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<document> <header> <product>resin-ee</product> <title>Property-based Persistent Object</title> <description> <p>Basic persistence example showing configuration, classes, and client code for a single-table bean.</p> <p>This example focuses on:</p> <ul> <li>Introduces persistence fundamental concepts</li> <li>Setting up the database</li> <li>Developing the Entity classes</li> <li>Developing a Servlet to lookup and use the entity bean</li> <li>Configuring Resin to deploy the bean and use JNDI</li> </ul> </description> <type>tutorial</type> <tutorial-startpage>basic</tutorial-startpage> </header> <body> <summary/><s1><p>Amber's persistence manages tables in a relational database using a Javabean interface. Each database table corresponds to a single "entity bean". By creating an entity bean with container managedpersistence, you let Amber generate the SQL to load, store, andcache entity beans from the database. Avoiding SQL is an advantage initself, but the primary advantage is the increased flexiblity of yourapplication code. Maintenance and code-refactoring can focus on thebeans instead of changing lots of SQL statements in the program.</p></s1><s1 title="Files in this tutorial"><deftable><tr><td><viewfile-link file="WEB-INF/resin-web.xml"/> </td><td>resin-web.xml configuration</td></tr><tr><td><viewfile-link file="WEB-INF/classes/META-INF/persistence.xml"/> </td><td>persistence.xml configuration</td></tr><tr><td><viewfile-link file="WEB-INF/classes/example/CourseBean.java"/> </td><td>The course bean</td></tr><tr><td><viewfile-link file="WEB-INF/classes/example/CourseServlet.java"/> </td><td>The course servlet</td></tr></deftable></s1><s1 title="Database Schema"><example title="course.sql">CREATE TABLE basic_courses ( id INTEGER PRIMARY KEY auto_increment, course VARCHAR(250), teacher VARCHAR(250));INSERT INTO basic_courses VALUES('Potions', 'Severus Snape');INSERT INTO basic_courses VALUES('Transfiguration', 'Minerva McGonagall');</example></s1><s1 title="Overview"><p>To find and enhance a persistent Java bean, Amber follows the followingprocedure.</p><ol><li><ejb-server> in the resin-web.xml configures Amber to start looking for persistence.xml in the classpath.</li><li>The persistence.xml in WEB-INF/classes/META-INF tells Amber to create a persistence-unit named "example".</li><li>The "example" persistence-unit contains a class example.CourseBean</li><li>Amber enhances example.CourseBean as a persistent object.</li></ol><p>By the end of initialization time, Amber has enhanced CourseBean andmade it available to the application in the persistence-unit "example".</p><p>A servlet will then lookup the CourseBean with the following procedure:</p><ol><li>Obtain an EntityManager for the persistence unit from JNDI either directly as java:comp/env/persistence/PersistenceContext/example, or using the @PersistenceUnit injection annotation.</li><li>Use the EntityManager to find the instance of the bean.</li></ol></s1><s1 title="Bean Implementation"><example title="CourseBean.java">package example;import javax.persistence.*;<a href="doc|amber-table.xtp#@Entity">@Entity</a><a href="doc|amber-table.xtp#@Table">@Table</a>(name="amber_basic_course")public class CourseBean { private int _id; private String _course; private String _teacher; <a href="doc|amber-table.xtp#@Id">@Id</a> <a href="doc|amber-table.xtp#@Column">@Column</a>(name="id") <a href="doc|amber-table.xtp#@GeneratedValue">@GeneratedValue</a> public int getId() { return _id; } public void setId(int id) { _id = id; } <a href="doc|amber-table.xtp#@Basic">@Basic</a> public String getCourse() { return _course; } public void setCourse(String course) { _course = course; } <a href="doc|amber-table.xtp#@Basic">@Basic</a> public String getTeacher() { return _teacher; } public void setTeacher(String teacher) { _teacher = teacher; }}</example><p>With Resin, all the Java source can be dropped in WEB-INF/classes.Resin will automatically compile any changes and regenerate the persistenceclasses, stubs and skeletons.</p></s1><s1 title="Resin Configuration"><p>Now that we've built the bean, we need toattach it to Resin. The entity bean is deployed usingthe <code>ejb-server</code> resource.</p><example title="WEB-INF/resin-web.xml"><web-app> <!-- server configuration --> <ejb-server data-source="jdbc/resin"/> <servlet servlet-name="basic" servlet-class="example.CourseServlet"/> <servlet-mapping url-pattern="/basic" servlet-name="basic"/></web-app></example></s1><s1 title="persistence.xml"><p>The persistence.xml lives in META-INF/persistence.xml. Sincewe're developing in WEB-INF/classes, the file will be inWEB-INF/classes/persistence.xml.</p><example title="WEB-INF/classes/META-INF/persistence.xml"><persistence xmlns="http://java.sun.com/xml/ns/persistence" version="1.0"> <persistence-unit name="example"> <class>example.CourseBean</class> <exclude-unlisted-classes/> </persistence-unit></persistence></example></s1><s1 title="Client Servlet"><example title="CourseServlet.java">import javax.persistence.*;public class CourseServlet extends HttpServlet { @PersistenceUnit(name="example") private EntityManager _manager; public void service(HttpServletRequest req, HttpServletResponse res) throws java.io.IOException, ServletException { PrintWriter out = res.getWriter(); res.setContentType("text/html"); CourseBean []course = new CourseBean[2]; course[0] = _manager.find(CourseBean.class, new Integer(1)); course[1] = _manager.find(CourseBean.class, new Integer(2)); out.println("<h3>Course Details</h3>"); for (int i = 0; i < course.length; i++) { out.println("course: " + course[i].getCourse() + "<br>"); out.println("teacher: " + course[i].getTeacher() + "<br>"); out.println("<br>"); } }}</example><results><h3>Course Details</h3>course: Potionsinstructor: Severus Snapecourse: Transfigurationinstructor: Minerva McGonagall</results></s1><s1 title="Conclusion"><p>The core of Amber's persistence management is its management of asingle table. Much of the work underlying the database management ishidden from the applicaton. Transaction management and caching happenautomatically. For example, once the course has been loaded from thedatabase, Amber does not need to query the database again untilthe course changes. So read-only requests, the most common, can avoidall database traffic.</p><p>More complicated applications build on the single tablemanagement. The following examples add more realistic features tothis example: using queries to <a href="../amber-query/index.xtp">find allcourses</a> and <a href="../amber-create/index.xtp">creating</a> new database rows.</p></s1> </body></document>⌨️ 快捷键说明
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