Servlet 简介

protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException;

package indi.h13.servlet;  
  
import jakarta.servlet.ServletException;  
import jakarta.servlet.http.HttpServlet;  
import jakarta.servlet.http.HttpServletRequest;  
import jakarta.servlet.http.HttpServletResponse;  
  
import java.io.IOException;  
  
public class UserServlet extends HttpServlet {  
    @Override  
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {  
        String username = req.getParameter("username");  
        if("root".equals(username)) {  
            resp.getWriter().println("username is root");  
        } else {  
            resp.getWriter().println("username is not root");  
        }  
    }  
}

responce.setHeader("key", "value");

responce.setHeader("Content-Type", "image/jpeg");

@WebServlet("/ServletLifeCycleTest")  
public class ServletLifeCycle extends HttpServlet {  
    /**  
     * @brief 重写实例化方法  
     */  
    public ServletLifeCycle() {  
        System.out.println("ServletLifeCycle obj created.");  
    }  
  
    /**  
     * @brief 重写初始化方法  
     * @throws ServletException  
     * @note 注意需要重写的是无参数的 `init` 方法  
     */  
    @Override  
    public void init() throws ServletException {  
        super.init();  
        System.out.println("ServletLifeCycle obj inited.");  
    }  
  
    /**  
     * @brief 重写service方法  
     * @param req  
     * @param resp  
     * @throws ServletException  
     * @throws IOException  
     */    @Override  
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {  
        System.out.println("ServletLifeCycle.service() has been executed.");  
    }  
  
    /**  
     * @brief 重写销毁方法  
     */  
    @Override  
    public void destroy() {  
        super.destroy();  
        System.out.println("ServletLifeCycle obj has been destroyed.");  
    }  
}

public abstract class GenericServlet implements Servlet, ServletConfig, Serializable {  
    private static final long serialVersionUID = 1L;  
    private transient ServletConfig config;  
  
    public GenericServlet() {  
    }  
  
    public void destroy() {  
    }  
  
    public String getInitParameter(String name) {  
        return this.getServletConfig().getInitParameter(name);  
    }  
  
    public Enumeration<String> getInitParameterNames() {  
        return this.getServletConfig().getInitParameterNames();  
    }  
  
    public ServletConfig getServletConfig() {  
        return this.config;  
    }  
  
    public ServletContext getServletContext() {  
        return this.getServletConfig().getServletContext();  
    }  
  
    public String getServletInfo() {  
        return "";  
    }  
  
    public void init(ServletConfig config) throws ServletException {  
        this.config = config;  
        this.init();  
    }  
  
    public void init() throws ServletException {  
    }  
  
    public void log(String message) {  
        ServletContext var10000 = this.getServletContext();  
        String var10001 = this.getServletName();  
        var10000.log(var10001 + ": " + message);  
    }  
  
    public void log(String message, Throwable t) {  
        this.getServletContext().log(this.getServletName() + ": " + message, t);  
    }  
  
    public abstract void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;  
  
    public String getServletName() {  
        return this.config.getServletName();  
    }  
}

public void init(ServletConfig config) throws ServletException {  
    this.config = config;  
    this.init();  
}  

public void init() throws ServletException {  
}  

protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {  
    String method = req.getMethod();  
    long lastModified;  
    if (method.equals("GET")) {  
        lastModified = this.getLastModified(req);  
        if (lastModified == -1L) {  
            this.doGet(req, resp);  
        } else {  
            long ifModifiedSince;  
            try {  
                ifModifiedSince = req.getDateHeader("If-Modified-Since");  
            } catch (IllegalArgumentException var9) {  
                ifModifiedSince = -1L;  
            }  
  
            if (ifModifiedSince < lastModified / 1000L * 1000L) {  
                this.maybeSetLastModified(resp, lastModified);  
                this.doGet(req, resp);  
            } else {  
                resp.setStatus(304);  
            }  
        }  
    } else if (method.equals("HEAD")) {  
        lastModified = this.getLastModified(req);  
        this.maybeSetLastModified(resp, lastModified);  
        this.doHead(req, resp);  
    } else if (method.equals("POST")) {  
        this.doPost(req, resp);  
    } else if (method.equals("PUT")) {  
        this.doPut(req, resp);  
    } else if (method.equals("DELETE")) {  
        this.doDelete(req, resp);  
    } else if (method.equals("OPTIONS")) {  
        this.doOptions(req, resp);  
    } else if (method.equals("TRACE")) {  
        this.doTrace(req, resp);  
    } else {  
        String errMsg = lStrings.getString("http.method_not_implemented");  
        Object[] errArgs = new Object[]{method};  
        errMsg = MessageFormat.format(errMsg, errArgs);  
        resp.sendError(501, errMsg);  
    }  
  
}

public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {  
    HttpServletRequest request;  
    HttpServletResponse response;  
    try {  
        request = (HttpServletRequest)req;  
        response = (HttpServletResponse)res;  
    } catch (ClassCastException var6) {  
        throw new ServletException(lStrings.getString("http.non_http"));  
    }  
  
    this.service(request, response);  
}