Struts2, Tiles2, Spring, Hibernate, JQuery plugin - Linked Autocompleters

Disclaimer:
All the software applications that appear below represent trademarks and they are the property of their respective owners.
Use and implement my notes in this article at your own risk.

Discussion here:
1. General Considerations;
2. Prerequisites;
3. JQuery Autocompleters;
4. Linking autocompleters;
5. KeyValuePairBean;
6. Struts 2 Actions;
7. DAOs;
8. Annotated Hibernate entities;

1. General Considerations:
This sample is purposed to show how to link 3 JQuery autocompleters together; the 3 autocompleters will represent records from the tables "zone", "country", "city" of the "blog" database.
The sample will be presented somehow in a "top-down" fashion, ie. starting from View, then Controller, then Model components of the MVC web app architecture.

NOTE: if you don't know for example what is "blog" database, or other aspects, then you should read the "Struts2, Tiles2, Spring, Hibernate, JQuery plugin - General Considerations", which is used as a basis for this sample.

2. Prerequisites:
Make sure you have read the "Struts2, Tiles2, Spring, Hibernate, JQuery plugin - General Considerations", and installed and configured all that is written there;

3. JQuery Autocompleters:
The JQuery autocompleter refers to the "<sj:autocompleter />" object which is offered by the JQuery plugin taglib, namely "struts2-jquery-plugin-2.5.0.jar".
In order to use this plugin, you will have to include the following line in your JSP file:
<<
<%@ taglib prefix="sj" uri="/struts-jquery-tags"%>
>>
Thus, you made the JQuery autocompleter available to be used in your JSP file.

An JQuery autocompleter used for zones ("auto_zone") will look like:
<<
        <s:url id="url_zones" action="selectZone" />
        <sj:autocompleter
            id="auto_zone"
            name="name_zone"
            href="%{url_zones}"
            label="World Zones"
            list="zones"
            listKey="key"
            listValue="value"
            delay="30"
            loadMinimumCount="2"
            onSelectTopics="/autoZoneChange"
            />
>>
NOTE: <s:url id="url_zones" action="selectZone" /> defines the Struts Action data source for the autocompleter which will be discussed at "6. Struts 2 Actions".

4. Linking autocompleters
Supposing you have other autocompleters for countries, cities, you may want to obtain which cities are from a country and which countries are from a zone.
The JQuery autocompleter for countries ("auto_country") looks like:
<<
        <s:url id="url_countries" action="selectCountry" />
        <sj:autocompleter
            id="auto_country"
            name="name_country"
            href="%{url_countries}"
            label="World Countries"
            list="countries"
            listKey="key"
            listValue="value"
            delay="30"
            loadMinimumCount="2"
            onSelectTopics="/autoCountryChange"
            listenTopics="/autoZoneChanged"
            />
>>

If you want to link "auto_country" to "auto_zone", then you will have to use the "/autoZoneChange" event of "auto_zone" autocompleter; this will happen in JavaScript like this:
<<
    $.subscribe("/autoZoneChange",function(event, data){
        var ui = event.originalEvent.ui;
        if (ui.item && ui.item.text.length > 0) {
            //setting the URL of the child linked autocompleter
            setJQueryAutocompleterURL("/blogac/selectCountry.action", "cod_zone=" + ui.item.text, "countries", "auto_country", "name_country", "/autoCountryChange", "/autoZoneChanged");
        }
    },null);
>>

Note the presence of a JavaScript function, namely "setJQueryAutocompleterURL":
<<
function setJQueryAutocompleterURL(href, hrefparameter, list, id, name, selectTopics, listenTopics) {
    var opt_auto = {};
    opt_auto.delay = 30;
    opt_auto.minimum = 2;
    opt_auto.selectBox = false;
    opt_auto.selectBoxIcon = false;
    opt_auto.list = list;
    opt_auto.listkey = "key";
    opt_auto.listvalue = "value";
    opt_auto.jqueryaction = "autocompleter";
    opt_auto.id = id;
    opt_auto.name = name;
    opt_auto.onselecttopics = selectTopics;
    opt_auto.href = href;
    opt_auto.hrefparameter = hrefparameter;
    opt_auto.listentopics = listenTopics;
 
    jQuery.struts2_jquery.bind(jQuery('#' + id),opt_auto);
}
>>
This function practically passes the HTTP parameter "cod_zone" from "auto_zone" to "auto_country" when the "auto_zone" completed to render and user changed a value in it; when the user selects a zone, the "/autoCountryChange" event fires, and the function "setJQueryAutocompleterURL" populates the "auto_country" autocompleter with countries belonging to that zone.
Note that the "auto_country" autocompleter is waiting for another event to be published, namely "/autoZoneChanged", so, it will not be populated until after this event fires.

The same happens also for cities, the difference being the correspondence is now between countries and cities.

5. KeyValuePairBean:
This bean is used as a structure to store key/value pair for autocompleters.

6. Struts 2 Actions:
A JQuery autocompleter is rendered by various type of sources: Java list, JSON, JavaScript array, aso.
If you want to use JQuery Ajax capabilities, then you should render a JQuery autocompleter by using JSON type source.
When using Struts, the results are rendered by using Struts Actions, which represent the level of Controller from MVC architecture.
So, the Struts action should return a JSON type result.
To be sure of this, you have to include this annotation to your struts action:
<<
@ParentPackage("blog-json")
>>
This will use the Struts "blog-json" package defined in struts.xml, ie. it will extend the "json-default" package of the Struts2; "json-default" uses "struts2-json-plugin-2.2.1.jar" to render a JSON result.

To populate for example the zones, you will use this code:
<<
    @Override
    @Action(value="/selectZone", results={
        @Result(name="success", type="json"),
        @Result(name="input", location="/jsp/empty.jsp")
    })
    public String execute() {
        if (term != null && term.trim().length() > 1) {
            try {
                List<Zone> listZones = (List<Zone>)zoneDAO.findByCriteria("name", "%" + term.trim() + "%");
                zones = new ArrayList<KeyValuePairBean>();
                for (Zone zone : listZones) {
                    zones.add(new KeyValuePairBean(zone.getCod(), zone.getName()));
                }
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
                return ActionSupport.INPUT;
            }
        }
        return ActionSupport.SUCCESS;
    }
>>

Here:
"term" is sent by JQuery autocompleter and represents what was written in the "auto_zone" autocompleter to find zones;
"zones" is the Java List which will be rendered as a JSON object;
"zoneDAO" is the DAO (see "6. DAOs") managed by Spring over the Hibernate entities which contains methods as "findByCriteria()" in order to obtain data from database;

Also, you may observe here annotations to define the "success" and "input" results (overcomes) of the action "selectZone".

In the same action you should define getters and setters for "String term" and "List<KeyValuePairBean> zones".

Same you should do for countries and cities.
NOTE: to see how the Struts 2 Actions are accessed, and how their results are rendered, checkout also the "struts.xml" and "tiles.xml" files.

7. DAOs
DAOs, namely Data Access Objects, are used by Spring to obtain data from database via Hibernate.
DAOS are part of the business layer of a database web app.
A DAO class extends in this case the "HibernateDaoSupport" and contains methods to access the database via annotated Hibernate entities.
Any DAO should be described as a bean in the "applicationContext.xml" file in order to be seen by the sessionFactory; for example, for zones:
<<
    <bean id="ZoneDAO" class="blog.hibernate.dao.ZoneDAO">
        <property name="sessionFactory">
            <ref bean="sessionFactory" />
        </property>
    </bean>
>>

From Java point of view, a DAO should use a session manager, in this case, "HibernateDaoSupport" which is a Spring class that manages Hibernate sessions over annotated entities.
NOTE: a method that uses Hibernate session to get data from database uses HQL (Hibernate Query Language); to understand the HQL syntax you should google for HQL documentation.

8. Annotated Hibernate entities
An annotated entity is a POJO class that describes a database table by means of annotations.
It represents the Model from the MVC architecture.
For example, for the database table "zone", it was defined the Zone.java entity class; to refer table "zone" from database "blog", annotations are placed at the top of the class definition:
<<
@Entity
@Table(name = "zone", catalog = "blog")
>>
, while for each of table "zone" fields, there are specified on their value getters: primary key, foreign key, column name, field length, aso, if they exist.
Here are some examples of annotations, taken from Zone.java:
<<
    @Id
    @GeneratedValue
    @Column(name = "cod", unique = true, nullable = false, length = 4)
>>
<<
    @Column(name = "name", nullable = false, length = 45)
>>
<<
    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "zone")
>>

NOTE: if MyEclipse is used as IDE, you may generate both DAO and entity for each table by using Hibernate Reverse Engineering perspective.