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| - | In this part of the JEE tutorials, we will talk about client side Java Beans components. This is a technology directly supported by the JavaServer pages.
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| - | Java Beans are reusable software components. The idea behind a software component is to create a specialized piece of self-contained code, that could be easily plugged into various applications as needed. For example in GUI programming, we might have a chart, a clock or a spreadsheet component that could be used in an application without exposing the programmer to complicated details that are behind the code.
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| - | Technically Java Beans are Java classes conforming to particular conventions. A bean can be a particular specialized Java Swing component (e.g. a chart ) that can be plugged into the application, a server side component called <b>Enterprise Java Bean</b>, EJB or a client side component. In this chapter, we will talk about client side Java Beans.
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| - | * The class must have a no-argument public constructor
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| - | * The properties of the Bean must be accessible using accessor methods
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| - | * The class should be serializable
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| - | JavaServer Pages technology directly supports using JavaBeans components with standard JSP language elements.
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| - | == A Bean ==
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| - | In the Bean example we have a form that sends data to a jsp page. The jsp page will output those data.
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| - | This time we do not use scriptlets or expressions, but we use Java Beans technology.
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| - | <source lang="java">
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| - | * { font-size: 12px; font-family: Verdana }
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| - | input { border: 1px solid #ccc }
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| - | </source>
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| - | This is a css file for the code example.
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| - | <source lang="java">
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| - | <%@page contentType="text/html" pageEncoding="UTF-8"%>
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| - | <html>
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| - | <head>
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| - | <title>Bean</title>
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| - | <link rel="stylesheet" href="style.css" type="text/css">
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| - | </head>
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| - | <body>
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| - | <form action="show.jsp" method="post">
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| - | <table>
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| - | <tr>
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| - | <td>Author</td>
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| - | <td><input type="text" name="author"></td>
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| - | </tr>
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| - | <tr>
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| - | <td>Title</td>
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| - | <td><input type="text" name="title"></td>
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| - | </tr>
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| - | <tr>
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| - | <td>Available</td>
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| - | <td><input type="checkbox" name="available" value="true"></td>
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| - | </tr>
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| - | </table>
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| - | <br>
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| - | <input type="submit" value="submit">
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| - | </form>
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| - | </body>
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| - | </html>
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| - | </source>
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| - | Here we define a simple form. We have three input boxes. The author, title and the availability of the book.
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| - | The parameters are sent to the show.jsp page.
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| - | <source lang="java">
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| - | package com.zetcode;
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| - | import java.io.Serializable;
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| - | public class MyBean implements Serializable {
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| - | private String author = "";
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| - | private String title = "";
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| - | private String available = "";
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| - | public String getAuthor() {
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| - | return author;
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| - | }
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| - | public void setAuthor(String author) {
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| - | this.author = author;
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| - | }
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| - | public String getTitle() {
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| - | return title;
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| - | }
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| - | public void setTitle(String title) {
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| - | this.title = title;
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| - | }
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| - | public String getAvailable() {
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| - | return available;
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| - | }
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| - | public void setAvailable(String available) {
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| - | this.available = available;
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| - | }
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| - | }
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| - | </source>
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| - | This is our bean. It is a simple java class. Has no argument constructor. It implements the <b>Serializable</b> interface. We have three properties of a Bean. Each of the property names begins with small letter. Each of the accessor methods is public. The properties are private.
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| - | The accessor methods consists of two parts. The first part begins with get, set or is and the second part is the name of the property with first letter capitalized.
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| - | <source lang="java">
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| - | <%@page contentType="text/html" pageEncoding="UTF-8"%>
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| - | <html>
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| - | <head>
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| - | <title>Show</title>
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| - | <link rel="stylesheet" href="style.css" type="text/css">
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| - | </head>
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| - | <body>
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| - | <jsp:useBean id="MyBean" class="com.zetcode.MyBean" scope="page">
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| - | <jsp:setProperty name="MyBean" property="author" param="author" />
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| - | <jsp:setProperty name="MyBean" property="title" param="title" />
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| - | <jsp:setProperty name="MyBean" property="available" param="available" />
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| - | </jsp:useBean>
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| - | <jsp:getProperty name="MyBean" property="author"/><br>
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| - | <jsp:getProperty name="MyBean" property="title"/><br>
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| - | <jsp:getProperty name="MyBean" property="available"/>
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| - | </body>
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| - | </html>
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| - | </source>
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| - | The show.jsp page sets the parameters into the bean and prints them.
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| - | <source lang="java">
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| - | <jsp:useBean id="MyBean" class="com.zetcode.MyBean" scope="page">
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| - | ...
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| - | </jsp:useBean>
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| - | </source>
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| - | We use this element to declare that our JSP page will use a bean. The id parameter identifies the bean. The class parameter is a fully clasified classname. The scope parameters sets the bean validity for this page only.
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| - | <source lang="java">
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| - | <jsp:getProperty name="MyBean" property="author"/><br>
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| - | </source>
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| - | This element retrieves the author property from the bean.
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| - | == Another Bean ==
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| - | Next we modify our previous example a bit.
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| - | <source lang="java">
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| - | <%@page contentType="text/html" pageEncoding="UTF-8"%>
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| - | <html>
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| - | <head>
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| - | <title>Show</title>
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| - |
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| - | <link rel="stylesheet" href="style.css" type="text/css">
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| - | </head>
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| - | <body>
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| - | <jsp:useBean id="MyBean" class="com.zetcode.MyBean" scope="page">
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| - | <jsp:setProperty name="MyBean" property="*"/>
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| - | </jsp:useBean>
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| - | <jsp:getProperty name="MyBean" property="author"/><br>
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| - | <jsp:getProperty name="MyBean" property="title"/><br>
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| - | <jsp:getProperty name="MyBean" property="available"/>
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| - |
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| - | </body>
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| - | </html>
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| - | </source>
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| - | We slightly change the show.jsp page.
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| - |
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| - | <source lang="java">
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| - | <jsp:setProperty name="MyBean" property="*"/>
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| - | </source>
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| - | This element will automatically fill the bean properties with the request parameters. This works only if the parameter names match the bean property names.
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| - | [[Категория:Java]]
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