Practical Apache Struts2 Web 2.0 Projects retail phần 8 pptx

<s:iterator status="rowstatus" value="parameters.event.options"> <s:property value="name"/> <s:if test="#rowstatus.last==false" >,</s:if> </s:iterator> </li> </ul> </p> Figure 8-8. The advanced search results, using a new eventListing.jsp template theme Consolidating List Actions The final consideration for the search use cases is whether the code can be optimized or consolidated. From the very beginning, the listEventResults.jsp template was developed with reusability in mind. Because there were several search uses cases, and each needed to dis- play results, a common results page was developed. To provide the generic canvas that any CHAPTER 8 ■ SEARCHING AND LISTINGS232 9039ch08.qxd 10/29/07 3:27 PM Page 232 action could use, the template used properties from the calling action to provide context i nformation to the user. The downside of this approach is that each and every calling action is now required to provide these properties. When the search actions were being developed, the commonality required to render the result was missed, and it’s now time to return and extract the common elements. The first step is to create a base class and extract the common elements. Each of these elements has been covered in detail previously: • The property and setter that allows the EventService business service to be used by the action • The property and getter for the list of resulting events • The property and getter for the description of the search that was just performed • A getter that allows the JSP to select the correct template to render the event details The base class BaseSearchAction (listing is shown next) is the result of extracting the common elements. To ensure that developers subclass the action class correctly, and all the elements necessary to render the results are provided, the class is made abstract along with the getEventTemplate() method. public abstract class BaseSearchAction extends BaseAction { protected String userInfo; protected List<Event> results; protected EventService service; public void setEventService(EventService service) { this.service = service; } public List<Event> getResults() { return results; } public String getUserInfo() { return userInfo; } public abstract String getEventTemplate(); } After a search base class is created, each of the search use case action implementations can be refactored to extend it. The resulting action classes are much smaller, and more impor- tantly, focused on a single responsibility: providing the functionality of the use case with the clutter of the search result infrastructure removed. CHAPTER 8 ■ SEARCHING AND LISTINGS 233 9039ch08.qxd 10/29/07 3:27 PM Page 233 The SearchByTitleAction action becomes @ ParentPackage("base-package") @Result(name="success",value= "/WEB-INF/jsp/search/listEventResults.jsp") public class SearchByTitleAction extends BaseSearchAction { private String titlePartial; public void setTitlePartial(String titlePartial) { this.titlePartial = titlePartial; } public String getEventTemplate() { return "apress"; } public String execute() throws Exception { results = service.findByTitle(titlePartial); userInfo = "".equals(titlePartial) ? getText("searchBy.all") : getText("searchBy.title", new String[]{titlePartial}); return SUCCESS; } } The SearchForEventsAction action class (listing is shown next) is longer than the SearchByTitleAction action class; however, it provides the same focus on a single responsibility. @ParentPackage("base-package") @Result(name="success",value= "/WEB-INF/jsp/search/listEventResults.jsp") public class SearchForEventsAction extends BaseSearchAction { private String locationName; private String locationCity; private String locationState; private String contestants; // setters for the form field properties public String getEventTemplate() { return "apress/extended"; } CHAPTER 8 ■ SEARCHING AND LISTINGS234 9039ch08.qxd 10/29/07 3:27 PM Page 234 public String execute() throws Exception { results = service.findEventsByExample( createQueryLocation(), createContestantsList () ); userInfo = getText("searchBy.advanced"); return SUCCESS; } private Location createQueryLocation() { // create a Location instance for the individual fields } private List<String> createContestantsList() { // create a list of strings } } There is yet another option for combining the search actions. Instead of developing a base class and individual subclasses, you can place all the logic for all of the search use cases in a single action class. This approach is useful when the parameters being passed to the different search use cases are similar; that is, there is approximately the same number of terms, and they are of the same type. Under this circumstance, the only difference is the action logic method (the renamed execute() method). When the use cases are like the search use cases developed in this chapter, separate action classes should be used. If all the use cases are lumped together, the action class is too overrun with properties that are conditional on the use case being invoked. This leads to con- fusion about when properties are being used and when they aren’t and is a bad example if used in other areas of the web application. As an example of how it can be achieved, the code for an all-encompassing SearchAction is provided here: public class SearchAction extends BaseAction { private String userInfo; private String eventTemplate; private List<Event> results; private EventService service; // all the search use cases' properties (quick search and advanced search) public void setEventService(EventService service) { this.service = service; } CHAPTER 8 ■ SEARCHING AND LISTINGS 235 9039ch08.qxd 10/29/07 3:27 PM Page 235 public List<Event> getResults() { return results; } public String getUserInfo() { return userInfo; } public String getEventTemplate() { return eventTemplate; } public String searchByTitle() { // the quick search logic } public String searchByLocationAndContestants() { // the advanced search logic } } Summary By now, you should have a good understanding of how to implement search functionality and how to display the results. Along with the search functionality, you saw techniques for creating focused actions, dividing up the view rendering into multiple JSPs, and creating generic JSP templates. You should also be comfortable modifying SiteMesh templates to provide addi- tional user interface elements, as well as adding new links to the navigation panel. During the development of the web application, the underlying business service imple- mentation of the search functionality was intentionally not discussed because it’s not relevant to accessing and rendering the results using Struts2. If you look into the provided code, you’ll see that the underlying implementation is a simple Hiber nate query . This is one of the many different ways to perform searching and, as indicated in the sidebar on pagination, there are many technology considerations, as well as nonfunctional considerations, that need to be taken into account when selecting an implementation. From a purely technological standpoint, Hibernate or direct JDBC using SQL or stored procedures can be used, or a library such as Lucene can be integrated. Each of these methods has pr os and cons. The important thing to remember, and the reason why this was not dis- cussed earlier, is that the implementation details do not (and should not) have an impact on how the results are obtained and how they are rendered. Everything discussed in this chapter is applicable to any of these implementations. CHAPTER 8 ■ SEARCHING AND LISTINGS236 9039ch08.qxd 10/29/07 3:27 PM Page 236 Syndication and Integration In the new era of Web 2.0 development, developing an island of functionality that users access from a web browser is no longer enough. Web sites are a main focus and a starting point but no longer the only means of accessing the information. Mashups are one example of an alternative way to access and use data from a web site; a mashup takes information from many different sources and combines it in ways that were not considered by the origi- nal developer. Google Maps is a great example of this technology. It is remarkably easy to take an API or RSS feed and combine it with a Google Map to provide a geographical representa- tion of what was originally purely textual information. Further still, web sites have sprung up that are themselves mashups. The bulk of their functionality is simply aggregated content from other sites, with an overlay of social networking functionality to bring it all together. In this chapter, you will learn about the different options to provide syndication and inte- gration in web applications. First we’ll discuss a RSS (Really Simple Syndication) feed, then consuming the RSS feed to create a mashup, and finally providing a REST (Representational State Transfer) style web service to access data. ■Caution Before the code in this chapter can be run, several artifacts need to be installed into the local Maven2 repository. The instructions on how to install the required artifacts can be found in the section “Configuration for the GeoRSS Module.” The Use Case This chapter has only one use case: Publish Event Information. The event information that has been entered by users should be available externally, as well as through the web application. B y exposing event details to a wider audience and bey ond the boundaries of our original site, more people will be exposed to our service. In turn, this has the possibility to bring more peo- ple to our web application. T o implement this use case , y ou will first implement an RSS feed. Additionally, a RESTful web service will be developed to provide another integration option for the web application. 237 CHAPTER 9 9039ch09.qxd 10/29/07 3:26 PM Page 237 Implementing RSS T he first style of syndication being implemented is RSS (Really Simple Syndication), more specifically RSS version 2.0. RSS was first available in 1999 in the “My Netscape” portal and was the first syndication t echnology to gain widespread acceptance and use. Since then, the acronym RSS has several different interpretations depending on the version: • RSS 2.0: Really Simple Syndication. • RSS 1.0 & 0.90: RDF (Resource Description Framework) Site Summary. • RSS 0.91: Rich Site Summary. At its core, RSS is XML, where each different version of RSS has a slightly different DTD or XML Schema. Here is an example of RSS 2.0 source that comes from a feed on the Apache Software Foundation’s site: <?xml version="1.0" encoding="UTF-8"?> <rss version="2.0"> <channel> <title>Apache Software Foundation Struts2 RSS Feed</title> <link>http://cwiki.apache.org/confluence</link> <description> The 5 most recent creations of or modifications to pages, blogposts, mails, comments, attachments less than 200.0 days old in space Apache Struts 2 Wiki. </description> <item> <title>Articles and press (updated)</title> <link> http://cwiki.apache.org/confluence/display/S2WIKI/Articles+and+press </link> <description>&lt;div id="PageContent"&gt; …</description> <pubDate>Thu, 14 Jun 2007 15:04:43 GMT</pubDate> <guid> http://cwiki.apache.org/confluence/display/S2WIKI/ Projects+Using+WebWork+or+Struts2</guid> </item> <item> <title>Companies that provide Struts 2 support (updated)</title> <link> http://cwiki.apache.org/confluence/display/S2WIKI/Companies+that +provide+Struts+2+support CHAPTER 9 ■ SYNDICATION AND INTEGRATION238 9039ch09.qxd 10/29/07 3:26 PM Page 238 </link> <description>&lt;div id="PageContent"&gt; …</description> <pubDate>Sun, 27 May 2007 01:27:04 GMT</pubDate> <guid> http://cwiki.apache.org/confluence/display/S2WIKI/ Companies+that+provide+Struts+2+support</guid> </item> … </channel> </rss> Basically an RSS feed has a channel. A channel has basic information that includes title, link, and description, as well as a list of item elements. The item elements provide the detailed information, which includes the same elements as the channel (title, link, and description) and additional fields for pubDate and guid. These are not the only elements available, but they are the required elements. More information can be obtained from the RSS specification. ■Note The RSS 2.0 specification can be obtained at http://www.rssboard.org/rss-specification; here you will find an extensive list of the optional elements not included in this example. In Chapter 8, functionality was developed to retrieve a list of events and render the results in HTML. The same functionality can be reused here; however, to render RSS rather than HTML, the result format needs to be changed. The chosen option for rendering RSS is a new result type. Using a new result type allows any action that contains a list of Event objects to be turned into a RSS feed quickly and easily. To generate the correct XML for the RSS feed, the Rome library will be used. Rome is an open source library that supports all of the RSS version formats, as well as Atom. ■Note Atom is a concurring standard with RSS and provides a complete publishing protocol tha t is HTTP- based. It is also an IETF (Internet Engineering Task Force) standard, RFC 4287 ( http://www.ietf.org/ rfc/rfc4287.txt ). A good reference for the differences between the RSS and Atom protocols can be found in the Wikipedia at http://en.wikipedia.org/wiki/Atom_%28standard%29. As w ell as cr eating feeds , Rome provides functionality to read feeds, aggregate feeds, and convert between different feed formats. Most importantly, Rome allows you to interact with the feed using Java objects rather than the raw XML. Figure 9-1 shows an example of the com- pleted RSS r esult type displaying ev ent infor mation in a browser. CHAPTER 9 ■ SYNDICATION AND INTEGRATION 239 9039ch09.qxd 10/29/07 3:26 PM Page 239 ■Tip More information on the Rome library can be obtained from https://rome.dev.java.net. Figure 9-1. The result of an RSS feed in a browser The R ome JAR files are included in the application by adding the following dependency to the Maven pom.xml configuration file: <dependency> <groupId>rome</groupId> <artifactId>rome</artifactId> <version>0.9</version> </dependency> CHAPTER 9 ■ SYNDICATION AND INTEGRATION240 9039ch09.qxd 10/29/07 3:26 PM Page 240 Results and Result Types In previous chapters, you have learned how to use existing Struts2 result types. Now you’ll learn how to implement a new result type. The basic implementation is easy; simply imple- m ent the R esult i nterface. public interface Result extends Serializable { public void execute(ActionInvocation invocation) throws Exception; } When the result is configured for an action, the execute() method is invoked to generate the final outcome that is returned to the user. As you can see, result types are very similar to actions in that a result is executed (by a provided execute() method). In the dispatcher, velocity, and freemarker results, the out- come is returning HTML to the user, but there are other options. The redirect and redirectAction results forward the user to a different URL or action, the stream result streams data directly to the browser using a specific MIME type, and the httpheader result can modify the HTTP headers in the response. Result types are also similar to interceptors in that all the information that is needed to execute must be obtained from the ActionInvocation object. This makes results slightly differ- ent from actions, which can gain access to additional objects from the executing environment via dependency injection. (Although objects cannot be injected, parameters that are specified in the result configuration are injected into setter on the result type.) Configuring Result Types Most of the actions previously developed have been configured via annotations. The same approach could be taken for configuring the action using the new RSS result type: create a new action (a copy, because an action already exists with the same functionality) and config- ure it with the RSS result type annotation. However, this means that exactly the same code is required with the only difference being a different result annotation. Because the action class has already been developed, all that is needed is a different con- figuration. By providing a new action configuration in the struts.xml configuration file, a new URL can be used to inv oke the same action class , and a different result type can be used in rendering the result. There are two elements in configuring a new result type. The first is declaring the implementation class of the new result type, along with the unique name that will be used to specify the result type in the action’s configuration. This is done at the package level, before the actions are configured. The name attribute specifies the unique name to use in further configuration, and the class attribute specifies the class name of the new result type: CHAPTER 9 ■ SYNDICATION AND INTEGRATION 241 9039ch09.qxd 10/29/07 3:26 PM Page 241 [...]... Most Recent Events http://localhost :80 80/app/rss.action The most recent events in RSS format Boston Marathon 20 08 http://localhost :80 80/app/api/event/3 …... INTEGRATING SOAP WEB SERVICES Because the SOAP style of web services is RPC based, the integration point is a closer fit to the business services layer than the web layer For that reason, they will not be covered in this book The usual configuration with web applications is a secondary HTTP access point (usually provided via a servlet), which is configured in the web. xml configuration file Additional web service... Boston Marathon 20 08 http://localhost :80 80/app/api/event/3 … Thu, 03 Apr 20 08 13:00:00 GMT http://localhost :80 80/app/api/event/3 20 08- 04-03T13:00:00Z 42.3 586 4 -71.05665 … There is only one change to the XML, which consists of two new... 300px"> Implementing Web Services Along with syndication, web services are the primary means of integrating web applications Whereas syndication, especially RSS, provides an outgoing read-only information stream, web services allow other programs to interact by submitting data as well as requesting data There are two types of web services: SOAP (Simple Object Access Protocol)... easily think of RESTful web services as objects that actions are performed on For SOAP web services, think of actions that are performed with parameters (that may or may not be objects) s Note The Wikipedia is a great source for more information on both styles of web services For more information on SOAP web services, the URL is http://en.wikipedia.org/wiki/SOAP, and for RESTful web services, the URL... Access Protocol) and REST (Representational State Transfer) SOAP Web Service: This style of web service is a form of RPC (Remote Procedure Call), where both the request and response of the call is XML Although the calls are primarily , transmitted over HTTP, the transport can be JMS, SMTP or even FTP SOAP-style web services use WSDL (Web Service Description Language) to define the API, may use UDDI... WS-Addressing, WS-Transaction, etc.) for application-level cross-cutting concerns All of this provides a complete and robust infrastructure for web services; however, for the majority of web applications, it is far too complex RESTful Web Service: On the other hand, RESTful web services are lightweight, primarily use HTTP and focus around the concept of using URIs (Uniform Resource Identifiers) to , identify... SYNDICATION AND INTEGRATION map.setCenter(new GLatLng(41 .87 5696, -87 .624207), 3); map.addControl(new GLargeMapControl()); Next, the RSS feed needs to be downloaded so the location information can be accessed Google provides a GDownloadUrl object that accepts a URL for input, and upon loading, calls a user provided function GDownloadUrl( "http://localhost :80 80/app/rss.action", function(data, responseCode) { . http://localhost: 80 8 0/app/rss.action and http://localhost: 80 8 0/app/atom.action, respectively. CHAPTER 9 ■ SYNDICATION AND INTEGRATION2 48 903 9ch09.qxd 10 /29 /07 3 :26 PM Page 24 8 <struts> <package. 20 08& lt;/title> <link>http://localhost: 80 8 0/app/api/event/3</link> <description>…</description> <pubDate>Thu, 03 Apr 20 08 13 :00 :00 GMT</pubDate> <guid>http://localhost: 80 8 0/app/api/event/3</guid> <dc:date> ; 20 08 -04 -03 T13 :00 :00 Z</dc:date> <geo:lat> 42. 3 586 4</geo:lat> <geo:long>-71 .05 665</geo:long> </item> … </channel> </rss> There. any of these implementations. CHAPTER 8 ■ SEARCHING AND LISTINGS236 903 9ch 08. qxd 10 /29 /07 3 :27 PM Page 23 6 Syndication and Integration In the new era of Web 2. 0 development, developing an island