前文中记录了Servlet接口的相关内容，本文主要记录GenericServlet、HTTPServlet和其关系。
GenericServlet
讲解从如下实例开始，发现使用GenericServlet时并没有像Servlet接口一样需要实现之前那五种方法，只有一个Service()方法，原因我们从源码中寻找。
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="[email protected]")
}
)
public class GenericServletDemoServlet extends GenericServlet {
private static final long serialVersionUID = 62500890L;
@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>");
}
}
源码如下：
public abstract class GenericServlet implements Servlet, ServletConfig,
java.io.Serializable {
private static final long serialVersionUID = 1L;
private transient ServletConfig config;
public GenericServlet() {
// NOOP
}
@Override
public void destroy() {
// NOOP by default
}
@Override
public String getInitParameter(String name) {
return getServletConfig().getInitParameter(name);
}
@Override
public Enumeration<String> getInitParameterNames() {
return getServletConfig().getInitParameterNames();
}
@Override
public ServletConfig getServletConfig() {
return config;
}
@Override
public ServletContext getServletContext() {
return getServletConfig().getServletContext();
}
@Override
public String getServletInfo() {
return "";
}
@Override
public void init(ServletConfig config) throws ServletException {
this.config = config;
this.init();
}
public void init() throws ServletException {
// NOOP by default
}
public void log(String message) {
getServletContext().log(getServletName() + ": " + message);
}
public void log(String message, Throwable t) {
getServletContext().log(getServletName() + ": " + message, t);
}
@Override
public abstract void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException;
@Override
public String getServletName() {
return config.getServletName();
}
}
可以看到GenericServlet接口中源码已经帮我们实现了这些方法，只有Service没有实现，这就很清楚了，GenericServlet其实就是继承了Servlet接口和ServletConfig，用法其实和Servlet接口一样。
HTTPServlet
由于HttpServlet的源码比较长，我这里就不再粘贴了，可以参考这个链接，详细明确https://blog.csdn.net/u010398771/article/details/82758022
总结：三者其实就是逐渐方便用户的一个体现，能封装的都封装掉，使用的时候方便省事。