value, i have excuted the query also it gives me only 47 row but when i run the same program in console mode it gives me Exception in thread "main" java.lang.OutOfMemoryError: Java heap space

package com.common;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Timestamp;
import java.sql.Types;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;

import com.common.Query;

public class GetColumnValuesFromDifferentTypes {
@SuppressWarnings("unused")
public static void printColumns(String query){
    ABIDAO abidao = new ABIDAO();
    int numberOfColumns=0,columnType = 0;
    String columnValue = "", columnName = "";
    Map<String, String> headerMap = new LinkedHashMap<String, String>();
        Connection connection = abidao.getConnection();
        if (connection != null) {
            try {
                headerMap = getHeader(query);
                System.out.println("====================================================================");
                System.out.println("Header Map : "+headerMap);
                System.out.println("====================================================================");
                PreparedStatement reportTablePS = connection.prepareStatement(query);
                ResultSet reportTable_rst = reportTablePS.executeQuery();
                ResultSetMetaData reportTable_rsmd = reportTable_rst.getMetaData();
                numberOfColumns = reportTable_rsmd.getColumnCount();

                    int i =0;
                    while (reportTable_rst.next()) {
                            for (int columnIterator = 1; columnIterator <= numberOfColumns; columnIterator++) {
                                 columnValue = null;
                               columnName = reportTable_rsmd.getColumnName(columnIterator);
                               columnType = reportTable_rsmd.getColumnType(columnIterator);

                               if(columnType == Types.CHAR || columnType == Types.VARCHAR || columnType == Types.LONGVARCHAR)
                               {
                                   columnValue = reportTable_rst.getString(columnName);
                               }else if(columnType == Types.INTEGER || columnType == Types.BIGINT || columnType == Types.SMALLINT || columnType == Types.NUMERIC)
                               {
                                   long templong = reportTable_rst.getLong(columnName);
                                   if(!reportTable_rst.wasNull())
                                   {
                                       columnValue  = Long.toString(templong);
                                   }
                               }else if(columnType == Types.DECIMAL || columnType == Types.DOUBLE || columnType == Types.FLOAT || columnType == Types.REAL)
                               {
                                   double tempDouble1 = reportTable_rst.getDouble(columnName);
                                   if(!reportTable_rst.wasNull())
                                   {
                                       columnValue  = Double.toString(tempDouble1);
                                   }
                               } else if(columnType == Types.TIME || columnType == Types.TIMESTAMP || columnType == Types.DATE)
                               {
                                   Timestamp sqlTimeStamp = reportTable_rst.getTimestamp(columnName);
                                   if(!reportTable_rst.wasNull())
                                   {
                                       columnValue = sqlTimeStamp.toString();
                                   }
                               }
                               System.out.println("columnValue : "+columnValue);
                               System.out.println(",");

                            }
                            System.out.println("====================================================================");
                        }
            } catch (Exception ex) {
                ex.printStackTrace();
            }finally {
                try {
                    abidao.closeConnection(connection, null, null);
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        }
}
@SuppressWarnings({ "unused" })
public static  Map<String, String> getHeader(String query) {
    ABIDAO abidao = new ABIDAO();
    String columnName="";
    int numberOfColumns=0,rowCount=1;
    Map<String, String> headerNamesMap = new LinkedHashMap<String, String>();
    Connection connection = abidao.getConnection();
    if (connection != null) {
        try {
            PreparedStatement reportTablePS = connection.prepareStatement(query);
            ResultSet reportTable_rst = reportTablePS.executeQuery();
            ResultSetMetaData rsmd = reportTable_rst.getMetaData();
            numberOfColumns = rsmd.getColumnCount();
            headerNamesMap.put("SNO","SNO");
              while (reportTable_rst.next()) {
                for (int i = 1; i <= numberOfColumns; i++) {
                  columnName = rsmd.getColumnName(i).toUpperCase();
                  if(!headerNamesMap.containsKey(columnName)){
                      headerNamesMap.put(columnName, columnName); 
                  }
                }
                rowCount++;
              }

        } catch (Exception ex) {
            ex.printStackTrace();
        }finally {
            try {
                abidao.closeConnection(connection, null, null);
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    }
    return headerNamesMap;
}
@SuppressWarnings("rawtypes")
public static void main(String[] args) {
    String query = "";
    Map dynamicQueryMap = new HashMap();
    Query queryObj = new Query();

    try {
        dynamicQueryMap = queryObj.getComplexReportQuery();
        if(dynamicQueryMap.containsKey("query")) query = dynamicQueryMap.get("query").toString();
    } catch (Exception ex) {
        ex.printStackTrace();
    }
    printColumns(query);

}
}

This is the query which is return from the Query method :

select
pi.po_number,poi.unit_cost,pi.placed_date CreateDate,
case when isnull(pi.date_closed) then pi.scheduled_arrival_date  
else pi.date_closed end as ReceviedDate,
poi.order_quantity,poi.roll_number,p.product_sku product_name,
pc.product_category_name,poi.rec_vendor_quantity,pv.vendor_name,p.et_conversion_unit_quantity,pi.note
from
purchase_order as pi,
purchase_order_inventory as poi,
product_vendors as pv,
products AS p,
product_categories AS pc
where
pi.purchase_order_id=poi.purchase_order_id and
pc.product_category_id=p.product_category_id and
poi.product_id = p.product_id and
poi.product_category_id=pc.product_category_id and
pi.vendor_id=pv.product_vendor_id and
( ( pi.date_closed  >= '2012-01-01' and pi.date_closed <='2012-09-05 23:59:59' ) 
or ( pi.scheduled_arrival_date  >= '2012-01-01' and pi.scheduled_arrival_date <='2012-09-05 23:59:59') ) and
pi.po_type=0 
and pi.status_id = 0 and  poi.transaction_type = 0  
order by pi.po_number ;

what is the problem here i am facing!! please help me to find it out.

Answer 1

You need to close all your resources, not just the connection. eg PreparedStatement.close() and ResultSet.close() If you don't do this they are retained and become a form of a memory leak.

I suggest you confirm this yourself using jmap -histo:live {pid} or using a memory profiler like VisualVM or YourKit.

Answer 2

You should close Connection but also ResultSet and Statements to avoid memory leaks.

And don't forget to close statements and other resources before using them again.

Statement stmt = ...;
...
stmt.close();
stmt = ...

Answer 3

After avoiding programatic errors to save more memory, you can try setting a specific heap size for your application by changing the configuration of your JVM. Take a look at this post: http://informix-zone.com/node/46

Answer 4

The heap size also depends on shared buffer defined in your database configuration file you have to increase your shared buffers size in database configuration files.

For monitoring heap you can use monitor tools:-

• jmap

• jmonitor