Servlet 在 JSP 里到底干什么

JSP 负责显示页面给人看Servlet 负责干活后台处理核心作用4 件事接收浏览器发来的请求、获取参数表单提交、url 传参做业务处理判断逻辑、调用数据库查 / 增删改把处理完的数据存起来传给 JSP 页面跳转页面请求转发 / 重定向 跳到 JSP完整流程一定要懂浏览器 → 访问 Servlet 地址Servlet 拿到表单数据Servlet 处理数据Servlet 把数据存入request域Servlet转发到 JSPJSP 取出数据生成 HTML 返回浏览器⚠️ 两个跳转区别考试高频请求转发forwardrequest.getRequestDispatcher(/xxx.jsp).forward(request,response);地址栏不变共享 request 数据✅JSP 能拿到 setAttribute 存的数据是服务器内部跳转2.重定向sendRedirectresponse.sendRedirect(xxx.jsp);地址栏会变不共享 request 数据❌JSP 拿不到 request 存的值浏览器重新发一次新请求要把数据传给 JSP优先用转发 forward二.完整 Java 代码 MyServlet.javaimport java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; //方式1注解配置新版本不用写web.xml //WebServlet(urlPatterns /myServlet) public class MyServlet extends HttpServlet { //处理GET请求 Override public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1. 获取浏览器传过来的参数参数名myName String myName request.getParameter(myName); //2. 设置响应编码防止中文乱码【考试高频】 response.setContentType(text/html;charsetgb2312); //清除浏览器缓存课本写的 response.setHeader(Pragma,No‑cache); response.setDateHeader(Expires,0); response.setHeader(Cache‑Control,no‑cache); //3. 拿到输出流向浏览器写html页面 PrintWriter out response.getWriter(); out.println(html); out.println(headtitle一个简单的Servlet程序/title/head); out.println(body); out.println(h1一个简单的Servlet程序/h1); out.println(pmyName 您好欢迎访问/p); out.println(/body); out.println(/html); out.flush(); //把缓冲区数据推送出去 } //处理POST请求 Override public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //post直接调用doGet共用业务代码 this.doGet(request,response); } }三.方式 Aweb.xml 配置老式配置考试必考?xml version1.0 encodingUTF‑8? web‑app !-- 1.声明Servlet给类起逻辑名字 -- servlet servlet‑nameMyServlet/servlet‑name !-- 写完整包名.类名 -- servlet‑classcom.MyServlet/servlet‑class !-- 【拓展初始化参数】 -- init‑param param‑namenumber/param‑name param‑value1000/param‑value /init‑param !-- 【拓展启动优先级数字越小服务器启动越早加载】 -- load‑on‑startup10/load‑on‑startup /servlet !-- 2.Servlet映射访问路径浏览器输入这个地址访问 -- servlet‑mapping servlet‑nameMyServlet/servlet‑name url‑pattern/myServlet/url‑pattern /servlet‑mapping /web‑app浏览器访问地址http://localhost:8080/项目名/myServlet?myName张三?myName张三就是 get 方式传参数request.getParameter(myName)拿到 张三四、方式 B注解配置WebServlet现代开发不用 web.xml直接写在 Servlet 类上面替代 web.xml 全部配置import javax.servlet.annotation.WebServlet; //urlPatterns 访问路径多个路径可以写 {/a,/b} WebServlet(urlPatterns /myServlet, loadOnStartup -1, //加载顺序‑1代表第一次访问才创建 initParams {WebInitParam(namenumber,value1000)} ) public class MyServlet extends HttpServlet{ //doGet doPost方法同上 }Filter 过滤器完整整理课本案例Filter 过滤器请求到达 Servlet/JSP 之前先经过过滤器拦截处理可以做编码统一、登录校验、访问统计、过滤敏感词。 过滤器链多个过滤器按顺序执行chain.doFilter()把请求传给下一个过滤器 / 目标资源。一、Filter 核心 3 个方法实现 Filter 接口必须重写public interface Filter{ //①init()过滤器创建的时候执行【只执行1次】做初始化读取init‑param参数 void init(FilterConfig filterConfig); //②doFilter()每一次请求进来都会执行核心过滤方法 void doFilter(ServletRequest request,ServletResponse response,FilterChain chain); //③destroy()服务器关闭销毁过滤器【只执行1次】释放资源 void destroy(); }二、基础过滤器 MyFilter 完整代码例 6‑2import java.io.IOException; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; public class MyFilter implements Filter { //初始化服务器启动过滤器对象创建执行一次 Override public void init(FilterConfig fConfig) throws ServletException { //初始化处理读取配置的初始化参数 } //核心过滤每次请求都跑这里 Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // 请求到达资源之前写【预处理代码】例如设置编码 //放行向下传递请求执行下一个过滤器/目标Servlet/JSP chain.doFilter(request, response); // 服务器处理完资源之后回来执行【后处理代码】 } //销毁服务器关闭执行一次释放资源 Override public void destroy() { //释放资源 } }三、配置过滤器两种方式方式 1web.xml 配置考试重点老式!-- 1.声明过滤器 -- filter filter‑nameMyFilter/filter‑name !-- 完整包名.类名 -- filter‑classcom.lyq.MyFilter/filter‑class !-- 初始化参数可选 -- init‑param param‑namexxx/param‑name param‑value123/param‑value /init‑param /filter !--2.过滤器映射哪些url要被这个过滤器拦截 -- filter‑mapping filter‑nameMyFilter/filter‑name !--拦截路径 /* 拦截全部请求/index.jsp只拦截首页 -- url‑pattern/MyFilter/url‑pattern /filter‑mapping方式 2注解配置现代开发替代 web.xmlimport javax.servlet.annotation.WebFilter; //urlPatterns拦截路径/*代表拦截所有访问 WebFilter(urlPatterns /*) public class MyFilter implements Filter{ //三个方法同上 }四、课本案例网站访问计数器 CountFilter例 6‑4功能统计网站访客初始访问数量 5000存到ServletContext(application)所有页面共享。1.CountFilter.java 代码import java.io.IOException; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServletRequest; public class CountFilter implements Filter { private int count; //访问计数 Override public void init(FilterConfig filterConfig) throws ServletException { //读取web.xml配置的初始化参数count String param filterConfig.getInitParameter(count); count Integer.valueOf(param); //字符串转数字 } Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { count; //访问数1 //ServletRequest转成HttpServletRequest HttpServletRequest req (HttpServletRequest) request; //拿到全局ServletContext对应JSP的application对象 ServletContext context req.getSession().getServletContext(); //把计数存入全局域所有页面共享 context.setAttribute(count,count); //放行访问目标页面 chain.doFilter(request, response); } Override public void destroy() { } }2.web.xml 配置 CountFilterfilter filter‑nameCountFilter/filter‑name filter‑classcom.lyq.CountFilter/filter‑class !--初始化参数初始访问数5000 -- init‑param param‑namecount/param‑name param‑value5000/param‑value /init‑param /filter !--拦截index.jsp首页 -- filter‑mapping filter‑nameCountFilter/filter‑name url‑pattern/index.jsp/url‑pattern /filter‑mapping3.index.jsp 页面取出计数显示body h2欢迎光临br 您是本站的第【${applicationScope.count}】位访客 /h2 /body五、字符编码过滤器开发最常用解决中文乱码WebFilter(/*) //拦截全部请求 public class EncodingFilter implements Filter{ Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { //统一设置请求编码 request.setCharacterEncoding(utf‑8); //统一设置响应编码 response.setContentType(text/html;charsetutf‑8); //放行 chain.doFilter(request,response); } Override public void init(FilterConfig filterConfig) {} Override public void destroy() {} }字符编码过滤器 添加图书 Servlet 案例整理课本例 6‑5一、CharacterFilter 字符编码过滤器作用统一设置请求、响应编码解决中文乱码编码写在 web.xml 初始化参数代码不写死 UTF‑8灵活修改。1. CharacterFilter.java 完整代码import java.io.IOException; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; public class CharacterFilter implements Filter { private String encoding; //保存编码从web.xml读取 Override public void init(FilterConfig filterConfig) throws ServletException { //读取web.xml里面 init‑param 的encoding参数 encoding filterConfig.getInitParameter(encoding); } Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { //判断编码参数不为空才设置 if(encoding ! null){ request.setCharacterEncoding(encoding); response.setContentType(text/html;charsetencoding); } //放行交给下一个过滤器/Servlet chain.doFilter(request, response); } Override public void destroy() { encoding null; } }2. web.xml 配置过滤器!--声明过滤器-- filter filter‑nameCharacterFilter/filter‑name filter‑classcom.lyq.CharacterFilter/filter‑class !--初始化参数编码UTF‑8-- init‑param param‑nameencoding/param‑name param‑valueUTF‑8/param‑value /init‑param /filter !--过滤器映射/*拦截全部请求-- filter‑mapping filter‑nameCharacterFilter/filter‑name url‑pattern/*/url‑pattern /filter‑mapping考点/*代表拦截项目下所有资源jsp、servlet、html所有请求自动设置 UTF‑8 编码。二、AddServlet处理添加图书Servlet功能表单 post 提交图书编号、名称、作者、价格Servlet 接收参数输出。 小技巧doGet()里面直接调用doPost(request,response)GET、POST 请求都走 doPost 代码不用写两份业务。1. AddServlet.javaimport java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class AddServlet extends HttpServlet { private static final long serialVersionUID 1L; //get请求直接调用post方法 Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request, response); } Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { PrintWriter out response.getWriter(); //获取表单提交参数name属性对应 String id request.getParameter(id); String name request.getParameter(name); String author request.getParameter(author); String price request.getParameter(price); //输出结果页面 out.print(h2图书信息添加成功/h2hr); out.print(图书编号id br/); out.print(图书名称name br/); out.print(作者author br/); out.print(价格price br/); out.flush(); //刷新缓冲区 out.close(); //关闭输出流 } }2. web.xml 配置 AddServletservlet servlet‑nameAddServlet/servlet‑name servlet‑classcom.lyq.AddServlet/servlet‑class /servlet servlet‑mapping servlet‑nameAddServlet/servlet‑name url‑pattern/AddServlet/url‑pattern /servlet‑mapping3. index.jsp 表单页面输入图书信息% page languagejava contentTypetext/html; charsetUTF‑8 pageEncodingUTF‑8% html body form actionAddServlet methodpost table aligncenter border1 width350 tr td colspan2 aligncenter h2添加图书信息/h2 /td /tr tr td alignright图书编号/td tdinput typetext nameid/td /tr tr td alignright图书名称/td tdinput typetext namename/td /tr tr td alignright作nbsp;nbsp;nbsp;nbsp;者/td tdinput typetext nameauthor/td /tr tr td alignright价nbsp;nbsp;nbsp;nbsp;格/td tdinput typetext nameprice/td /tr tr td colspan2 aligncenter input typesubmit value添 加 /td /tr /table /form /body /htmlServlet 监听器在线用户统计案例整理https://www.doubao.com/thread/xiYECyrPDZSaWWo2F