JSP原理
瀏覽器向服務器發送請求，不管訪問什麼資源，其實都是在訪問Servlet
JSP 本質也是Servlet，實現了HttpServlet
- 判斷請求
- 內置對象(pageContext,session,application,config,out,page,request,response)
- 輸出頁面前增加的代碼
- 在JSP中，JAVA代碼會原封不動的輸出，HTML會被轉為
out.write("<html>");的格式輸出
基礎語法
引入JSTL表達式依賴包javax.servlet.jsp.jstl 和standard標籤庫
<dependency>
<groupId>javax.servlet.jsp.jstl</groupId>
<artifactId>jstl-api</artifactId>
<version>1.2</version>
</dependency>
<dependency>
<groupId>taglibs</groupId>
<artifactId>standard</artifactId>
<version>1.1.2</version>
</dependency>表達式：<%= 變量或表達式 %>
用來將程序輸出到客户端
<%= new java.util.Date()%> //Tue Nov 23 21:19:01 CST 2021腳本片段：<% java代碼 %>
<% out.println("test");%>代碼嵌入HTML元素： ${}
<% for(int i=0;i<10;i++){%>
<p>${i}</p>
<% }%>聲明：<%! %>
JSP的聲明，會被編譯到JSP生成的類中；其他會生成到_jspService方法中
<%!
static {
System.out.println("test");
}
%>註釋：<%-- 註釋 --%>
<%-- JSP的註釋，不會在客户端顯示 --%>指令：<%@ page %> <%@ include %>
<%@ page errorPage="error/500.jsp" %> //指定500頁面標籤 <jsp:include />
<jsp:include page="/common/header.jsp"/><%@include %>和<jsp:include /> 的區別：1會合並頁面 2不會
內置對象
- PageContext
- Request
- Response
- Session
- Application (ServletContext)
- Config (ServletConfig)
- out
- page
- Exception
<%
pageContext.setAttribute("name1","Name1");//在一個頁面中有效
request.setAttribute("name2","Name2"); //在一次請求中有效
session.setAttribute("name3","Name3"); //在一次對話中有效
application.setAttribute("name4","Name4");//在服務器一次開關中有效
%>
<%
//從底層到高層（作用域）：page > request > session > application
//雙親委派機制：
String name1 = (String) pageContext.findAttribute("name1");
String name2 = (String) pageContext.findAttribute("name2");
String name3 = (String) pageContext.findAttribute("name3");
String name4 = (String) pageContext.findAttribute("name4");
%>
<h1>${name1}</h1>
<h2>${name2}</h2>
<h3>${name3}</h3>
<h4>${name4}</h4>EL表達式
EL表達式：獲取數據，執行運算，獲取web開發的常用對象
<jsp:forward page="/test.jsp">
<jsp:param name="name" value="xiaoma"/>
<jsp:param name="phone" value="13511112222"/>
</jsp:forward>
EL表達式獲取參數：<%= request.getParameter("name")%>
EL表達式獲取表單數據：${param.參數名}JSTL表達式
JSP標籤集貨，封裝了JSP應用的通用核心功能
-
引用核心標籤庫：
<%@taglib prefix="c" uri="http://java.sun.com/jstl/core" %> -
常用標籤
<%--判斷表單參數--%> <c:if test="${param.name} == 'admin'"> <c:out value="登錄成功"></c:out> </c:if> <%--其他--%> <c:choose> <c:when> <c:set> <c:forEach var="item" items="${list}">
JavaBean
一般用來做數據庫字段做映射ORM（對象關係映射）：表 -> 類，字段 -> 屬性，行記錄 -> 對象
- 必須有一個無參構造
- 屬性必須私有化
- 必須有對應的get/set方法
class People {
private int id;
private String name;
private int age;
}### 過濾器 Filter
- 過濾器中的代碼，在過濾特定請求時都會執行
- 必須要讓過濾器繼續通行
cn/itxiaoma/filter/TestFilter.java
package cn.itxiaoma.filter;
import javax.servlet.*;
import java.io.IOException;
public class TestFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("過濾器開始");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
System.out.println("過濾器執行前...");
chain.doFilter(request, response);//讓過濾器繼續執行
System.out.println("過濾器執行後...");
}
@Override
public void destroy() {
System.out.println("過濾器銷燬");
}
}src/main/webapp/WEB-INF/web.xml
<filter>
<filter-name>TestFilter</filter-name>
<filter-class>cn.itxiaoma.filter.TestFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>TestFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>監聽器 Listener
public class TestListener implements HttpSessionListener {
...
}<!--註冊監聽器-->
<listener>
<listener-class>cn.itxiaoma.listener.TestListener</listener-class>
</listener>Filter實現權限攔截
src/main/webapp/login.jsp
<form action="servlet/login" method="post">
<input type="text" name="username"/>
<input type="submit" value="Login">
</form>src/main/webapp/WEB-INF/web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0"
metadata-complete="true">
<servlet>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>cn.itxiaoma.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/servlet/login</url-pattern>
</servlet-mapping>
<filter>
<filter-name>SysFilter</filter-name>
<filter-class>cn.itxiaoma.filter.SysFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>SysFilter</filter-name>
<url-pattern>/sys/*</url-pattern>
</filter-mapping>
</web-app>cn/itxiaoma/servlet/LoginServlet.java
package cn.itxiaoma.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 LoginServlet extends HttpServlet {
//get和post只是請求實現的不同方式，業務邏輯一樣，因此可以互相調用
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String username = req.getParameter("username");
if (username.equals("admin")) {
req.getSession().setAttribute("USER_SESSION", req.getSession().getId());
resp.sendRedirect("/sys/success.jsp");
}else{
resp.sendRedirect("/error.jsp");
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}cn/itxiaoma/filter/SysFilter.java
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse resp = (HttpServletResponse) response;
if (req.getSession().getAttribute("USER_SESSION") == null) {
resp.sendRedirect("/error.jsp");
}
chain.doFilter(request, response);
}