'Back-End/Jsp'에 해당되는 글 14건

Page directives

- The jsp directives are messages that tells the web container how to translate a JSP page into the corresponding servlet

1. Syntax

<%@ directive attribute="value" %>

2. page directive

- The page directive defines attributes that apply to an entire JSP page

2_1. Syntax

<%@ page attribute="value" %>

2_2. Attributes

• import
• contentType
• extends
• info
• buffer
• language
• isELIgnored
• isThreadSafe
• autoFlush
• session
• pageEncoding
• errorPage
• isErrorPage

2_3. How to use

1) import

- It is used to import class, interface or all the members of a package

- It is similar to import keyword in java class 

Example

2) contentType

- The contentType attribute defines the MIME(Multipurpose Internet Mail Extension) type of the HTTP response

- Default value is "text/html; charset-ISO-8859-1"

Example

- When I reload the welcome.jsp page, welcome.jsp page is downloaded

3) buffer

- The buffer attribute sets the buffer size in kilobytes to handle output generated by the JSP page

- The default size of the buffer is 8Kb

Example

4) isELIgnored

 - We can ignore the Expression Language(EL) in jsp by the isELIgnored attribute

- By default its value is false i.e. Expression Language is enabled by default

Example

5) errorPage

- The errorPage attribute is used to define the error page, if exception occurs in the current page, it will be redirected to the error page

Example

6) isErrorPage

- This attribute is used to declare that the current page is the error page

Example

Implicit Object_2

1. application implicit

- application is an implicit object of type ServletContext

- The instance of ServletContext is created only one by the web container when application or project is deployed on the server

- This object can be used to get initialization parameter from configuration file(web.xml)

1_1 index.html

1_2. web.xml

1_3. welcome.jsp

2. session implicit

- The Java developer can use this object to set, get or remove attriute or to get session info

2_1. index.html

2_2. welcome.jsp

2_3. second.jsp

3. pageContext implicit

- The pageContext object can be used to set, get or remove attribute from one of the following scopes

• page
• request
• session
• application      

3_1. index.html

3_2. welcome.jsp

3_3. second.jsp

4. page implicit

- This object is assigned to the reference of auto generated servlet class

Object page = this;

4_1. Example

<% (HttpServlet)page.log("message"); %>

- You can use this object directly in jsp

<% this.log("message"); %>

5. exception implicit

- This object can be used to print the exception. But it can only be used in error pages. 

5_1. error.jsp

 Implicit Objects_1

- There are 9 jsp implicit objects. These objects are created by the web container that are available to all the jsp pages

1. out implicit object

- For writing any data to the buffer, JSP provides an implicit object named out

1_1 Servlet

1_2. JSP

2. request implicit object

- It can be used to get request information such as parameter, header information, remote address, server name, server port, content type, character encoding etc

- It can also be used to set, get and remove attributes from the jsp request scope

2_1. index.html

2_2. welcome.jsp

3. response implicit object

- It can be used to add or manipulate response such as redirect response to another resource, send error etc

3_1. index.html

]

3_2. welcome.jsp

4. config implicit object

- This object can be used to get initialization parameter for a particular JSP page

4_1. index.html

4_2. web.xml

4_3. welcome.jsp

JSP tag

- scriptlet tag

- expression tag

- declaration tag

1. scriptlet tag

<% java source code %>

1_1 Example

1) index.html

2) welcome.jsp

2. expression tag

- The code placed within Jsp expression tag is written to the output stream of the response

- It is mainly used to print the values of variable or method

<%= statement %>

2_1 Example

3. declaration tag

- The JSP declaration tag is used to declare fields and methods

- The code written inside the jsp declaration tag is placed outside the service() method  of auto generated servlet so it doesn't get memory at each request

<%! field or method declaration %>

3_1. Example