java - 错误 SessionMap 无法转换为 java.util.HashMap

Question

我试图在 session 中存储我的 HashMap 值，然后我使用 JSP 检索它，但我收到一条错误消息

HTTP Status 500 - org.apache.struts2.dispatcher.SessionMap cannot be cast to java.util.HashMap

知道我为什么会收到该错误吗？

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，我想一个一个地显示循环值。所以我现在正在使用这段代码，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;
}

因为你假设 abc 是一个 HashMap，这是错误的。它实际上是一个 SessionMap(错误消息就是这么说的)。 SessionMap 没有扩展 HashMap，它扩展了 AbstractMap，而 AbstractMap 直接扩展了 Object。

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

基本上，当您实现 SessionAware 时，您假设 Map 将是一个 HashMap，这是绝对不能保证的，而且确实不是案例。

我建议你替换属性定义:

HashMap abc = new HashMap();

与:

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