How to Export HTML to PDF, CSV, and Excel using Display Tag in JSP? Example

Display tag provides export options to export page into PDF, CSV, Excel, and XML in Java web application written using JSP, Servlet, Struts, or Spring MVC framework. Display tag is a tag library and you just need to use it in your JSP page to display tabular data or generate HTML tables dynamically. Earlier we have seen 10 display tag tips for getting most out of display tag and in this JSP Servlet tutorial we will see one display tag export issue, which prevents display tag export functionality to work properly. 

Display tag experience is considered good in various JSP interviews and some questions related to sorting, paging, both internal paging and external paging and exporting on display tag also appear as various J2EE and Servlet Interview questions.

In my opinion, after the JSTL core tag library, display tag is the most popular tag library and every Servlet and JSP developer should familiar with the display tag.

Display tag Export Example

In order to enable export functionality in the display tag, configure the display tag in JSP as shown below. I believe this is the easiest way to include export functionality in Java web applications.

<display:table uid="UserDetailsScreen" name="sessionScope.userList" defaultsort="1" defaultorder="ascending" pagesize="10"  export ="true" requestURI="/SpringTest/displaytag.jsp">
    <display:column property="userId" sortable="true" title="Employee ID" maxLength="25" />
    <display:column property="name" sortable="true" title="Real Name" maxLength="25" />
    <display:column property="email"  title="Email Address" maxLength="25" />
    <display:column property="phone"  title="Phone" maxLength="25" /> 
 
    <display:setProperty name="basic.empty.showtable" value="true" />
    <display:setProperty name="paging.banner.group_size" value="10" />
    <display:setProperty name="paging.banner.item_name" value="user" />
    <display:setProperty name="paging.banner.item_names" value="users" />
 
</display:table>

export="true" option  enable export functionality in displaytag. You also need to include corresponding libraries like :

displaytag-export-poi-1.2.jar , itext-1.3.jar, poi-3.2.jar etc. to export HTML table into Microsoft Excel, PDF , CSV and XML format. In next section we will see a common display tag export issue which can break export functionality in your Java web application.

Displaytag Export Issue

After enabling display tag export functionality, though it was working in the test program, export option on display tag for CSV, PDF, Excel, and XML was not working on the actual project. Display tag was throwing following error message when user clicks on the export button :

"Unable to reset response before returning exported data. You are not using an export filter. Be sure that no other jsp tags are used before display:table or refer to the displaytag documentation on how to configure the export filter"

Cause of Display tag export problem:

We are using Spring security for LDAP authentication and controlling concurrent active session in the Java web applications. Spring security framework uses filters to implement security features and has following filter declared in web.xml

<filter>
        <filter-name>springSecurityFilterChain</filter-name>
        <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
</filter>
<filter-mapping>
        <filter-name>springSecurityFilterChain</filter-name>
        <url-pattern>/*</url-pattern>
</filter-mapping>

I think you won't face this display tag export issue until you are using any filter in your web.xml file. As I haven't seen this before adding Spring security support in web application and the export option of displaytag was working even without this configuration.

How to fix Display tag export issue:

You can use the following steps to fix the display tag export issue in your Java web application :

1) Add ResponseOverrideFilter filter as shown below.

<filter>
        <filter-name>ResponseOverrideFilter</filter-name>
        <filter-class>org.displaytag.filter.ResponseOverrideFilter</filter-class>
</filter>
<filter-mapping>
       <filter-name>ResponseOverrideFilter</filter-name>
       <url-pattern>*.htm</url-pattern>
</filter-mapping>

Make sure your filter mapping is correct i.e. if your URL pattern is ending with *.jsp then use that or if you using Struts and your URL pattern is using *.do or *.action than specify accordingly. I was using the Spring MVC framework which uses ViewResolver design pattern to resolve view e.g. JSP and we have configured it to listen to .htm extension.

2) Make sure that the display tag's ResponseOverrideFilter must be first filter in web.xml

That’s all on How to fix the display tag export issue in the Java web application. As discussed in 10 display tag examples with JSP and Spring, the display tag is the easiest way to generate tables from JSP based web applications. It also the easiest way to enable export functionality which seamlessly allows user to export the table’s content into PDF, CSV, XML, and Microsoft Excel files. 

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