Question

我正在尝试将HashMap值存储在会话中，然后我使用JSP检索它但是我收到错误说

HTTP状态500 - org.apache.struts2.dispatcher.SessionMap无法强制转换为java.util.HashMap

知道我为什么会收到这个错误吗？

package com.action;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.text.BreakIterator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import com.action.GetCon;




public class JanuaryAction implements SessionAware{
private String name;
Map abc = new HashMap();


public Map getAbc() {
return abc;
}

public void setAbc(Map abc) {
this.abc = abc;
}


public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}

@Override
public void setSession(Map abc) {
this.abc = (HashMap) abc;

}
public String execute() throws Exception{

String time=getName();
 /*   System.out.println(time);*/
if(time.equals("January 2013")){

abc.put(time,"'2013-01-01' AND OrderDate <= '2013-01-31'" );
}
else if(time.equals("February 2013")){
abc.put(time,"'2013-02-01' AND OrderDate <='2013-02-31'" );
}
else if(time.equals("March 2013")){
abc.put(time,"'2013-03-01' AND OrderDate <='2013-03-31'" );
}
else if(time.equals("April 2013")){
abc.put(time,"'2013-04-01' AND OrderDate <='2013-04-31'" );
}
else if(time.equals("May 2013")){
abc.put(time,"'2013-05-01' AND OrderDate <='2013-05-31'" );
}
else if(time.equals("June 2013")){
abc.put(time,"'2013-06-01' AND OrderDate <='2013-06-05'" );
}
String newtime=(String)abc.get(time);
   /* System.out.println(newtime);*/

Connection con = GetCon.getCon();
Statement statement = con.createStatement();
ResultSet resultset = statement.executeQuery("SELECT MarketPlace,OrderDate, ROUND(SUM(Total),2),  COUNT(*) , ROUND(ROUND(SUM(Total),2)/ COUNT(*),2) FROM vend_printed WHERE OrderDate >=" +newtime+ " GROUP BY OrderDate,MarketPlace") ;
Object value = abc.remove(time);

while(resultset.next()){

String marketplace = resultset.getString(1);

String orderdate = resultset.getString(2);

Double datamount = resultset.getDouble(3);
Integer count= resultset.getInt(4);

Double result=resultset.getDouble(5);

abc.put(0, marketplace);
abc.put(1, orderdate);
abc.put(2, datamount);
abc.put(3, count);
abc.put(4, result);}

return "success";
}}

在我的JSP中，我想逐个显示循环值。所以我现在正在使用此代码，但它没有显示任何内容。

<s:property value="#session.0" /><br><br><br>
<s:property value="#session.1" /><br><br><br>
<s:property value="#session.2" /><br><br><br>
<s:property value="#session.3" /><br><br><br>
<s:property value="#session.4" /><br><br><br>

Answer 1

问题出在这里：

@Override
public void setSession(Map abc) {
  //abc is actually a SessionMap, which is not a HashMap !
  this.abc = (HashMap) abc;
}

因为您认为abc是HashMap，这是错误的。它实际上是SessionMap（这是错误消息所说的）。 SessionMap不会延伸HashMap，会延伸AbstractMap直接延伸Object。

请参阅：http://struts.apache.org/release/2.0.x/struts2-core/apidocs/org/apache/struts2/dispatcher/SessionMap.html

基本上，当您implements SessionAware时，您认为Map将是HashMap，这绝对不能保证，事实并非如此。

我建议你替换属性定义：

HashMap abc = new HashMap();

使用：

private Map abc; //Don't initialize it as it is done by the setter.

Answer 2

问题在于：

@Override
public void setSession(Map abc) {
    this.abc = (HashMap) abc;
}

您正在投射Map，这是HashMap的一个接口，这是一个具体的实现。此演员表不安全，因为您不确定abc是哪种类型。它可以是SessionMap，TreeMap，LinkedHashMap等中的任何一种。

由于setSession已被定义为Map，因此您应该使用Map或创建一个新的。{/ p>

public class JanuaryAction implements SessionAware{
    private String name;
    Map abc = new HashMap(); // Use the interface Map instead of a concrete implementation

    @Override
    public void setSession(Map abc) {
        // this.abc = abc; // you can do this
        this.abc = new HashMap(abc); // prefer to do this
    }
}

Answer 3

这是SessionAware实现，使用它

private Map<String, Object> session;

@Override
public void setSession(Map<String, Object> session) {
 this.session = session;
}

<{1>}在execute中创建一个包含值的新集合并放入会话映射中。您重复使用最初用于构建查询的同一变量abc的代码问题。您应该创建另一个并使用List而不是Map来保持要迭代并在JSP中显示的项目的顺序。最好创建和使用您应该从ResultSet填充的类，并将其填充到列表中。

public class Market {
  private String marketplace;  
  private String orderdate;  
  private Double datamount;
  private Integer count;  
  private Double result;

  public String getMarketplace() {
    return marketplace;
  }

  public void setMarketplace(String marketplace) {
    this.marketplace = marketplace;
  }

  public String getOrderdate() {
    return orderdate;
  }

  public void setOrderdate(String orderdate) {
    this.orderdate = orderdate;
  }

  public Double getDatamount() {
    return datamount;
  }

  public void setDatamount(Double datamount) {
    this.datamount = datamount;
  }

  public Integer getCount() {
    return count;
  }

  public void setCount(Integer count) {
    this.count = count;
  }

  public Double getResult() {
    return result;
  }

  public void setResult(Double result) {
    this.result = result;
  }

  public Market(String marketplace, String orderdate, Double datamount, Integer count, Double result) {
    this.marketplace = marketplace;
    this.orderdate = orderdate;
    this.datamount = datamount;
    this.count = count;
    this.result = result;
  }

}

创建属性以保存结果

@Element(value = Market.class)
private List<Market> markets = new ArrayList<>();

public List<Market> getMarkets() {
  return markets;
}

public void setMarkets(List<Market> markets) {
  this.markets = markets;
}

要填充列表，你应该使用这个块，我不知道你如何使用连接，所以我没有关闭它。

Connection con = GetCon.getCon();
Statement statement = con.createStatement();
try {
  ResultSet resultset = statement.executeQuery("SELECT MarketPlace,OrderDate, ROUND(SUM(Total),2),  COUNT(*) , ROUND(ROUND(SUM(Total),2)/ COUNT(*),2) FROM vend_printed WHERE OrderDate >=" +newtime+ " GROUP BY OrderDate,MarketPlace") ;
  while(resultset.next()){
  markets.add(new Market(
    resultset.getString(1),
    resultset.getString(2),
    resultset.getDouble(3),
    resultset.getInt(4),
    resultset.getDouble(5)
  ));
  }
} finally {
  try {
    statement.close();
  } catch (SQLException e) {}
}

}

现在将结果保存在会话中

session.put("markets", markets);

JSP中的

使用iterator标记，并且您不需要迭代会话对象，只需从操作中获取它。

<s:iterator value="markets">
  Marketplace: <s:property value="marketplace" /><br> 
  Orderdate: <s:property value="orderdate" /><br>  
  Datamount: <s:property value="datamount" /><br>
  Count: <s:property value="count" /><br>  
  Result: <s:property value="result" /><br>
  <hr>
</s:iterator>

错误SessionMap无法强制转换为java.util.HashMap

3 个答案: