11.7 Servlet技术在WAP开发中的应用
WAP开发中应用Servlet技术时要利用专用WAP服务器软件，如Nokia WAP Server等提供的开放程序接口来编写具体的程序。我们仍以WML为例，它应用Servlet编程的规则与应用JSP时的规则基本相同，我们不再逐条给出解释。通过下面的简单例子，结合JSP的编写规则，大家不难了解Servlet编写WML页面的基本规则：
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class WapServlet extends HttpServlet
{
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, java.io.IOException
{
response.setContentType("text/vnd.wap.wml");
PrintWriter out = response.getWriter();
xmlHeader(out);
out.println("<wml>");
out.println("<card title = "JavaTest">");
out.println("<p>Hello! This comes from a servlet!</p>");
out.println("</card>");
out.println("</wml>");
}
public void xmlHeader(PrintWriter out)
{
out.println("<?xml version="1.0"?>");
out.println("<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN" "+
""http://www.wapforum.org/DTD/wml_1.1.xml">");
}
}
下面我们给出一个简单的Servlet程序，它可在WAP浏览器上显示“The simple HelloWorld servlet.”的信息。程序清单如下：
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloWorld extends HttpServlet
{
String m_text;
public void init(ServletConfig config) throws ServletException
{
super.init(config);
m_text = config.getInitParameter("text");
if (m_text == null)
{
m_text = "This is a simple test servlet.";
}
}
public void doGet(HttpServletRequest request,HttpServletResponse response) throws IOException, ServletException
{
PrintWriter out = response.getWriter();
out.println("<?xml version="1.0"?>");
out.println("<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML1.1//EN""http://www. wapforum.org/DTD/wml_1.1.xml/">");
out.println("<wml>");
out.println("<card id="card1" title="Hello World">");
out.println("<p>");
out.println(m_text);
out.println("</p>");
out.println("</card>");
out.println("</wml>");
// Remember to close the out object
out.close();
}
public String getServletInfo( )
{
return "The simple HelloWorld servlet.";
}
}