<!doctype html>01 - JavaEE- JSP - EL&JSTL

figure:first-child { margin-top: -20px; }
#write ol, #write ul { position: relative; }
img { max-width: 100%; vertical-align: middle; }
button, input, select, textarea { color: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; font-stretch: inherit; font-size: inherit; line-height: inherit; font-family: inherit; }
input[type="checkbox"], input[type="radio"] { line-height: normal; padding: 0px; }
*, ::after, ::before { box-sizing: border-box; }
#write h1, #write h2, #write h3, #write h4, #write h5, #write h6, #write p, #write pre { width: inherit; }
#write h1, #write h2, #write h3, #write h4, #write h5, #write h6, #write p { position: relative; }
h1, h2, h3, h4, h5, h6 { break-after: avoid-page; break-inside: avoid; orphans: 2; }
p { orphans: 4; }
h1 { font-size: 2rem; }
h2 { font-size: 1.8rem; }
h3 { font-size: 1.6rem; }
h4 { font-size: 1.4rem; }
h5 { font-size: 1.2rem; }
h6 { font-size: 1rem; }
.md-math-block, .md-rawblock, h1, h2, h3, h4, h5, h6, p { margin-top: 1rem; margin-bottom: 1rem; }
.hidden { display: none; }
.md-blockmeta { color: rgb(204, 204, 204); font-weight: 700; font-style: italic; }
a { cursor: pointer; }
sup.md-footnote { padding: 2px 4px; background-color: rgba(238, 238, 238, 0.7); color: rgb(85, 85, 85); border-radius: 4px; cursor: pointer; }
sup.md-footnote a, sup.md-footnote a:hover { color: inherit; text-transform: inherit; text-decoration: inherit; }
#write input[type="checkbox"] { cursor: pointer; width: inherit; height: inherit; }
figure { overflow-x: auto; margin: 1.2em 0px; max-width: calc(100% + 16px); padding: 0px; }
figure > table { margin: 0px !important; }
tr { break-inside: avoid; break-after: auto; }
thead { display: table-header-group; }
table { border-collapse: collapse; border-spacing: 0px; width: 100%; overflow: auto; break-inside: auto; text-align: left; }
table.md-table td { min-width: 32px; }
.CodeMirror-gutters { border-right: 0px; background-color: inherit; }
.CodeMirror { text-align: left; }
.CodeMirror-placeholder { opacity: 0.3; }
.CodeMirror pre { padding: 0px 4px; }
.CodeMirror-lines { padding: 0px; }
div.hr:focus { cursor: none; }
#write pre { white-space: pre-wrap; }
#write.fences-no-line-wrapping pre { white-space: pre; }
#write pre.ty-contain-cm { white-space: normal; }
.CodeMirror-gutters { margin-right: 4px; }
.md-fences { font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; overflow: visible; white-space: pre; background: inherit; position: relative !important; }
.md-diagram-panel { width: 100%; margin-top: 10px; text-align: center; padding-top: 0px; padding-bottom: 8px; overflow-x: auto; }
#write .md-fences.mock-cm { white-space: pre-wrap; }
.md-fences.md-fences-with-lineno { padding-left: 0px; }
#write.fences-no-line-wrapping .md-fences.mock-cm { white-space: pre; overflow-x: auto; }
.md-fences.mock-cm.md-fences-with-lineno { padding-left: 8px; }
.CodeMirror-line, twitterwidget { break-inside: avoid; }
.footnotes { opacity: 0.8; font-size: 0.9rem; margin-top: 1em; margin-bottom: 1em; }
.footnotes + .footnotes { margin-top: 0px; }
.md-reset { margin: 0px; padding: 0px; border: 0px; outline: 0px; vertical-align: top; background: 0px 0px; text-decoration: none; text-shadow: none; float: none; position: static; width: auto; height: auto; white-space: nowrap; cursor: inherit; -webkit-tap-highlight-color: transparent; line-height: normal; font-weight: 400; text-align: left; box-sizing: content-box; direction: ltr; }
li div { padding-top: 0px; }
blockquote { margin: 1rem 0px; }
li .mathjax-block, li p { margin: 0.5rem 0px; }
li { margin: 0px; position: relative; }
blockquote > :last-child { margin-bottom: 0px; }
blockquote > :first-child, li > :first-child { margin-top: 0px; }
.footnotes-area { color: rgb(136, 136, 136); margin-top: 0.714rem; padding-bottom: 0.143rem; white-space: normal; }
#write .footnote-line { white-space: pre-wrap; }
@media print {
body, html { border: 1px solid transparent; height: 99%; break-after: avoid; break-before: avoid; }
#write { margin-top: 0px; padding-top: 0px; border-color: transparent !important; }
.typora-export * { -webkit-print-color-adjust: exact; }
html.blink-to-pdf { font-size: 13px; }
.typora-export #write { padding-left: 32px; padding-right: 32px; padding-bottom: 0px; break-after: avoid; }
.typora-export #write::after { height: 0px; }
@page { margin: 20mm 0px; }
}
.footnote-line { margin-top: 0.714em; font-size: 0.7em; }
a img, img a { cursor: pointer; }
pre.md-meta-block { font-size: 0.8rem; min-height: 0.8rem; white-space: pre-wrap; background: rgb(204, 204, 204); display: block; overflow-x: hidden; }
p > .md-image:only-child:not(.md-img-error) img, p > img:only-child { display: block; margin: auto; }
p > .md-image:only-child { display: inline-block; width: 100%; }
#write .MathJax_Display { margin: 0.8em 0px 0px; }
.md-math-block { width: 100%; }
.md-math-block:not(:empty)::after { display: none; }
[contenteditable="true"]:active, [contenteditable="true"]:focus { outline: 0px; box-shadow: none; }
.md-task-list-item { position: relative; list-style-type: none; }
.task-list-item.md-task-list-item { padding-left: 0px; }
.md-task-list-item > input { position: absolute; top: 0px; left: 0px; margin-left: -1.2em; margin-top: calc(1em - 10px); border: none; }
.math { font-size: 1rem; }
.md-toc { min-height: 3.58rem; position: relative; font-size: 0.9rem; border-radius: 10px; }
.md-toc-content { position: relative; margin-left: 0px; }
.md-toc-content::after, .md-toc::after { display: none; }
.md-toc-item { display: block; color: rgb(65, 131, 196); }
.md-toc-item a { text-decoration: none; }
.md-toc-inner:hover { text-decoration: underline; }
.md-toc-inner { display: inline-block; cursor: pointer; }
.md-toc-h1 .md-toc-inner { margin-left: 0px; font-weight: 700; }
.md-toc-h2 .md-toc-inner { margin-left: 2em; }
.md-toc-h3 .md-toc-inner { margin-left: 4em; }
.md-toc-h4 .md-toc-inner { margin-left: 6em; }
.md-toc-h5 .md-toc-inner { margin-left: 8em; }
.md-toc-h6 .md-toc-inner { margin-left: 10em; }
@media screen and (max-width: 48em) {
.md-toc-h3 .md-toc-inner { margin-left: 3.5em; }
.md-toc-h4 .md-toc-inner { margin-left: 5em; }
.md-toc-h5 .md-toc-inner { margin-left: 6.5em; }
.md-toc-h6 .md-toc-inner { margin-left: 8em; }
}
a.md-toc-inner { font-size: inherit; font-style: inherit; font-weight: inherit; line-height: inherit; }
.footnote-line a:not(.reversefootnote) { color: inherit; }
.md-attr { display: none; }
.md-fn-count::after { content: "."; }
code, pre, samp, tt { font-family: var(--monospace); }
kbd { margin: 0px 0.1em; padding: 0.1em 0.6em; font-size: 0.8em; color: rgb(36, 39, 41); background: rgb(255, 255, 255); border: 1px solid rgb(173, 179, 185); border-radius: 3px; box-shadow: rgba(12, 13, 14, 0.2) 0px 1px 0px, rgb(255, 255, 255) 0px 0px 0px 2px inset; white-space: nowrap; vertical-align: middle; }
.md-comment { color: rgb(162, 127, 3); opacity: 0.8; font-family: var(--monospace); }
code { text-align: left; vertical-align: initial; }
a.md-print-anchor { white-space: pre !important; border-width: initial !important; border-style: none !important; border-color: initial !important; display: inline-block !important; position: absolute !important; width: 1px !important; right: 0px !important; outline: 0px !important; background: 0px 0px !important; text-decoration: initial !important; text-shadow: initial !important; }
.md-inline-math .MathJax_SVG .noError { display: none !important; }
.html-for-mac .inline-math-svg .MathJax_SVG { vertical-align: 0.2px; }
.md-math-block .MathJax_SVG_Display { text-align: center; margin: 0px; position: relative; text-indent: 0px; max-width: none; max-height: none; min-height: 0px; min-width: 100%; width: auto; overflow-y: hidden; display: block !important; }
.MathJax_SVG_Display, .md-inline-math .MathJax_SVG_Display { width: auto; margin: inherit; display: inline-block !important; }
.MathJax_SVG .MJX-monospace { font-family: var(--monospace); }
.MathJax_SVG .MJX-sans-serif { font-family: sans-serif; }
.MathJax_SVG { display: inline; font-style: normal; font-weight: 400; line-height: normal; zoom: 90%; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; }
.MathJax_SVG * { transition: none; }
.MathJax_SVG_Display svg { vertical-align: middle !important; margin-bottom: 0px !important; }
.os-windows.monocolor-emoji .md-emoji { font-family: "Segoe UI Symbol", sans-serif; }
.md-diagram-panel > svg { max-width: 100%; }
[lang="mermaid"] svg, [lang="flow"] svg { max-width: 100%; }
[lang="mermaid"] .node text { font-size: 1rem; }
table tr th { border-bottom: 0px; }
video { max-width: 100%; display: block; margin: 0px auto; }
iframe { max-width: 100%; width: 100%; border: none; }
.highlight td, .highlight tr { border: 0px; }

.CodeMirror { height: auto; }
.CodeMirror.cm-s-inner { background: inherit; }
.CodeMirror-scroll { overflow-y: hidden; overflow-x: auto; z-index: 3; }
.CodeMirror-gutter-filler, .CodeMirror-scrollbar-filler { background-color: rgb(255, 255, 255); }
.CodeMirror-gutters { border-right: 1px solid rgb(221, 221, 221); background: inherit; white-space: nowrap; }
.CodeMirror-linenumber { padding: 0px 3px 0px 5px; text-align: right; color: rgb(153, 153, 153); }
.cm-s-inner .cm-keyword { color: rgb(119, 0, 136); }
.cm-s-inner .cm-atom, .cm-s-inner.cm-atom { color: rgb(34, 17, 153); }
.cm-s-inner .cm-number { color: rgb(17, 102, 68); }
.cm-s-inner .cm-def { color: rgb(0, 0, 255); }
.cm-s-inner .cm-variable { color: rgb(0, 0, 0); }
.cm-s-inner .cm-variable-2 { color: rgb(0, 85, 170); }
.cm-s-inner .cm-variable-3 { color: rgb(0, 136, 85); }
.cm-s-inner .cm-string { color: rgb(170, 17, 17); }
.cm-s-inner .cm-property { color: rgb(0, 0, 0); }
.cm-s-inner .cm-operator { color: rgb(152, 26, 26); }
.cm-s-inner .cm-comment, .cm-s-inner.cm-comment { color: rgb(170, 85, 0); }
.cm-s-inner .cm-string-2 { color: rgb(255, 85, 0); }
.cm-s-inner .cm-meta { color: rgb(85, 85, 85); }
.cm-s-inner .cm-qualifier { color: rgb(85, 85, 85); }
.cm-s-inner .cm-builtin { color: rgb(51, 0, 170); }
.cm-s-inner .cm-bracket { color: rgb(153, 153, 119); }
.cm-s-inner .cm-tag { color: rgb(17, 119, 0); }
.cm-s-inner .cm-attribute { color: rgb(0, 0, 204); }
.cm-s-inner .cm-header, .cm-s-inner.cm-header { color: rgb(0, 0, 255); }
.cm-s-inner .cm-quote, .cm-s-inner.cm-quote { color: rgb(0, 153, 0); }
.cm-s-inner .cm-hr, .cm-s-inner.cm-hr { color: rgb(153, 153, 153); }
.cm-s-inner .cm-link, .cm-s-inner.cm-link { color: rgb(0, 0, 204); }
.cm-negative { color: rgb(221, 68, 68); }
.cm-positive { color: rgb(34, 153, 34); }
.cm-header, .cm-strong { font-weight: 700; }
.cm-del { text-decoration: line-through; }
.cm-em { font-style: italic; }
.cm-link { text-decoration: underline; }
.cm-error { color: red; }
.cm-invalidchar { color: red; }
.cm-constant { color: rgb(38, 139, 210); }
.cm-defined { color: rgb(181, 137, 0); }
div.CodeMirror span.CodeMirror-matchingbracket { color: rgb(0, 255, 0); }
div.CodeMirror span.CodeMirror-nonmatchingbracket { color: rgb(255, 34, 34); }
.cm-s-inner .CodeMirror-activeline-background { background: inherit; }
.CodeMirror { position: relative; overflow: hidden; }
.CodeMirror-scroll { height: 100%; outline: 0px; position: relative; box-sizing: content-box; background: inherit; }
.CodeMirror-sizer { position: relative; }
.CodeMirror-gutter-filler, .CodeMirror-hscrollbar, .CodeMirror-scrollbar-filler, .CodeMirror-vscrollbar { position: absolute; z-index: 6; display: none; }
.CodeMirror-vscrollbar { right: 0px; top: 0px; overflow: hidden; }
.CodeMirror-hscrollbar { bottom: 0px; left: 0px; overflow: hidden; }
.CodeMirror-scrollbar-filler { right: 0px; bottom: 0px; }
.CodeMirror-gutter-filler { left: 0px; bottom: 0px; }
.CodeMirror-gutters { position: absolute; left: 0px; top: 0px; padding-bottom: 30px; z-index: 3; }
.CodeMirror-gutter { white-space: normal; height: 100%; box-sizing: content-box; padding-bottom: 30px; margin-bottom: -32px; display: inline-block; }
.CodeMirror-gutter-wrapper { position: absolute; z-index: 4; background: 0px 0px !important; border: none !important; }
.CodeMirror-gutter-background { position: absolute; top: 0px; bottom: 0px; z-index: 4; }
.CodeMirror-gutter-elt { position: absolute; cursor: default; z-index: 4; }
.CodeMirror-lines { cursor: text; }
.CodeMirror pre { border-radius: 0px; border-width: 0px; background: 0px 0px; font-family: inherit; font-size: inherit; margin: 0px; white-space: pre; word-wrap: normal; color: inherit; z-index: 2; position: relative; overflow: visible; }
.CodeMirror-wrap pre { word-wrap: break-word; white-space: pre-wrap; word-break: normal; }
.CodeMirror-code pre { border-right: 30px solid transparent; width: fit-content; }
.CodeMirror-wrap .CodeMirror-code pre { border-right: none; width: auto; }
.CodeMirror-linebackground { position: absolute; left: 0px; right: 0px; top: 0px; bottom: 0px; z-index: 0; }
.CodeMirror-linewidget { position: relative; z-index: 2; overflow: auto; }
.CodeMirror-wrap .CodeMirror-scroll { overflow-x: hidden; }
.CodeMirror-measure { position: absolute; width: 100%; height: 0px; overflow: hidden; visibility: hidden; }
.CodeMirror-measure pre { position: static; }
.CodeMirror div.CodeMirror-cursor { position: absolute; visibility: hidden; border-right: none; width: 0px; }
.CodeMirror div.CodeMirror-cursor { visibility: hidden; }
.CodeMirror-focused div.CodeMirror-cursor { visibility: inherit; }
.cm-searching { background: rgba(255, 255, 0, 0.4); }
@media print {
.CodeMirror div.CodeMirror-cursor { visibility: hidden; }
}

:root { --side-bar-bg-color: #fafafa; --control-text-color: #777; }
html { font-size: 16px; }
body { font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif; color: rgb(51, 51, 51); line-height: 1.6; }
#write { max-width: 860px; margin: 0px auto; padding: 30px 30px 100px; }
#write > ul:first-child, #write > ol:first-child { margin-top: 30px; }
a { color: rgb(65, 131, 196); }
h1, h2, h3, h4, h5, h6 { position: relative; margin-top: 1rem; margin-bottom: 1rem; font-weight: bold; line-height: 1.4; cursor: text; }
h1:hover a.anchor, h2:hover a.anchor, h3:hover a.anchor, h4:hover a.anchor, h5:hover a.anchor, h6:hover a.anchor { text-decoration: none; }
h1 tt, h1 code { font-size: inherit; }
h2 tt, h2 code { font-size: inherit; }
h3 tt, h3 code { font-size: inherit; }
h4 tt, h4 code { font-size: inherit; }
h5 tt, h5 code { font-size: inherit; }
h6 tt, h6 code { font-size: inherit; }
h1 { padding-bottom: 0.3em; font-size: 2.25em; line-height: 1.2; border-bottom: 1px solid rgb(238, 238, 238); }
h2 { padding-bottom: 0.3em; font-size: 1.75em; line-height: 1.225; border-bottom: 1px solid rgb(238, 238, 238); }
h3 { font-size: 1.5em; line-height: 1.43; }
h4 { font-size: 1.25em; }
h5 { font-size: 1em; }
h6 { font-size: 1em; color: rgb(119, 119, 119); }
p, blockquote, ul, ol, dl, table { margin: 0.8em 0px; }
li > ol, li > ul { margin: 0px; }
hr { height: 2px; padding: 0px; margin: 16px 0px; background-color: rgb(231, 231, 231); border: 0px none; overflow: hidden; box-sizing: content-box; }
li p.first { display: inline-block; }
ul, ol { padding-left: 30px; }
ul:first-child, ol:first-child { margin-top: 0px; }
ul:last-child, ol:last-child { margin-bottom: 0px; }
blockquote { border-left: 4px solid rgb(223, 226, 229); padding: 0px 15px; color: rgb(119, 119, 119); }
blockquote blockquote { padding-right: 0px; }
table { padding: 0px; word-break: initial; }
table tr { border-top: 1px solid rgb(223, 226, 229); margin: 0px; padding: 0px; }
table tr:nth-child(2n), thead { background-color: rgb(248, 248, 248); }
table tr th { font-weight: bold; border-width: 1px 1px 0px; border-top-style: solid; border-right-style: solid; border-left-style: solid; border-top-color: rgb(223, 226, 229); border-right-color: rgb(223, 226, 229); border-left-color: rgb(223, 226, 229); border-image: initial; border-bottom-style: initial; border-bottom-color: initial; text-align: left; margin: 0px; padding: 6px 13px; }
table tr td { border: 1px solid rgb(223, 226, 229); text-align: left; margin: 0px; padding: 6px 13px; }
table tr th:first-child, table tr td:first-child { margin-top: 0px; }
table tr th:last-child, table tr td:last-child { margin-bottom: 0px; }
.CodeMirror-lines { padding-left: 4px; }
.code-tooltip { box-shadow: rgba(0, 28, 36, 0.3) 0px 1px 1px 0px; border-top: 1px solid rgb(238, 242, 242); }
.md-fences, code, tt { border: 1px solid rgb(231, 234, 237); background-color: rgb(248, 248, 248); border-radius: 3px; padding: 2px 4px 0px; font-size: 0.9em; }
code { background-color: rgb(243, 244, 244); padding: 0px 2px; }
.md-fences { margin-bottom: 15px; margin-top: 15px; padding-top: 8px; padding-bottom: 6px; }
.md-task-list-item > input { margin-left: -1.3em; }
@media print {
html { font-size: 13px; }
table, pre { break-inside: avoid; }
pre { word-wrap: break-word; }
}
.md-fences { background-color: rgb(248, 248, 248); }
#write pre.md-meta-block { padding: 1rem; font-size: 85%; line-height: 1.45; background-color: rgb(247, 247, 247); border: 0px; border-radius: 3px; color: rgb(119, 119, 119); margin-top: 0px !important; }
.mathjax-block > .code-tooltip { bottom: 0.375rem; }
.md-mathjax-midline { background: rgb(250, 250, 250); }
#write > h3.md-focus::before { left: -1.5625rem; top: 0.375rem; }
#write > h4.md-focus::before { left: -1.5625rem; top: 0.285714rem; }
#write > h5.md-focus::before { left: -1.5625rem; top: 0.285714rem; }
#write > h6.md-focus::before { left: -1.5625rem; top: 0.285714rem; }
.md-image > .md-meta { border-radius: 3px; padding: 2px 0px 0px 4px; font-size: 0.9em; color: inherit; }
.md-tag { color: rgb(167, 167, 167); opacity: 1; }
.md-toc { margin-top: 20px; padding-bottom: 20px; }
.sidebar-tabs { border-bottom: none; }
#typora-quick-open { border: 1px solid rgb(221, 221, 221); background-color: rgb(248, 248, 248); }
#typora-quick-open-item { background-color: rgb(250, 250, 250); border-color: rgb(254, 254, 254) rgb(229, 229, 229) rgb(229, 229, 229) rgb(238, 238, 238); border-style: solid; border-width: 1px; }
.on-focus-mode blockquote { border-left-color: rgba(85, 85, 85, 0.12); }
header, .context-menu, .megamenu-content, footer { font-family: "Segoe UI", Arial, sans-serif; }
.file-node-content:hover .file-node-icon, .file-node-content:hover .file-node-open-state { visibility: visible; }
.mac-seamless-mode #typora-sidebar { background-color: var(--side-bar-bg-color); }
.md-lang { color: rgb(180, 101, 77); }
.html-for-mac .context-menu { --item-hover-bg-color: #E6F0FE; }
#md-notification .btn { border: 0px; }
.dropdown-menu .divider { border-color: rgb(229, 229, 229); }

.typora-export li, .typora-export p, .typora-export, .footnote-line {white-space: normal;}
-->

Web-动态页面

1. JSP:

1. 指令

2. 注释

3. 内置对象

2. MVC开发模式

3. EL表达式

4. JSTL标签

5. 三层架构

JSP:

1. 指令

* 作用：用于配置JSP页面，导入资源文件

* 格式：

<%@ 指令名称 属性名1=属性值1 属性名2=属性值2 ... %>

* 分类：

1. page： 配置JSP页面的

* contentType：等同于response.setContentType()

1. 设置响应体的mime类型以及字符集

2. 设置当前jsp页面的编码（只能是高级的IDE才能生效，如果使用低级工具，则需要设置pageEncoding属性设置当前页面的字符集）

* import：导包

* errorPage：当前页面发生异常后，会自动跳转到指定的错误页面

* isErrorPage：标识当前也是是否是错误页面。

* true：是，可以使用内置对象exception

* false：否。默认值。不可以使用内置对象exception

2. include： 页面包含的。导入页面的资源文件

* <%@include file="top.jsp"%>

3. taglib： 导入资源

* <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

* prefix：前缀，自定义的

2. 注释:

1. html注释：

<!-- -->:只能注释html代码片段

2. jsp注释：推荐使用

<%-- --%>：可以注释所有

3. 内置对象

* 在jsp页面中不需要创建，直接使用的对象

* 一共有9个：

变量名真实类型作用

* pageContextPageContext当前页面共享数据，还可以获取其他八个内置对象

* requestHttpServletRequest一次请求访问的多个资源(转发)

* sessionHttpSession一次会话的多个请求间

* applicationServletContext所有用户间共享数据

* responseHttpServletResponse响应对象

* pageObject当前页面(Servlet)的对象  this

* outJspWriter输出对象，数据输出到页面上

* configServletConfigServlet的配置对象

* exceptionThrowable异常对象

MVC：开发模式

xxxxxxxxxx

1. jsp演变历史

1. 早期只有servlet，只能使用response输出标签数据，非常麻烦

2. 后来又jsp，简化了Servlet的开发，如果过度使用jsp，在jsp中即写大量的java代码，有写html表，造成难于维护，难于分工协作

3. 再后来，java的web开发，借鉴mvc开发模式，使得程序的设计更加合理性

2. MVC：

1. M：Model，模型。JavaBean

* 完成具体的业务操作，如：查询数据库，封装对象

2. V：View，视图。JSP

* 展示数据

3. C：Controller，控制器。Servlet

* 获取用户的输入

* 调用模型

* 将数据交给视图进行展示

* 优缺点：

1. 优点：

1. 耦合性低，方便维护，可以利于分工协作

2. 重用性高

2. 缺点：

1. 使得项目架构变得复杂，对开发人员要求高

EL表达式

1. 概念：Expression Language 表达式语言

2. 作用：替换和简化jsp页面中java代码的编写

3. 语法：${表达式}

4. 注意：

* jsp默认支持el表达式的。如果要忽略el表达式

1. 设置jsp中page指令中：isELIgnored="true" 忽略当前jsp页面中所有的el表达式

2. \${表达式} ：忽略当前这个el表达式

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5. 使用：

1. 运算：

* 运算符：

1. 算数运算符： + - * /(div) %(mod)

2. 比较运算符： > < >= <= == !=

3. 逻辑运算符： &&(and) ||(or) !(not)

4. 空运算符： empty

* 功能：用于判断字符串、集合、数组对象是否为null或者长度是否为0

* ${empty list}:判断字符串、集合、数组对象是否为null或者长度为0

* ${not empty str}:表示判断字符串、集合、数组对象是否不为null 并且 长度>0

2. 获取值

1. el表达式只能从域对象中获取值

2. 语法：

1. ${域名称.键名}：从指定域中获取指定键的值

* 域名称：

1. pageScope--> pageContext

2. requestScope --> request

3. sessionScope --> session

4. applicationScope --> application（ServletContext）

* 举例：在request域中存储了name=张三

* 获取：${requestScope.name}

2. ${键名}：表示依次从最小的域中查找是否有该键对应的值，直到找到为止。

获取对象、List集合、Map集合的值
1. 对象：${域名称.键名.属性名}
  - 本质上会去调用对象的getter方法

2. List集合：${域名称.键名[索引]}

3. Map集合：

* ${域名称.键名.key名称}

* ${域名称.键名["key名称"]}

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3. 隐式对象：

* pageContext：

* 获取jsp其他八个内置对象

* ${pageContext.request.contextPath}：动态获取虚拟目录

JSTL

1. 概念：JavaServer Pages Tag Library  JSP标准标签库

* 是由Apache组织提供的开源的免费的jsp标签<标签>

2. 作用：用于简化和替换jsp页面上的java代码

3. 使用步骤：

1. 导入jstl相关jar包

2. 引入标签库：taglib指令：  <%@ taglib %>

3. 使用标签

4. 常用的JSTL标签

1. if:相当于java代码的if语句

1. 属性：

            * test 必须属性，接受boolean表达式

                * 如果表达式为true，则显示if标签体内容，如果为false，则不显示标签体内容

                * 一般情况下，test属性值会结合el表达式一起使用

    2. 注意：

        * c:if标签没有else情况，想要else情况，则可以在定义一个c:if标签

2. choose:相当于java代码的switch语句

1. 使用choose标签声明         相当于switch声明

        2. 使用when标签做判断         相当于case

        3. 使用otherwise标签做其他情况的声明    相当于default

3. foreach:相当于java代码的for语句

5. 练习：

* 需求：在request域中有一个存有User对象的List集合。需要使用jstl+el将list集合数据展示到jsp页面的表格table中

三层架构：软件设计架构

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1. 界面层(表示层)：用户看的得界面。用户可以通过界面上的组件和服务器进行交互

2. 业务逻辑层：处理业务逻辑的。

3. 数据访问层：操作数据存储文件。

巴特西

Web-动态页面

Web-动态页面

JSP:

MVC：开发模式

EL表达式

JSTL

三层架构：软件设计架构

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