jsp是在html中嵌入java代码
jsp也是在j2ee服务端中的java组件
第一次运行
在第一次运行jsp代码时会经历以下步骤，将jsp转为java代码，将java代码转为class文件。
所以通常会比较慢，编译后就好多了。
四大作用域
- request
- session
- page
- application
部署jsp
<servlet>
<servlet-name>a<servlet-name/>
<jsp-file>/a.jsp<jsp-file/>
<servlet-mappiing>
<servlet-name><servlet-name/>
<url-pattern><url-pattern/>
<servlet-mappiing/>
<servlet/>
jsp作为servlet的继承者，自然是可以部署的，但是一般不会这么做。
内嵌java语法
<%@ %>jsp指令的语法<%= %>jsp表达式的语法<%! %>jsp声明的语法<%-- --%>jsp注释的语法<% %>jsp中可以放置任何合法的java代码，其最终会被转换到service代码内。
jsp指令
<%@ page 属性列表%>定义页面的依赖属性，如脚本语言，error页面，缓存需求等<%@ include file="afile" %>包含其它文件<%@ taglib uri="" prefix="a" %>标签库的定义
例子
<%@ page import="java.util.*,java.net.*,java.io.*" session="true" isErrorPage="false" errorPage="/error.jsp"%>
<%@ include file="copyright.html" %>
Jsp声明
声明函数或变量，供后续使用。
<%! int i = 0;%>
<%! Circle a = new Circle(2.0);%>
或者
<jsp:declaration>
int i = 0;
<jsp:declaration/>
Jsp的action行为标签
9个隐式变量（内置变量）
HttpServletRequest request
HttpServletEesponse response
ServletContext application
PageContext pagecontext
ServletConfig config
HttpSession session
JspWriter out
Exception exception
page,等价于this
考试重点JspWriter，PageContext
package javax.servlet.jsp
public abstract class JspWriter extends Writer {
public static final int NO_BUFFER = 0;
public static final int DEFAULT_BUFFER = -1;指示 Writer 已缓冲并使用实现默认缓冲区大小的常量。
public static final int UNBOUNDED_BUFFER = -2;常量表示 Writer 是缓冲的并且是无界的;这在 BodyContent 中使用。
protected int bufferSize;
protected boolean autoFlush;
protected JspWriter(int bufferSize, boolean autoFlush) {
this.bufferSize = bufferSize;
this.autoFlush = autoFlush;
}
public abstract void newLine() throws IOException;
public abstract void print(boolean var1) throws IOException;
public abstract void print(char var1) throws IOException;
public abstract void print(int var1) throws IOException;
public abstract void print(long var1) throws IOException;
public abstract void print(float var1) throws IOException;
public abstract void print(double var1) throws IOException;
public abstract void print(char[] var1) throws IOException;
public abstract void print(String var1) throws IOException;
public abstract void print(Object var1) throws IOException;
public abstract void println() throws IOException;
public abstract void println(boolean var1) throws IOException;
public abstract void println(char var1) throws IOException;
public abstract void println(int var1) throws IOException;
public abstract void println(long var1) throws IOException;
public abstract void println(float var1) throws IOException;
public abstract void println(double var1) throws IOException;
public abstract void println(char[] var1) throws IOException;
public abstract void println(String var1) throws IOException;
public abstract void println(Object var1) throws IOException;
public abstract void clear() throws IOException;
public abstract void clearBuffer() throws IOException;
public abstract void flush() throws IOException;
public abstract void close() throws IOException;
public int getBufferSize() {
return this.bufferSize;
}
public abstract int getRemaining();此方法返回缓冲区中未使用的字节数。
public boolean isAutoFlush() {
return this.autoFlush;
}
}
package javax.servlet.jsp
public abstract class PageContext extends JspContext {
public static final int PAGE_SCOPE = 1;
public static final int REQUEST_SCOPE = 2;
public static final int SESSION_SCOPE = 3;
public static final int APPLICATION_SCOPE = 4;
public static final String PAGE = "javax.servlet.jsp.jspPage";
public static final String PAGECONTEXT = "javax.servlet.jsp.jspPageContext";
public static final String REQUEST = "javax.servlet.jsp.jspRequest";
public static final String RESPONSE = "javax.servlet.jsp.jspResponse";
public static final String CONFIG = "javax.servlet.jsp.jspConfig";
public static final String SESSION = "javax.servlet.jsp.jspSession";
public static final String OUT = "javax.servlet.jsp.jspOut";
public static final String APPLICATION = "javax.servlet.jsp.jspApplication";
public static final String EXCEPTION = "javax.servlet.jsp.jspException";
public PageContext() {
}
public abstract void initialize(Servlet var1, ServletRequest var2, ServletResponse var3, String var4, boolean var5, int var6, boolean var7) throws IOException, IllegalStateException, IllegalArgumentException;
public abstract void release();
public abstract HttpSession getSession();
public abstract Object getPage();页面对象的当前值（在 Servlet 环境中，这是 javax.servlet.Servlet 的实例）。
public abstract ServletRequest getRequest();请求对象 （ServletRequest） 的当前值。
public abstract ServletResponse getResponse();响应对象 （ServletResponse） 的当前值。
public abstract Exception getException();
public abstract ServletConfig getServletConfig();
public abstract ServletContext getServletContext();
public abstract void forward(String var1) throws ServletException, IOException;
public abstract void include(String var1) throws ServletException, IOException;
public abstract void include(String var1, boolean var2) throws ServletException, IOException;
public abstract void handlePageException(Exception var1) throws ServletException, IOException;
public abstract void handlePageException(Throwable var1) throws ServletException, IOException;
public BodyContent pushBody() {
return null;
}
public ErrorData getErrorData() {
return new ErrorData((Throwable)this.getRequest().getAttribute("javax.servlet.error.exception"), (Integer)this.getRequest().getAttribute("javax.servlet.error.status_code"), (String)this.getRequest().getAttribute("javax.servlet.error.request_uri"), (String)this.getRequest().getAttribute("javax.servlet.error.servlet_name"));
}
}
JSP EL表达式
<%
request.setAttribute("a","hello")
%>
${a}
会在四大作用域中依次搜索a这个键名。
显示hello
变量定义使用setAttribute()方法进行设置，可以设置在四大作用域中的任意一个域中。
预定义11个对象
为了方便使用，定义了可以直接供我们使用的11个对象。
大多是都是用Map存储，采用键值对的形式。
- pageContext
- param
- paramValues
- header
- headerValues
- cookie
- initParam
- pageScope
- requestScope
- sessionScope
- applicationScope
只有pageContext是PageContext类型。
