Question

我有以下程序进入数据库并获取值，我已经执行了查询，它也只给了我47行，但是当我在控制台模式下运行相同的程序时，它给了我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);

}
}

这是从Query方法返回的查询：

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 ;

我面临的问题是什么!!请帮我找出来。

Answer 1

您需要关闭所有资源，而不仅仅是连接。例如PreparedStatement.close（）和ResultSet.close（）如果不这样做，它们将被保留并成为内存泄漏的一种形式。

我建议您使用jmap -histo:live {pid}或使用VisualVM或YourKit等内存分析器自行确认。

Answer 2

您应该关闭Connection以及ResultSet和Statements以避免内存泄漏。

在再次使用它们之前不要忘记关闭语句和其他资源。

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

Answer 3

在避免编程错误以节省更多内存之后，您可以尝试通过更改JVM的配置来为应用程序设置特定的堆大小。看一下这篇文章：http://informix-zone.com/node/46

Answer 4

堆大小还取决于数据库配置文件中定义的共享缓冲区您必须在数据库配置文件中增加共享缓冲区大小。

对于监控堆，您可以使用监控工具： -

JMAP
jmonitor

如何解决这个OutOfMemoryError：Java堆空间

4 个答案: