How to retrieve the elements of HashSet using Struts2 tag without using s:iterator

Question

How to retrieve the elements of HashSet using Struts2 tag without using s:iterator

1k views Asked by Vasanth Subramanian At 26 December 2016 at 10:38

I am using Struts2. Please help me in understanding how to retrieve the elements of HashSet using Struts2 tag without using Struts iterator tag.

struts.xml

<struts>
<constant name="struts.devMode" value="true" />

<package name="bundle" extends="struts-default" namespace="/">

  <action name="fetchPage">
        <interceptor-ref name="defaultStack" />
        <result name="success">/jsp/page.jsp</result>
  </action>

  <action name="process" 
        class="sample.action.Process" 
        method="execute">
        <interceptor-ref name="defaultStack" />
        <result name="success">/jsp/result.jsp</result>
  </action>

</package>  
</struts>

Process.java (Action Class)

package sample.action;

import java.util.HashSet;
import java.util.Set;

import sample.pojo.Customer;

import com.opensymphony.xwork2.ActionSupport;

public class Process extends ActionSupport 
{
    private Set<Customer> result = new HashSet<Customer>();

    public String execute() 
    {
        Customer cust1 = new Customer();
        cust1.setAge(59);
        cust1.setName("Subramanian");
        result.add(cust1);

        return SUCCESS;
    }

    public Set<Customer> getResult() {
        return result;
    }

    public void setResult(Set<Customer> result) {
        this.result = result;
    }
}

Cutomer.java - Pojo class

package sample.pojo;
public class Customer{

    String name;
    int age;

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }   
}

result.jsp - View

<!DOCTYPE html>
<html>
<head>
<%@ taglib prefix="s" uri="/struts-tags"%>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
<meta http-equiv="X-UA-Compatible" content="IE=8;" />
<title>Welcome Page</title>
</head>
<body>
Welcome!
 <s:textfield id="custName" value="%{result[0].name}"/>
</body>
</html>

With above code, I am not able to read HashSet object value in result.jsp page.

Original Q&A

There are 3 answers

Roman C On 26 December 2016 at 11:35

You can use () notation instead of []. The last is for List and array, or Map. So it's not applicable to Set.

<s:textfield id="custName" value="%{result(0).name}"/>

You should add id property to the element's type. The id is a default key to map through a collection.

public class Customer{
    Integer id;
    String name;
    int age;
//getter and setter
}

Initialize the id property along with others

Customer cust1 = new Customer();

cust1.setId(0);
cust1.setAge(59);
cust1.setName("Subramanian");
result.add(cust1);

You can learn more about type conversion in Indexing a collection by a property of that collection.

Also OGNL development guide for understanding Indexing.

Alireza Fattahi On 27 December 2016 at 12:28

If you want to keep the Set you can use

<s:property value="%{result.iterator.next.name}"/>

Or

Change the Set to List, the List has a get method which the set does not .

After that both below will work

<s:property value="%{result[0].name}"/>
<s:property value="%{result.get(0).name}"/>

**Aleksandr M** · Accepted Answer · 2016-12-27 20:07:15

How to retrieve the elements of HashSet using Struts2 tag without using <s:iterator>?

By using some OGNL magic called projection.

<s:textfield id="custName" value="%{result.{name}[0]}" />

The result.{name} will create a list from all name values in the result and the [0] will retrieve first element of that list.

Note that because you are using HashSet iteration order is not guaranteed. Use LinkedHashSet to achieve predictable iteration order.

TechQA.

How to retrieve the elements of HashSet using Struts2 tag without using s:iterator

struts.xml

Process.java (Action Class)

Cutomer.java - Pojo class

result.jsp - View

There are 3 answers

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