在web.xml中使用資源注射(@Resource) (Tomcat7此路不通，Tomcat6大多可以)

喜氣蜘蛛 2014-03-01

展開全文

資源注射是從JavaEE 5.0開始出現，實現了Tomcat在啟動時自動將web.xml中的配置信息“注射”到Servlet中。資源注射是通過Annotation完成，Annotation是一種特殊的接口，以"@"為標志，用法如下：

[java] view plain copy print ?

有時為了簡潔，上面的兩行代碼可以縮寫為一行：

[java] view plain copy print ?

加入@Resource注釋后，Tomcat會在Servlet運行時將變量message的值注入，這個值設置在web.xml中名為messageNameInWebXml的參數中。

下面用實例來說明：

[java] view plain copy print ?

package com.hello.servlet;
import java.io.*;
import javax.annotation.Resource;
import javax.servlet.*;
import javax.servlet.http.*;
public class InjectionServlet extends HttpServlet{
private @Resource(name="hello") String hello;
private @Resource(name="i") int i;
@Resource(name="persons")
private String persons;
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
response.setCharacterEncoding("UTF-8");
request.setCharacterEncoding("UTF-8");
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional //EN\">");
out.println("<HTML>");
out.println("<HEAD><TITLE>資源注入</TITLE></HEAD>");
out.println("<style>body{font-size:12px;}</style>");
out.println("注入的字符串: - " + hello +" ");
out.println("注入的整數: - " + i +" ");
out.println("注入的字符串數組: ");
for(String person : persons.split(",")){
out.println(" - " + person +" ");
}
out.println("<BODY>");
out.println("</BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
}

下一步，在web.xml中使用標簽<env-entry>來配置資源。<env-entry>僅能配置java.lang包下標準類型的變量，如String, Integer, Double等。配置后的代碼如下：

[html] view plain copy print ?

<servlet>
<servlet-name>InjectionServlet</servlet-name>
<servlet-class>com.hello.servlet.InjectionServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>InjectionServlet</servlet-name>
<url-pattern>/servlet/InjectionServlet</url-pattern>
</servlet-mapping>
<env-entry>
<env-entry-name>hello</env-entry-name>
<env-entry-type>java.lang.String</env-entry-type>
<env-entry-value>Hello, Welcome to the JavaEE Resource Injection</env-entry-value>
</env-entry>
<env-entry>
<env-entry-name>i</env-entry-name>
<env-entry-type>java.lang.Integer</env-entry-type>
<env-entry-value>14</env-entry-value>
</env-entry>
<env-entry>
<env-entry-name>persons</env-entry-name>
<env-entry-type>java.lang.String</env-entry-type>
<env-entry-value>Helloween, Cobain, Roses, WLJ, </env-entry-value>
</env-entry>