JSP CHEAT SHEETS

Default Scripting Language

The scripting language of a JSP page defaults to Java.

To configure the page to use JavaScript:

<%@ page language = "javascript" %>

Using White Space

White space contained within the template code is returned to the client as it was entered in the JSP.

Quoting Attribute Values

Quote attribute values using either single or double quotes for JSP elements.

<%@ page contentType = "text/plain" %>

Writing Comments for the JSP

A JSP comment is not output to the client as part of the JSP page's output.

<%-- Comment string... --%>

Outputting Comments to the Client

HTML comments are output to the client.

<!-- comments -->

<%@ page attribute="value" ... %>

<%@ include file = "path" ... %>

<%@ taglib uri="tagLibraryURI"
prefix="tagPrefix" %>

Page Directive Attributes

The value is a string literal in single or double quotes.

<%! declaration %>

<% script code %>

<%= expression %>

Declaration Example

<%!
private String foo = null;
public String getFoo() {
    return this.foo;
}
%>

Scriptlet Example

<%
String greeting = request.getParameter("Greeting");
out.println(greeting);
%>

Expression Example

<%= myVar1 %>

jsp:include

Calls one JSP page from another. Upon completion, the destination page returns control to the calling page.

<jsp:include page="path" flush="true"/>

<jsp:include page="path" flush="true">
    <jsp:param name="paramName"
               value="paramValue" />
</jsp:include>

jsp:forward

Calls one JSP page from another. Execution of the calling page is terminated by the call.

<jsp:forward page="path" />

<jsp:forward page="path">
    <jsp:param name="paramName"
               value="paramValue" />
</jsp:forward>

jsp:plugin

Enables you to invoke an applet on a client browser.

<jsp:plugin
    type="bean|applet"
    code="objectCode"
    codebase="objectCodebase"
    align="alignment"
    archive="archiveList"
    height="height"
    hspace="hspace"
    jreversion="jreversion"
    name="componentName"
    vspace="vspace"
    width="width"
    nspluginurl="url"
    iepluginurl="url">

    <jsp:params>
        <jsp:param name="paramName"
                   value="paramValue" />
    </jsp:params>

    <jsp:fallback>
        arbitrary_text
    </jsp:fallback>

</jsp:plugin>

jsp:useBean

Defines an instance of a Java bean.

<jsp:useBean id="name"
    scope="page|request|session|application"
    typeSpec />

<jsp:useBean id="name"
    scope="page|request|session|application"
    typeSpec>
    body
</jsp:useBean>

typespec:

• class="className"
• class="className" type="typeName"
• beanName="beanName" type="typeName"
• type="typeName"

jsp:setProperty

Sets the value of one or more properties in a bean.

<jsp:setProperty name="beanName" prop_expr />

prop_expr can be:

• property="*"
• property="propertyName"
• property="propertyName" param="parameterName"
• property="propertyName" value="propertyValue"

jsp:getProperty

Writes the value of a bean property as a string to the out object.

<jsp:getProperty name="name"
    property="propertyName" />

J2EE Structure

JSP Fundamentals

JSP Built-in Objects

<form id="test"
      action="student-response.jsp"
      method="post">

    name:
    <input type="text" name="name"/>

    <input type="radio"
           name="isSophomore"
           value="Yes"> Yes

    <input type="radio"
           name="isSophomore"
           value="No"> No

    <input type="checkbox"
           name="language"
           value="Javascript"> Javascript

    <input type="checkbox"
           name="language"
           value="Java"> Java

    <input type="checkbox"
           name="language"
           value="SQL"> SQL

    <input type="checkbox"
           name="language"
           value="python"> Python

    <input type="submit" value="Submit"/>
</form>

<select name="country" form="test">
    <option value="China">China</option>
    <option value="US">US</option>
    <option value="Other">Other</option>
</select>

Reading Form Parameters in JSP

${param.name}
${param.country}

<%=request.getParameter("country")%>

Reading Multiple Checkbox Values

<ul>
<%
String[] language =
    request.getParameterValues("language");

if (language != null)
    for (String s : language)
        out.println("<li>" + s + "</li>");
%>
</ul>

A session is unique for a user and can share data across pages, such as a shopping cart for a user. It is kept in memory and each user has a session ID. The browser handles the session ID.

Typical flow:

1. Create form
2. Check and set session attribute
3. Read from session

To disable session:

<%@ page session="false" %>

PageContext

The reference also lists PageContext in the session section.

Cookie API

Cookie API is in javax.servlet.http and is imported implicitly for JSP pages.

Cookie(String name, String value);

Cookie theCookie =
    new Cookie("myApp.favoriteLang", favLang);

theCookie.setMaxAge(606024*365);

// default 30min
response.addCookie(theCookie);

Cookie[] theCookies = request.getCookies();

if (theCookies != null) {
    for (Cookie tempCookie : theCookies) {
        // process cookie
    }
}

Cookie Characteristics

• Only sent to the specific server when the domain matches.
• A cookie is data stored by the browser and sent to the server with every request.
• Cookies with no expiration time can be deleted after the browser is closed, depending on browser behavior.

Cookie vs Session

Reading Cookies

<%
Cookie[] theCookies = request.getCookies();

if (theCookies != null) {
    for (Cookie tempCookie : theCookies) {

        if ("myApp.favoriteLang"
                .equals(tempCookie.getName())) {

            favLang = tempCookie.getValue();
            break;
        }
    }
}
%>

Setup Notes from the Reference

• Install MySQL, Workbench, Shell and demo data setup.
• Set up Tomcat 7.0 by downloading Tomcat 7 and unzipping it to c:\.
• Set up a connection pool for multiple users sharing the same database.
• The pool saves resources by avoiding a new connection setup every time.
• Download the MySQL JDBC connector JAR and place it under WebContent/WEB-INF/lib.
• Define the connection pool in WebContent/META-INF/context.xml.

Tomcat DataSource Configuration

<Context>

    <Resource
        name="jdbc/web_student_tracker"
        auth="Container"
        type="javax.sql.DataSource"
        maxActive="20"
        maxIdle="5"
        maxWait="10000"
        username="webstudent"
        password="webstudent"
        driverClassName="com.mysql.jdbc.Driver"
        url="jdbc:mysql://localhost:3306/web_student_tracker?useSSL=false"
    />

</Context>

Resource Injection

Tomcat automatically sets the connection pool / datasource on the servlet, according to the supplied reference.

Connector / MySQL Note

-- connector/J 8

alter user 'webstudent'@'localhost'
identified with mysql_native_password
by 'webstudent';

Cache Busting

The second supplied cheat sheet contains a cache-busting reference.

https://curtistimson.co.uk/post/front-end-dev/what-is-cache-busting/