Servlet 和 Web-App
只有 EJB 還是不足夠的, 我們要寫一個 Servlet 去使用 EJB 計算斐波納契數列.
在項目中新增一個 class, package 輸入 ‘tutorial.web’ 和名稱輸入為 ‘ComputeServlet’. 按下 ‘Browse…’ 在 superclass 新增 ‘HTTPServlet’. 選 ‘Constructors from superclass’ 和 ‘Inherited abstract methods’.
按 ‘Finish’ 後應可看到以下畫面. 
開啟 ‘ComputeServlet.java’ 檔案. 右擊右手方視窗選 ‘Source’ -> ‘Override/Implement Methods…’. 選 ‘init’ 和 ‘doPost’ 方法再按 ‘OK’, 這兩個方法會自動生成.
接著加上兩個 private 成員:
private FiboHome home;
private String value;
定義 ‘init’ 方法如下, 這是將 EJB Home 接口初始化:
public void init() throws ServletException {
try {
Context context = new InitialContext();
value = (String) context.lookup("java:/comp/env/Title");
Object ref = context.lookup("java:/comp/env/ejb/Fibo");
home = (FiboHome) PortableRemoteObject.narrow(ref, FiboHome.class);
} catch (Exception e) {
throw new ServletException("Lookup of java:/comp/env/ failed");
}
}
定義 ‘doPost’ 方法如下, 這是得到一個 ‘limit’ 要求後, 新增一個 EJB 實例計算後將結果輸出致 HTML:
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html><head><title>");
out.println(value);
out.println("</title></head>");
out.println("<body>");
out.println("<h1>");
out.println(value);
out.println("</h1>");
try {
Fibo bean = home.create();
int limit = 0;
String value = request.getParameter("limit");
if (value != null) {
try {
limit = Integer.parseInt(value);
} catch (Exception e) {}
}
double[] result = bean.compute(limit);
bean.remove();
out.println("<p>");
out.print("The ");
out.print(limit);
out.print(" first Fibonacci numbers ");
for (int i = 0; i < result.length; i++) {
out.println("<br>");
out.println(i);
out.println(" : ");
out.println(result[i]);
}
out.println("</p>");
}
catch (Exception e) {
out.println(e.getMessage());
e.printStackTrace(out);
}
finally {
out.println("</body></html>");
out.close();
}
}
下一步是插入 Servlet XDoclet javadoc 相關的標籤. 在 javadoc 裏寫入 ‘@web’ 和按下 CTRL+Space. 應看到自動完成功能. 而其他的屬性亦一樣做法, 代碼如下:
*
* @web.servlet name = "ComputeServlet"
* display-name = "Computation Servlet"
* description = "Servlet that compute Fibonacci suite"
*
* @web.servlet-mapping url-pattern = "/Compute"
*
* @web.env-entry name = "Title"
* type = "java.lang.String"
* value = "Fibonacci computation"
* description = "Example of Env Entry"
*
* @web.ejb-ref name = "ejb/Fibo"
* type = "Session"
* home = "tutorial.interfaces.FiboHome"
* remote = "tutorial.interfaces.Fibo"
* description = "Reference to the Fibo EJB"
*
* @jboss.ejb-ref-jndi ref-name = "ejb/Fibo"
* jndi-name = "ejb/tutorial/Fibo"
*/
public class ComputeServlet extends HttpServlet {
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