第一种 实现 Servlet 接口，需要覆写 Servlet 的5个方法，并将ServletConfig对象保存到类级变量中
package app01a; import java.io.IOException;
import java.io.PrintWriter; import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebServlet; @WebServlet(name = "MyServlet", urlPatterns = {"/my"})
public class MyServlet implements Servlet {
private transient ServletConfig servletConfig; @Override
public void destroy() { } @Override
public ServletConfig getServletConfig() {
return servletConfig;
} @Override
public String getServletInfo() {
return "My Servlet";
} @Override
public void init(ServletConfig servletConfig) throws ServletException {
this.servletConfig = servletConfig; } @Override
public void service(ServletRequest resuest, ServletResponse response) throws ServletException, IOException {
String servletName = servletConfig.getServletName();
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.print("<html><head></head>"
+ "<body>Hello form "
+ servletName
+ "</body></html>");
}
}
第二种 继承抽象类 GenericServlet覆写service()方法
package app01a; import java.io.IOException;
import java.io.PrintWriter; import javax.servlet.GenericServlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet; @WebServlet(name = "GenericServletDemoServlet", urlPatterns = { "/generic" },
initParams = { @WebInitParam(name = "admin", value = "Harry taciak"),
@WebInitParam(name = "email", value = "admin@example.com")
}
)
public class GenericServletDemoServlet extends GenericServlet {
private static final long serialVersionUID = 1L; @Override
public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException {
ServletConfig servletConfig = getServletConfig();
String admin = servletConfig.getInitParameter("admin");
String email = servletConfig.getInitParameter("email");
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.print("<html><head></head><body>" +
"Admin: " + admin +
"<br/>Email: " + email +
"</body></html>");
} }
第三种 继承类 HttpServlet 覆写doGet()和doPost()方法 public abstract class HttpServlet extends GenericServlet
package app01c; import java.io.IOException;
import java.io.PrintWriter; import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse; @WebServlet(name = "SimleServlet", urlPatterns = {"/simple"})
public class SimpleServlet extends HttpServlet {
private static final long serialVersionUID = 1L; public SimpleServlet() {
super();
} /**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.println("<html>");
writer.println("<head>");
writer.println("</head>");
writer.println("<body>");
writer.println("This is the Simple Servlet");
writer.println("</body>");
writer.println("</html>");
} /**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
GenericServlet、HttpServlet是Servlet接口有两个默认的实现类。
HttpServlet在原有的Servlet接口上添加了一些HTTP协议的处理方法，是能够处理HTTP请求的Servlet。其功能比Servlet更加强大，因此开发人员在编写Servlet时，通常应继承HttpServlet类，而不是直接实现Servlet接口。
HttpServlet在实现Servlet接口时覆写了service()方法，该方法体内的代码会自动判断用户的请求，如果是Get请求，则自动调用HttpServlet的doGet()方法；如果是Post请求，则自动调用doPost()方法。通常开发人员在编写Servlet时，只需要覆写doGet()或doPost()方法，而不用再去覆写service()方法。