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6. Servlet的体系结构    

    Servlet -- 接口         |     GenericServlet -- 抽象类         |     HttpServlet  -- 抽象类

    * GenericServlet：将Servlet接口中其他的方法做了默认空实现，只将service()方法作为抽象

        * 将来定义Servlet类时，可以继承GenericServlet，实现service()方法即可

    * HttpServlet：对http协议的一种封装，简化操作

        1. 定义类继承HttpServlet         2. 复写doGet/doPost方法

package com.learn.web.servlet;import javax.servlet.*;import javax.servlet.annotation.WebServlet;import java.io.IOException;@WebServlet("/demo1")public class ServletDemo1 implements Servlet {    @Override    public void init(ServletConfig servletConfig) throws ServletException {    }    @Override    public ServletConfig getServletConfig() {        return null;    }    @Override    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {        System.out.println("demo1....");    }    @Override    public String getServletInfo() {        return null;    }    @Override    public void destroy() {    }}

package com.learn.web.servlet;import javax.servlet.GenericServlet;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.annotation.WebServlet;import java.io.IOException;@WebServlet("/demo2")public class ServletDemo2 extends GenericServlet {    @Override    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {        System.out.println("demo2.....");    }}

//// Source code recreated from a .class file by IntelliJ IDEA// (powered by Fernflower decompiler)//package javax.servlet;import java.io.IOException;import java.io.Serializable;import java.util.Enumeration;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
   
     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 msg) {        this.getServletContext().log(this.getServletName() + ": " + msg);    }    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();    }}
   

//// Source code recreated from a .class file by IntelliJ IDEA// (powered by Fernflower decompiler)//package javax.servlet.http;import java.io.IOException;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.text.MessageFormat;import java.util.Enumeration;import java.util.ResourceBundle;import javax.servlet.DispatcherType;import javax.servlet.GenericServlet;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public abstract class HttpServlet extends GenericServlet {    private static final long serialVersionUID = 1L;    private static final String METHOD_DELETE = "DELETE";    private static final String METHOD_HEAD = "HEAD";    private static final String METHOD_GET = "GET";    private static final String METHOD_OPTIONS = "OPTIONS";    private static final String METHOD_POST = "POST";    private static final String METHOD_PUT = "PUT";    private static final String METHOD_TRACE = "TRACE";    private static final String HEADER_IFMODSINCE = "If-Modified-Since";    private static final String HEADER_LASTMOD = "Last-Modified";    private static final String LSTRING_FILE = "javax.servlet.http.LocalStrings";    private static final ResourceBundle lStrings = ResourceBundle.getBundle("javax.servlet.http.LocalStrings");    public HttpServlet() {    }    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        String protocol = req.getProtocol();        String msg = lStrings.getString("http.method_get_not_supported");        if (protocol.endsWith("1.1")) {            resp.sendError(405, msg);        } else {            resp.sendError(400, msg);        }    }    protected long getLastModified(HttpServletRequest req) {        return -1L;    }    protected void doHead(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        if (DispatcherType.INCLUDE.equals(req.getDispatcherType())) {            this.doGet(req, resp);        } else {            NoBodyResponse response = new NoBodyResponse(resp);            this.doGet(req, response);            response.setContentLength();        }    }    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        String protocol = req.getProtocol();        String msg = lStrings.getString("http.method_post_not_supported");        if (protocol.endsWith("1.1")) {            resp.sendError(405, msg);        } else {            resp.sendError(400, msg);        }    }    protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        String protocol = req.getProtocol();        String msg = lStrings.getString("http.method_put_not_supported");        if (protocol.endsWith("1.1")) {            resp.sendError(405, msg);        } else {            resp.sendError(400, msg);        }    }    protected void doDelete(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        String protocol = req.getProtocol();        String msg = lStrings.getString("http.method_delete_not_supported");        if (protocol.endsWith("1.1")) {            resp.sendError(405, msg);        } else {            resp.sendError(400, msg);        }    }    private static Method[] getAllDeclaredMethods(Class
    c) {        if (c.equals(HttpServlet.class)) {            return null;        } else {            Method[] parentMethods = getAllDeclaredMethods(c.getSuperclass());            Method[] thisMethods = c.getDeclaredMethods();            if (parentMethods != null && parentMethods.length > 0) {                Method[] allMethods = new Method[parentMethods.length + thisMethods.length];                System.arraycopy(parentMethods, 0, allMethods, 0, parentMethods.length);                System.arraycopy(thisMethods, 0, allMethods, parentMethods.length, thisMethods.length);                thisMethods = allMethods;            }            return thisMethods;        }    }    protected void doOptions(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        Method[] methods = getAllDeclaredMethods(this.getClass());        boolean ALLOW_GET = false;        boolean ALLOW_HEAD = false;        boolean ALLOW_POST = false;        boolean ALLOW_PUT = false;        boolean ALLOW_DELETE = false;        boolean ALLOW_TRACE = true;        boolean ALLOW_OPTIONS = true;        Class clazz = null;        try {            clazz = Class.forName("org.apache.catalina.connector.RequestFacade");            Method getAllowTrace = clazz.getMethod("getAllowTrace", (Class[])null);            ALLOW_TRACE = (Boolean)getAllowTrace.invoke(req, (Object[])null);        } catch (NoSuchMethodException | SecurityException | IllegalAccessException | IllegalArgumentException | InvocationTargetException | ClassNotFoundException var14) {            ;        }        for(int i = 0; i < methods.length; ++i) {            Method m = methods[i];            if (m.getName().equals("doGet")) {                ALLOW_GET = true;                ALLOW_HEAD = true;            }            if (m.getName().equals("doPost")) {                ALLOW_POST = true;            }            if (m.getName().equals("doPut")) {                ALLOW_PUT = true;            }            if (m.getName().equals("doDelete")) {                ALLOW_DELETE = true;            }        }        String allow = null;        if (ALLOW_GET) {            allow = "GET";        }        if (ALLOW_HEAD) {            if (allow == null) {                allow = "HEAD";            } else {                allow = allow + ", HEAD";            }        }        if (ALLOW_POST) {            if (allow == null) {                allow = "POST";            } else {                allow = allow + ", POST";            }        }        if (ALLOW_PUT) {            if (allow == null) {                allow = "PUT";            } else {                allow = allow + ", PUT";            }        }        if (ALLOW_DELETE) {            if (allow == null) {                allow = "DELETE";            } else {                allow = allow + ", DELETE";            }        }        if (ALLOW_TRACE) {            if (allow == null) {                allow = "TRACE";            } else {                allow = allow + ", TRACE";            }        }        if (ALLOW_OPTIONS) {            if (allow == null) {                allow = "OPTIONS";            } else {                allow = allow + ", OPTIONS";            }        }        resp.setHeader("Allow", allow);    }    protected void doTrace(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        String CRLF = "\r\n";        StringBuilder buffer = (new StringBuilder("TRACE ")).append(req.getRequestURI()).append(" ").append(req.getProtocol());        Enumeration reqHeaderEnum = req.getHeaderNames();        while(reqHeaderEnum.hasMoreElements()) {            String headerName = (String)reqHeaderEnum.nextElement();            buffer.append(CRLF).append(headerName).append(": ").append(req.getHeader(headerName));        }        buffer.append(CRLF);        int responseLength = buffer.length();        resp.setContentType("message/http");        resp.setContentLength(responseLength);        ServletOutputStream out = resp.getOutputStream();        out.print(buffer.toString());        out.close();    }    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);        }    }    private void maybeSetLastModified(HttpServletResponse resp, long lastModified) {        if (!resp.containsHeader("Last-Modified")) {            if (lastModified >= 0L) {                resp.setDateHeader("Last-Modified", lastModified);            }        }    }    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("non-HTTP request or response");        }        this.service(request, response);    }}

    
           
   
        
            
        
   
   
demo4...

package com.learn.web.servlet;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet("/demo3")public class ServletDemo3 extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        System.out.println("doGet....");    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        System.out.println("doPost...");    }}

 

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