qr code scanner java app Improving the application with Seam in Java

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17.2 Improving the application with Seam
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The web application you ve written to search and edit web items can be improved if you add Seam into the mix. You start with basic Seam features:
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Seam makes the JSF backing bean unnecessary. You can bind JSF widget values and actions directly to EJB stateful and stateless session beans. Seam introduces a unified component model: All your classes can be turned into Seam components with annotations. Components are wired together in a loosely coupled fashion, with string expressions. Seam introduces new contexts and manages component scope automatically. This rich context model includes logical contexts that are meaningful to the application, such as a conversation or business-process context. Seam introduces a stateful programming model, which is great for conversations. A stateful application with Seam-managed conversations works in multiple browser windows with no extra effort.
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This is a short list of what Seam can do; there is much more that you ll put to use later. Let s first create a basic conversational, stateful, simple Seam application. Your first step is Seam setup and configuration. If you want to follow the examples with code, download the CaveatEmptor package for Seam from http://caveatemptor.hibernate.org, and open it in your IDE. This is also a good starting point if you want to code your own Seam project later.
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Introducing JBoss Seam
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17.2.1 Configuring Seam
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Figure 17.3 shows the files before and after the changes you make to the web application in the following sections.
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The application archive before and after Seam was introduced
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Two major changes are made: The JSF backing bean is no longer necessary, and the beans.jar archive has a new file, seam.properties. This file contains two Seam configuration options for this simple application (listing 17.7).
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Listing 17.7 A simple seam.properties configuration file
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org.jboss.seam.core.init.jndiPattern = caveatEmptor/#{ejbName}/local org.jboss.seam.core.manager.conversationTimeout = 600000
The first setting is necessary for Seam to integrate with an EJB 3.0 container. Because Seam is now responsible for wiring component instances at runtime, it
Improving the application with Seam
needs to know how to obtain EJBs through lookup. The JNDI pattern shown here is for JBoss application server. (Seam runs on any Java EE 5.0 server and even with and without EJB 3.0 in regular Tomcat. We think it s most convenient if you start with JBoss application server, because you don t need to install any extra services.) To completely integrate Seam with EJB 3.0, Seam also needs to intercept all calls to your EJBs. This is easy to do, thanks to EJB 3.0 support for custom interceptors. You won t see any interceptors in the code of your classes, because they re usually defined with a global wildcard that matches all EJBs in META-INF/ejb-jar.xml (not shown here). If you download a Seam example, it will have this file. The second setting in seam.properties defines that Seam can destroy an inactive user conversation after 600,000 milliseconds (10 minutes). This setting frees up memory in the HTTP session when a user decides to go to lunch. The seam.properties file is not only a configuration file for Seam it s also a marker. When Seam starts up, it scans the classpath and all archives for Seam components (classes with the right annotation). However, scanning all JARs would be too expensive, so Seam only scans JAR files and directories recursively that have a seam.properties file in the root path. Even if you don t have any configuration settings, you need an empty seam.properties file in the archive with your Seam component classes. You can find more Seam configuration options, and the integration with JSF and the servlet container, in web.xml and faces-config.xml. We ll get back to facesconfig.xml later; web.xml isn t interesting (see the commented file in the CaveatEmptor package). Seam can also be configured with a components.xml file in the WARs WEB-INF directory. You ll use that later when more complex configuration of components is required. (Much of Seam is written as Seam components. The string org.jboss.seam.core.manager is a component name, and conversationTimeout is a property you can access like any other component property.) Your next step is replacing the JSF backing bean with a Seam component.
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