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  • javaweb-maven学习总结

    链接【https://github.com/Davis-Samuel/JavaWeb-order】

    1.准备

    创建JavaWeb父工程

    • 添加Servlet和servlet-jsp的依赖：

      <dependencies>
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>3.1.0</version>
      <scope>provided</scope>
    </dependency>
    
  <dependency>
      <groupId>javax.servlet.jsp</groupId>
      <artifactId>javax.servlet.jsp-api</artifactId>
      <version>2.2.1</version>
      <scope>provided</scope>
    </dependency> 
    
<dependency>
  <groupId>javax.servlet.jsp</groupId>
    <artifactId>jsp-api</artifactId>
    <version>2.2</version>
    <scope>provided</scope>
</dependency>
    
<dependency> <!--jsp表达式的依赖-->
    <groupId>javax.servlet.jsp.jstl</groupId>
    <artifactId>jstl-api</artifactId>
    <version>1.2</version>
</dependency>
    
<dependency> <!--jsp表达式的依赖的-->
    <groupId>taglibs</groupId>
    <artifactId>standard</artifactId>
    <version>1.1.2</version>
</dependency>
    
    <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
            <scope>provided</scope>
        </dependency>

  </dependencies>

    创建Javaweb子工程(servlet-01)

    • 添加，Java和resource文件夹。

    • 添加com.it.helloservlet包，添加HelloServlet类：

      package com.it.servlet;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class HelloServlet extends HttpServlet{
//    由于二者只是get，post请求方式不同，所以可以互相调用，业务逻辑都一样。
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         System.out.println("join in doGet");
//响应流 ServletOutputStream outputStream = resp.getOutputStream();
        PrintWriter writer = resp.getWriter();  
        writer.print("hello");
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
}

    • 换web.xml：

      <?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                      http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
  version="3.0"
  metadata-complete="true">

<!--注册servlet-->
    <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.it.servlet.HelloServlet</servlet-class>
    </servlet>
<!--servlet请求路径-->
    <servlet-mapping>
        <servlet-name>hello</servlet-name >
        <!--       路径可以写为 <url-pattern>*.do</url-pattern> , do可以换成别的，固有的映射路径被访问优先级最高-->
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

</web-app>

    • 配置Tomcat：image-20200216104257161image-20200216104444266

    • 如果是因为资源导出有问题，就在pom.xml中添加：

      <!--在build中配置resources，来防止我们资源导出失败的问题-->
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>

            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

    创造一个error

    • com.it.servlet中，new一个ErrorServlet类：

      package com.it.servlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class ErrorServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        修改格式为text/html的页面编码，变为utf-8
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        PrintWriter writer = resp.getWriter();
        writer.print("<h1>Error 404 </h1>");
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
}

    • web.xml中添加：

          <servlet>
        <servlet-name>error</servlet-name>
        <servlet-class>com.it.servlet.ErrorServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>error</servlet-name >
<!--        /通配符*，后面不管是什么，都执行error-->
        <url-pattern>/*</url-pattern>
    </servlet-mapping>

    2.ServletContext

    模块servlet-02

    • 配置与模块一，一样。修改tomcat，用那个servlet就加那个servlet：image-20200216121300790

    • 简单使用servletContext代码:

      package com.it.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class HelloServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        String name = "111";
        //将name存进了servletContext
        servletContext.setAttribute("name",name);
        
/*     使用  ： new一个类，编写web.xml
    ServletContext servletContext = this.getServletContext();
    由object强转为String
    String name = (String) servletContext.getAttribute(name);
    可以sout也可以resp.getWrite().print("name = " + name);
*/
    }
}

    • 获得初始化参数image-20200219161820199

    • 请求转发image-20200219162720165

    • 在maven中，Java文件和resource文件运行后都在target里面的classes里面，也叫classpath路径。image-20200219163645175

    • 读资源文件文件db.properties：image-20200219165806186

    • 看HttpServletRespones和HttpServletRequest源码，里面有很多方法，设置状态(300,404...)，设置响应头，响应状态码等等等。

    3.Response

    模块servlet-03-response

    • 新建了一个模块，需要修改tomcat的配置

    常见应用

    向浏览器输出信息

    //字节 ServletOutputStream outputStream = resp.getOutputStream()       		  outputStream.writer("hello");
//非字节。PrintWriter writer = resp.getWriter();  writer.writer("hello");

    输入路径回车下载文件。

    • 图片在resource文件中image-20200219182212528

    • image-20200219184154767

    • FileServlet.java：

      package com.it.servlet;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URL;
import java.net.URLEncoder;

public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取下载的路径,右键文件 → copy path → absolute path
        String realPath = "D:\MY\已安装\Java开发\Java.IDEA.Maven\Java.IDEA.Maven程序\JavaWeb\servlet-03-response\src\main\resources\哈哈哈.png";
        System.out.println("下载的文件路径" + realPath);
        //下载的文件名 "获取路径之后的第一位所以+1，第一位就是文件名"
        String fileName = realPath.substring(realPath.lastIndexOf("\") + 1);
        //将图片设置成浏览器可以支持，加入中文文件名的编码
        resp.setHeader("Content-Disposition","attachment;filename=" + URLEncoder.encode(fileName,"UTF-8"));
        //获取下载文件的输入流
        FileInputStream in = new FileInputStream(realPath);
        //创建缓冲区
        int len=0;
        byte[] buffer = new byte[1024];
        //获取输出流对象
        ServletOutputStream out = resp.getOutputStream();
        //用输入流写道缓冲区，再写入客户端
        while ((len=in.read(buffer))>0){
            out.write(buffer,0,len);
        }
        //关闭
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

    • web.xml：

      <?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                      http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         version="3.0"
         metadata-complete="true">
  <!--注册servlet-->
  <servlet>
    <servlet-name>down</servlet-name>
    <servlet-class>com.it.servlet.FileServlet</servlet-class>
  </servlet>
  <!--servlet请求路径-->
  <servlet-mapping>
    <servlet-name>down</servlet-name >
    <!--       路径可以写为 <url-pattern>*.do</url-pattern> , do可以换成别的。固有的映射路径被访问优先级最高-->
    <url-pattern>/down</url-pattern>
  </servlet-mapping>
</web-app>

    实现验证码+数字图片+随机数

    int r = (int) (Math.random()*9); //生成0到9随机的数字

    • image-20200219190546544

    • image-20200219190708206

    重定向

    • protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.sendRedirect("/down");
    }

    • 在web.xml：

       <!--注册servlet-->
  <servlet>
    <servlet-name>down</servlet-name>
    <servlet-class>com.it.servlet.FileServlet</servlet-class>
  </servlet>
  <!--servlet请求路径-->
  <servlet-mapping>
    <servlet-name>down</servlet-name >
    <!--       路径可以写为 <url-pattern>*.do</url-pattern> , do可以换成别的。固有的映射路径被访问优先级最高-->
    <url-pattern>/down</url-pattern>
  </servlet-mapping>



  <servlet>
    <servlet-name>redirect</servlet-name>
    <servlet-class>com.it.servlet.FileServlet</servlet-class>
  </servlet>
  <!--servlet请求路径-->
  <servlet-mapping>
    <servlet-name>redirect</servlet-name >
    <!--       路径可以写为 <url-pattern>*.do</url-pattern> , do可以换成别的。固有的映射路径被访问优先级最高-->
    <url-pattern>/redirect</url-pattern>
  </servlet-mapping>

    • 在浏览器中输入/redirect，就会跳转到/down中。

    3.Request

    模块servlet-04-request

    常见应用

    获取前端请求参数，并请求转发

    • image-20200220191657671
    • image-20200220201134603

    4.Cookie

    • image-20200220215300479

    5.Session

    模块session

    • 在Session类中使用保存，在GetSession类中取得。

    • Session.java：

      package com.it.session;
import com.it.pojo.Person;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
public class Session extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //编码
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        //得到session
        HttpSession session = req.getSession();
        //向session存东西,可以存对象
        session.setAttribute("name",new Person("lisi",10));
        //得到session的id
        String id = session.getId();
        //判断session是不是新建的
        if (session.isNew()){
            resp.getWriter().write("创建成功" + id);
        }else {
            resp.getWriter().write("已经存在" + id);
        }
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

    • GetSession.java：

      package com.it.session;
import com.it.pojo.Person;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
public class GetSession extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");

        HttpSession session = req.getSession();
        Person name = (Person)session.getAttribute("name");
        System.out.println(name.toString());
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

    • web.xml：

      <?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                      http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         version="3.0"
         metadata-complete="true">
  <servlet>
    <servlet-name>getSession</servlet-name>
    <servlet-class>com.it.session.GetSession</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>getSession</servlet-name >
    <url-pattern>/getSession</url-pattern>
  </servlet-mapping>

  <servlet>
    <servlet-name>session</servlet-name>
    <servlet-class>com.it.session.Session</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>session</servlet-name >
    <url-pattern>/session</url-pattern>
  </servlet-mapping>

</web-app>

    6.JSP

    模块jsp

    • 表达式：

      <%= 变量或者表达式%>  <%= new java.util.Date()%>

    • jsp脚本片段：image-20200221145938749

    • image-20200221152627647

    • image-20200221155150633

    • ${ }:也是输出

    • image-20200221155357569

    • 导包：

      在最上面 <%@ page import="java.util.*"%>  alt+回车

    • image-20200221162541687

    • image-20200221163844335

    九大内置对象四大作用域

    • PageContext 存东西

    • Request 存东西

    • Response

    • Session 存东西

    • Application 【SerlvetContext】 存东西

    • config 【SerlvetConfig】

    • out

    • page ，不用了解

    • exception

    • pageContext.setAttribute("name1","秦疆1号"); //保存的数据只在一个页面中有效
request.setAttribute("name2","秦疆2号"); //保存的数据只在一次请求中有效，请求转发会携带这个数据
session.setAttribute("name3","秦疆3号"); //保存的数据只在一次会话中有效，从打开浏览器到关闭浏览器
application.setAttribute("name4","秦疆4号");  //保存的数据只在服务器中有效，从打开服务器到关闭服务器

      request：客户端向服务器发送请求，产生的数据，用户看完就没用了，比如：新闻，用户看完没用的！

      session：客户端向服务器发送请求，产生的数据，用户用完一会还有用，比如：购物车；

      application：客户端向服务器发送请求，产生的数据，一个用户用完了，其他用户还可能使用，比如：聊天数据；

    JSP标签、JSTL标签、EL表达式

    • EL表达式：获取数据，执行运算，获取web开发常用对象

    • JSP标签：

      <%--jsp:include--%>

<%--
相当于：http://localhost:8080/jsptag.jsp?name=kuangshen&age=12
--%>

<jsp:forward page="/jsptag2.jsp">
    <jsp:param name="name" value="kuangshen"></jsp:param>
    <jsp:param name="age" value="12"></jsp:param>
</jsp:forward>

    • JSTL表达式：

    • IF语句

      <head>
    <title>Title</title>
</head>
<body>


<h4>if测试</h4>

<hr>

<form action="coreif.jsp" method="get">
    <%--
    EL表达式获取表单中的数据
    ${param.参数名}
    --%>
    <input type="text" name="username" value="${param.username}">
    <input type="submit" value="登录">
</form>

<%--判断如果提交的用户名是管理员，则登录成功--%>
<c:if test="${param.username=='admin'}" var="isAdmin">
    <c:out value="管理员欢迎您！"/>
</c:if>

<%--如果不是管理员，自闭合标签--%>
<c:out value="${isAdmin}"/>

</body>

    • choose when语句：

      <body>

<%--定义一个变量score，值为85--%>
<c:set var="score" value="55"/>

<c:choose>
    <c:when test="${score>=90}">
        你的成绩为优秀
    </c:when>
    <c:when test="${score>=80}">
        你的成绩为一般
    </c:when>
    <c:when test="${score>=70}">
        你的成绩为良好
    </c:when>
    <c:when test="${score<=60}">
        你的成绩为不及格
    </c:when>
</c:choose>

</body>

    • foreach语句：

      <%

    ArrayList<String> people = new ArrayList<>();
    people.add(0,"张三");
    people.add(1,"李四");
    people.add(2,"王五");
    people.add(3,"赵六");
    people.add(4,"田六");
    request.setAttribute("list",people);
%>


<%--
var , 每一次遍历出来的变量
items, 要遍历的对象
begin,   哪里开始
end,     到哪里
step,   步长
--%>
<c:forEach var="people" items="${list}">
    <c:out value="${people}"/> <br>
</c:forEach>

<hr>

<c:forEach var="people" items="${list}" begin="1" end="3" step="1" >
    <c:out value="${people}"/> <br>
</c:forEach>

    7.Filter

    模块filter

    • 创建一个ServletFilter类：

      package com.it.filter;
import javax.servlet.*;
import java.io.IOException;

public class ServletFilter implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("程序创建");
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=UTF-8");

        System.out.println("doFilter执行前");
        chain.doFilter(request,response); //让请求继续往下走，必须写，如果不写就停止了
        System.out.println("doFilter执行后");
    }

    public void destroy() {
        System.out.println("程序摧毁");
    }
}

    • 创建一个Servlet类：

      package com.it.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class Servlet extends HttpServlet {


    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("你好呀世界");
    }

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

    • web.xml：

      <?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                      http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         version="3.0"
         metadata-complete="true">
  <servlet>
    <servlet-name>servlet</servlet-name>
    <servlet-class>com.it.servlet.Servlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>servlet</servlet-name >
    <url-pattern>/servlet</url-pattern>
  </servlet-mapping>
  
  <filter>
    <filter-name>filter</filter-name>
    <filter-class>com.it.filter.ServletFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>filter</filter-name>
      <!--/servlet/* 下的任何请求都会经过过滤器    -->
    <url-pattern>/servlet/*</url-pattern>
  </filter-mapping> 
</web-app>

    8.small-exercises

    • 见idea源码

    • <!--设置首页欢迎页为login.jsp-->
    <welcome-file-list>
        <welcome-file>login.jsp</welcome-file>
    </welcome-file-list>

<!-- 默认session过期时间  -->
    <session-config>
        <session-timeout>30</session-timeout>
    </session-config>
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  • 原文地址：https://www.cnblogs.com/DavisSamuel/p/12442149.html
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