jsp

1. comment
<!-- -->
/* */  java comment
<%-- --%>  JSP comment

2. scriptlet
1)  <% %>: code
2)  <%! %>: global variables, functions, classes. CANNOT write any statements
		<%!
		public static final String DBDRIVER = "oracle.jdbc.driver.OracleDriver" ;
		public static final String DBURL = "jdbc:oracle:thin:@localhost:1521:MLDN" ;
		%>
		<%
			out.print("<h1>DBDRRIVER = " + DBDRIVER + "</h1>") ;
			out.print("<h1>DBURL = " + DBURL + "</h1>") ;
		%>
3)  <%= %>: variables

	<%
		out.println("<table>") ;
		for(int i=0;i<100;i++){
			out.println("<tr>") ;
			for(int j=0;j<100;j++){
				out.print("<td>" + (i * j) + "</td>") ;
			}
			out.println("</tr>") ;
		}
		out.println("</table>") ;
	%>


3. Page instruction

1) set MIME
    <%@page contentType="text/html;charset=GBK"%>

    conf/web.xml
    <mime-mapping>
        <extension>htm</extension>
        <mime-type>text/html</mime-type>
    </mime-mapping>
    
    <mime-mapping>
        <extension>doc</extension>
        <mime-type>application/msword</mime-type>
    </mime-mapping>
    
2) import instruction
    <%@page import="java.sql.*"%>
    
    jar file: in tomcat/common/lib
    
    
    example:
        <%!
            public static final String DBDRIVER = "...";
            public static final String DBURL = "...";
            ...
        %>
        <%
            Connection conn = null;
            PreparedStatement pstmt = null;
            ResultSet rs = null;
        %>
        
4. include instruction
1) static include: include the content only, text include
    <%@include file="content.htm" %>

2) dynamic include    
    <jsp:include page="content.jsp">
        <jsp:param name="ref1" value="HELLO WORLD"/>
    </jsp:include>
    
5. forward instruction
<jsp:forward page="demo.jsp" />
    browser address will not change. It is server forward.
    
    
6. Servlet
    Servlet put in WEB-INF/classes
    
    Import requirement:
        java package: java.util.*
        java subpackage: java.lang.reflect;
        java extension: javax.*;
        java extension subpackage: javax.servlet.*;
        custom package;
       
    1) RESPONSE 
        
        PrintWriter out = resp.getWriter();
        out.println("<h1><font color=\"red\">Hello World</font></h1>");
        out.close();
        
        Under J2SE environment, javax.servlet etc. need to be imported.
        
        
        IMPORTING PACKAGES:
            Tomcat procedure: jsp -> java -> class
            In Tomcat, \common\lib has a servlet-api.jar, many classes are inside.
            Set CLASSPATH, to this jar, then j2se java will check this jar as a library.
            In Windows, we can copy this jar to jdk ext, so that we don't need to import this jar every time we use it.
            
            jre\lib\ext\: store all extension jars
            This is a unsafe folder.
            
            in jre\lib\security\java.policy, there is 
                "grant codeBase "file:..."
                
            WEB-INF is the most safe folder in web container, 
            
        CONFIG SERVLET
            <servlet>
                <servlet-name>hello</servlet-name>
                <servlet-class>org.allen.HelloServlet</servlet-class>
            </servlet>
            <servlet-mapping>
                <servlet-name>hello</servlet-name>
                <url-pattern>/demo</url-pattern>
            </servlet-mapping>
            
            ex.
                /demo
                HelloServlet called.
    
    2) REQUEST
        String param = req.getParameter("param");
        
        <ex1>
            web.xml: 
                servlet-name: input
                url-pattern: /input (this is under root directory)
            the form that post to /input is /serdemo/index.htm 
                <form action="input" method="post">
                
        *ClassNotFoundException: recompile servlet class
        servlet 路径是表单和url拼凑出来的
        建议在web.xml中url-pattern中填写完整路径
        
        doPost(req, resp)
        {
            this.doGet(req, resp);
        }
            
        
    3) LifeCycle
        HttpServlet
            - init()
            - init(ServletConfig conf)
                conf.getInitParameter();
                
                    in web.xml, <init-param> <param-name></>  <param-value></> </>
            - service()
                if service() is override, then doPost(), doGet() will not be run, because they all in a abstract service() in its father class.
                Container -> service() -> doXXX()
            - destroy()
        
        in web.xml, if a servlet is declared <load-on-startup>1</> then it will start on server start up.
        
    4) get other global object
        HttpSession getSession()
        
    5) redirect
            CLIENT REDIRECT
                resp.sendRedirect() is a client redirect. Address in browser will change.
                If pass attribute to redirect, use Session object is the best way
                
                req.getSession().setAttribute("name", "Hello world");
                
                If attribute used only one time, use request
            
            SERVER REDIRECT( frequently used)
                RequestDispatcher 
                    
                    req.setAttribute("name", "hello world");
                    RequestDispatcher rd = req.getRequestDispatcher("demo.jsp");
                    rd.forward(req, resp);