JavaWeb学习+实例代码

前言

会根据学习进度持续更新，觉得写的不错的可以收藏跟进。不足之处可以评论
编辑器：IDEA
JDK：11
Tomcat：9.0.54
数据库：MySQL 8.0

前言
一、 Servlet配置
二、 Servlet应用
- 1. 处理数据请求
- - 1.1. 超链接
  - 1.2. Form表单
- 2. 重定向与请求转发
- - 2.1. 重定向
  - 2.2. 请求转发
  - 2.3 对数据的存取
  - 2.4 重定向与请求转发区别
三、 Servlet接口
- 1. Config接口
- 2. Context接口
- 3. Request接口
- 4. Response接口
四、会话跟踪
- 1. cookie
- 2. Session
- 3.URL重写技术应用
- 4. 隐藏表单域
五、 JSP
- 1. JSP基础
- - 1.1 JSP与Servlet
  - 1.2. JSP基本结构

一、 Servlet配置

声明Servlet

3.0以后以注解为准

@WebServlet(name = "类名，可以不写",urlPatterns = "/类名url")

二、 Servlet应用 1. 处理数据请求

请求数据方式：超链接和Form表单

1.1. 超链接

超链接一般用于获取/查询资源，属于get类型。数据会依附在URL之后，以？分割URL和传输数据，参数之间以&相连
- 缺点：安全性差，长度限制

1.2. Form表单

Form用于更新资源信息，默认使用GET类型，多使用POST类型。由于POST请求类型理论上没有数据大小限制，可用表单来传比较大的数据

2. 重定向与请求转发 2.1. 重定向

用HttpServletResponse对象的sendRedirect()实现

可以指定到任意页面

实现类

@WebServlet(name = "RedirectServlet",urlPatterns = "/RedirectServlet")
public class RedirectServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        resp.sendRedirect("/RedirectTest");
        resp.getWriter().println("redirect test重定向测试");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

测试类

@WebServlet(name = "RedirectTest",urlPatterns = "/RedirectTest")
public class RedirectTest extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        PrintWriter pw = resp.getWriter();
        pw.println("successful成功");
    }

    @Override
    protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

2.2. 请求转发

请求转发不能指定任意地址

实现类如下，测试类为RedirectTest

@WebServlet(name = "ForwardServlet",urlPatterns = "/ForwardServlet")
public class ForwardServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        req.getRequestDispatcher("/RedirectTest").forward(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

Forward与include区别
- Forward以请求页面为主体，请求另一个页面
- include把请求页面发回Servlet再次请求另一个页面，Servlet为主体
- 响应结果都是请求页。

2.3 对数据的存取

重定向不传输数据，请求转发传输数据

实现类

@WebServlet(name = "ForwardAttributeServlet",urlPatterns = "/ForwardAttributeServlet")
public class ForwardAttributeServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        req.setAttribute("objname","jing");
        req.getRequestDispatcher("/ResultTest").forward(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

@WebServlet(name = "RedirectAttributeServletServlet",urlPatterns = "/RedirectAttributeServlet")
public class RedirectAttributeServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        req.setAttribute("objname","jing");
        resp.sendRedirect("/ResultTest");
        resp.getWriter().println("redirect test重定向测试");

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

测试类

@WebServlet(name = "ResultTest",urlPatterns = "/ResultTest")
public class ResultTest extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        PrintWriter pw = resp.getWriter();
        String obj = (String) req.getAttribute("objname");
        pw.println("result");
        pw.println("obj name is "+ obj);
    }

    @Override
    protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

2.4 重定向与请求转发区别三、 Servlet接口 1. Config接口

一个Servlet有一个Config接口

获取参数和对象方法

重写GenericServlet的init()方法,通过初始化init()方法传递过来的ServletConfig对象获取

public void init(ServletConfig config) throws ServletException {
        super.init(config);
        String username = config.getInitParameter("username");
        String password = config.getInitParameter("password");
        System.out.println("账号:"+username+"t密码"+password);
    }

直接调用GenericServlet里的getServletConfig()方法获取 (常用方法)

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    ServletConfig config = getServletConfig();
    String username = config.getInitParameter("username");
    String password = config.getInitParameter("password");
    System.out.println("账号:"+username+"t密码"+password);
}

2. Context接口

获取应用初始化参数，在xml里进行配置，Context会读取这些配置存在ServletContext对象中

实例

public class ContextInitParaServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        ServletContext context = getServletContext();
        String website = context.getInitParameter("website");
        String email = context.getInitParameter("email");
        PrintWriter out = resp.getWriter();
        out.println("jingjiu个人主页地址:" + website + "
");
        out.println("jignjiu邮箱:" + email );
        Enumeration paramNames = context.getInitParameterNames();
        out.println("
");
        while ((paramNames.hasMoreElements())){
            out.println(paramNames.nextElement()+" ");
        }
    }
}

 
        website
        http://jingjiu.itdage.cn/u.html?userid=30
    

    
        email
        lybhlh@163.com

应用域：ServletContext可以理解为容器内的一个共享空间，可以存放应用级别作用域的数据，web组件都可以共享这些数据，数据以键值对形式存在

例子：网站计数

public class ContextAttributeServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        //创建Context对象
        ServletContext context = getServletContext();
        Integer vistedcount = (Integer) context.getAttribute("vistedcount");
        if(vistedcount == null){
            vistedcount = 1;
        }else {
            vistedcount += 1;
        }
        //设置值
        context.setAttribute("vistedcount", vistedcount);
        //创建值
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String date = sdf.format(new Date());
        //输出
        PrintWriter out = resp.getWriter();
        out.println("当前网站被访问次数:"+vistedcount+"");
        out.println("本次访问时间:"+date+"");
    }
}

获取应用信息

public class ContextInfoServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        ServletContext context = getServletContext();
        String contextPath = context.getContextPath();//返回根路径
        String servletcontextname = context.getServletContextName();//servlet设置名称
        String servletInfo = context.getServerInfo();//web容器版本名称
        String version = context.getMajorVersion() + "-" + context.getMajorVersion();//获取API主次版本号
        context.log("自定义日志信息");
        context.log("自定义错误",new Exception("异常堆栈信息"));

        PrintWriter out = resp.getWriter();
        out.println("当前web应用上下文(当前项目)根路径:" + contextPath + "
");
        out.println("当前servlet设置的显示名称:" + servletcontextname + "
");
        out.println("当前web容器名称、版本:" + servletInfo + "
");
        out.println("支持Servlet API主、次版本号:" + version);
    }
}

3. Request接口

部分常用方法

public class RequestLineServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        //获取请求Http的方法
        String method = req.getMethod();
        //获取请求中资源名部分
        String url = req.getRequestURI();
        //获取协议版本号
        String protocol = req.getProtocol();
        //获取请求URL后面查询的字符串
        String queryStr = req.getQueryString();
        //获取当前请求的Servlet路径
        String servletPath = req.getServletPath();
        //获取请求资源所属的web路径
        String contextPath = req.getContextPath();
        String serverName = req.getServerName();
        int serverPort = req.getServerPort();
        String scheme = req.getScheme();
        PrintWriter out = resp.getWriter();
        out.println("获取请求Http的方法:"+ method + "");
        out.println("获取请求中资源名部分:"+ url + "");
        out.println("获取协议版本号:"+ protocol + "");
        out.println("获取请求URL后面查询的字符串:"+ queryStr + "");
        out.println("获取当前请求的Servlet路径:"+ servletPath + "");
        out.println("获取请求资源所属的web路径:"+ contextPath + "");
        out.println("获取网站域名:" + serverName + "");
        out.println("获取端口号:" + serverPort + "");
        out.println("获取请求协议：" + scheme + "");
    }
}

4. Response接口

Http响应报文
- 1xx:表示信息，服务器收到请求，需要请求者继续执行操作
- 2xx:表示请求已经成功被服务器接收
- 3xx:表示需要客户端进一步操作才能完成请求
- 4xx:客户端错误，请求包含语法错误或者无法完成请求
- 5xx:服务器在处理请求过程中有错误或者异常状态发生，也可能服务器意识到无法完成对请求的处理

设置响应头

实例:利用refresh制作一个动态时钟

public class ResponseRefreshServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/heml;charset=utf-8");
        resp.setHeader("Course","JavaWeb");
        resp.setHeader("refresh","1");
        PrintWriter out = resp.getWriter();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        out.println(sdf.format(new Date()));
    }
}

中文输出：setCharacterEncoding()与setContentType()区别
- setCharacterEncoding()只能设置PrintWriter输出流中字符的编码方式，优先权最高
- setContentType()既可以设置PrintWriter输出流中字符的编码方式，也可以设置浏览器接收到这些字符后以什么编码方式来解码
实例:输出一张图片(图片放在webapp文件夹下)

public class OutputStreamServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("image/png");
        ServletContext context = getServletContext();
        InputStream is = context.getResourceAsStream("/image/picture.jpg");
        ServletOutputStream sos = resp.getOutputStream();
        int i = 0;
        while ((i = is.read())!= -1){
            sos.write(i);
        }
    }
}

四、会话跟踪 1. cookie

cookie构造方法需要两个参数
- String类型指定cookie的属性名
- String类型指定属性值

示例cookie unamecookie = new cookie("username","jingjiu");

addcookie()
- 参数为一个cookie对象
- 通过此方法增加"Set-cookie"响应头的方式将cookie对象响应给客户端浏览器，储存在客户端机器上
- 生成的cookie仅在当前浏览器有效
储存在客户端的cookie通过getcookies()方法获取，返回所访问网站的所有cookie的对象数组，遍历该数组可以获得各个cookie对象

实例：

@WebServlet(name = "cookieExampleServlet", urlPatterns = "/cookieExampleServlet")
public class cookieExampleServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");

        int visitedCount = 0;//访问次数
        String lastVisTime = "";//访问时间
        cookie[] cookie = req.getcookies();
        if (cookie != null) {
            for (cookie cookies : cookie) {
                if ("visitedCount".equals(cookies.getName())) {
                    visitedCount = Integer.valueOf(cookies.getValue());
                }
                if ("lastVisTime".equals(cookies.getName())) {
                    lastVisTime = cookies.getValue();
                }
            }
        }
        PrintWriter out = resp.getWriter();
        if (!"".equals(lastVisTime)) {
            out.println("上一次访问时间:" + lastVisTime);
        }
        out.println("第" + (visitedCount + 1) + "次访问此网站");
        cookie visitCountC = new cookie("visitedCount", String.valueOf(visitedCount + 1));
        resp.addcookie(visitCountC);
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-ddHH:mm:ss");
        cookie lastVisTimeC = new cookie("lastVisTime", sdf.format(new Date()));
        resp.addcookie(lastVisTimeC);
    }
}

cookie有存活时间，默认在关闭浏览器时失效。若要长时间保存，使用setMaxAge()方法设置存活时间，保存在磁盘上的cookie称为持久cookie

缺点：

cookie可能被禁用
不同浏览器不能互相访问
可能被用户删除
大小个数受限，单个cookie不能超过4k，一个站点最多保存20个cookie

2. Session

Session使用HttpSession对象实现会话跟踪技术，在服务器端保持会话跟踪。
HttpSession对象会在用户第一次访问服务器时由容器创建，用来保存单个用户访问时的一些信息

实现简单的购物车功能

html




    
    书籍选购



    
        JavaEE应用与开发
    
    
        JavaEE从入门到放弃
    
    
        数据库应用与开发
    
    
        Spring框架

ShoppingCarServlet

@WebServlet(name = "ShoppingCarServlet", urlPatterns = "/ShoppingCarServlet")
public class ShoppingCarServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");

        //获取Session
        HttpSession session = req.getSession();
        Map car = (Map) session.getAttribute("ShopCar");
        if (car == null) {
            car = new HashMap();
        }
        //获取用户选择的书籍信息
        String[] books = req.getParameterValues("book");
        if (books != null && books.length > 0) {
            for (String b : books) {
                //根据书名(map中的key)判断此书是否在购物车
                if (car.get(b) != null) {
                    int num = car.get(b);
                    car.put(b, num + 1);
                } else {
                    car.put(b, 1);
                }
            }
        }
        session.setAttribute("ShopCar",car);
        resp.sendRedirect("ShoppingListServlet");
    }
}

ShoppingListServlet

@WebServlet(name = "cookieExampleServlet", urlPatterns = "/cookieExampleServlet")
public class cookieExampleServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");

        int visitedCount = 0;//访问次数
        String lastVisTime = "";//访问时间
        cookie[] cookie = req.getcookies();
        if (cookie != null) {
            for (cookie cookies : cookie) {
                if ("visitedCount".equals(cookies.getName())) {
                    visitedCount = Integer.valueOf(cookies.getValue());
                }
                if ("lastVisTime".equals(cookies.getName())) {
                    lastVisTime = cookies.getValue();
                }
            }
        }
        PrintWriter out = resp.getWriter();
        if (!"".equals(lastVisTime)) {
            out.println("上一次访问时间:" + lastVisTime);
        }
        out.println("第" + (visitedCount + 1) + "次访问此网站");
        cookie visitCountC = new cookie("visitedCount", String.valueOf(visitedCount + 1));
        resp.addcookie(visitCountC);
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-ddHH:mm:ss");
        cookie lastVisTimeC = new cookie("lastVisTime", sdf.format(new Date()));
        resp.addcookie(lastVisTimeC);
    }
}

3.URL重写技术应用

对应用所有的请求都重写才能将jsessionid ¹维持下来
URL地址必须为动态请求地址

4. 隐藏表单域

可以完全脱离浏览器对cookie的使用限制，在用户无法从页面显示看到隐藏标识的情况下，将标识随请求一起传送给服务器处理，实现会话跟踪。

五、 JSP 1. JSP基础 1.1 JSP与Servlet

JSP是一种服务器端脚本语言，降低了Servlet编写页面的难度，本质上就是一种Servlet

1.2. JSP基本结构

JSP包含3种元素

脚本元素

脚本<%%>
表达式<%=%>
声明<%！%>
注释<%-- --%>

指令元素

<%@page %>导入包，指明输出内容类型，控制Session
<%@include file="文件" %>在页面翻译期间引入另一个文件,新文件不能和当前文件定义同名变量
<%@taglib uri="标签库URI" prefix="标签前缀"%>

动作元素

引入文件
把请求转发到另一个页面
用于查找或者实例化一个JavaBean
用于设置JavaBean的属性
用于输出某个JavaBean的属性

追加的会话标识，服务器通过它来之别跟踪某个用户的访问 ↩︎

JavaWeb学习+实例代码

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