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jsp Nine built-in objects

jsp Nine built-in objects , Refer to Tomcat In Translation jsp The page becomes Servlet After the source code , Nine internal objects , It's called built-in objects .

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request                  Request object

response                 The response object

pageContext          jsp Context object

session                 Conversation object

application             ServletContext object

config                     ServletConfig object

exception                 Exception object

out                          jsp Output stream object

jsp Four domain objects

  Domain objects can be Map The same object that accesses data . The four domain objects function the same , They have different access ranges to data

The four domain objects are ：

Domain object	Category	Scope of visit
pageContext	（PageContextImpl class ）	At present jsp Valid within page range
request	（HttpServletRequest class ）	Valid within one request
session	（HttpSession class ）	Valid within a session scope ( Open the browser to access the server , Until the browser is closed )
application	（ServletContext class ）	Whole web Valid within the scope of work ( as long as web The project doesn't stop , The data are all there )

// Data is saved to each of the four fields

<%

        pageContext.setAttribute("key","pageContext");

        request.setAttribute("key","request");

        session.setAttribute("key","session");

        application.setAttribute("key","application");

%>

pageContext Whether the field has a value ：<%=pageContext.getAttribute("key")%> <br>

request Whether the field has a value ：<%=pageContext.getAttribute("key")%> <br>

session Whether the field has a value ：<%=session.getAttribute("key")%> <br>

application Whether the field has a value ：<%=application.getAttribute("key")%> <br>

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  Create another jsp page ：

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  Other scope tests ：

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  They range from small to large , When using, generally use a small range first , Small range is not enough for reuse .( Reasons for memory optimization )

Small ：pageContext

request

session

Big ：application

jsp Medium out Output and response.getWriter The difference in output

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  We can find out , Whoever outputs the results before , All are response First

Graphic analysis ：

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  When jsp On the page All code execution completed What will be done later ：

1、 perform out.flush() operation , Will be able to out The data of the buffer is appended to the response End of buffer .

2、 Will execute response Refresh operation of , Write data to the client .

verification ：​ edit  

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  because jsp After translation , The underlying source code uses out To output , So in general , We are jsp Unified use of pages out For the output . Avoid disrupting the order of page output .

out.print() and out.write() 

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out.write() The output string is OK

out.print() Any data can be output （ Will be converted to a string after calling write Output ）

Conclusion ： stay jsp On the page , Can it be used uniformly out.print() To output

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