Si Wen's innovative interview questions

The answer to the first question is as follows:

JSP has 9 built-in objects. The simple memory method is: remember one word: parscope oscilloscope, which includes: page, application, request, response, session, config, out, pagecontext, exception.

1. The request information of the request object client is encapsulated in the request object, through which we can know the customer's needs and then respond. It is an example of the HttpServletRequest class.

1.objectgetattribute (stringname) returns the property value of the specified property.

2.Enumeration getAttributeNames () returns an enumeration of all available attribute names.

3.String getCharterencoding () returns the character encoding method.

4.int getcontentlength () returns the length of the request body (in bytes).

5.String getContentType () gets the MIME type of the request body.

6. ServletInputStream getInputStream () gets the binary stream of one line in the request body.

7. String getparameter (String name) returns the parameter value of the parameter specified by name.

8. Enumeration getParameterNames () returns an enumeration of available parameter names.

9. String [] getParameterValues (StringName) returns an array containing all the values of the parameter names.

10.String getProtocol () returns the protocol type and version number used for the request.

11.stringetscheme () returns the plan name used for the request, such as http.https and ftp.

12.String getServerName () returns the host name of the server accepting the request.

13.int getServerPort () returns the port number used by the server to accept this request.

14. BufferedReader getReader () returns the decoded request body.

15.String getRemoteAddr () returns the IP address of the client that sent this request.

16.String getRemoteHost () returns the host name of the client that sent this request.

17. Voidset attribute (stringkey, Object obj) sets the attribute value of the attribute.

18.stringetrealpath (stringpath) returns the real path of the virtual path.

2.response Object The response object contains information about responding to customer requests, but it is rarely used directly in JSP. It is an instance of the HttpServletResponse class.

1.string getchartencoding () What character encoding is used to return the response?

2.Servlet output stream getOutput Stream () returns the binary output stream of the response.

3.PrintWriter getWriter () returns an object that can output characters to the client.

4.void setContentLength(int len) sets the length of the response header.

5.Void set content type (string type) sets the MIME type of the response. 6. send redirect (java.lang.stringlocation) redirects the client's request.

3. Session object A session object refers to a session between a client and a server, starting from the client's connection to the server's web application until the client disconnects from the server. It is an instance of the HttpSession class.

1.long getCreationTime () returns the session creation time.

2.public String getId () returns the unique Id number set by the JSP engine when creating the session.

3.long getLastAccessedTime () returns the last request time of the client in this session.

4.int getmaxiinactiveinterval () returns the time interval between two requests. This session has been cancelled (milliseconds).

5.String[] getValueNames () returns an array containing all the properties available in this session.

6.VoidInvalid () cancels the session and makes it unavailable.

7.boolean isNew () returns the session created by the server and whether the client has joined.

8.void removeValue (string name) deletes the attribute specified in the session.

9. VoidsetMaxinACTIVE INTERVAL () sets the time interval between two requests. This session was cancelled (milliseconds).

4.out Object The out object is an instance of the JspWriter class, which is a general object used to output content to the client.

1.void clear () clears the contents of the buffer.

2.void clearBuffer () clears the current contents of the buffer.

3.void flush () empties the stream

4.int getBuffersize () returns the size of the buffer in bytes, or 0 if there is no buffer.

5.int getRemaining () returns how many buffers are available.

6.boolean isAutoFlush () returns whether to empty the buffer automatically or throw an exception when the buffer is full.

7.void close () closes the output stream

5.page object page object refers to the current JSP page itself, a bit like this pointer in the class. It is an instance of the java.lang.Object class.

1.class getClass returns the class of this object.

2.int hashcode () returns the hash code of this object.

3.boolean equals(Object obj) determines whether the object is equal to the specified object.

4.void copy(Object obj) copies this object to the specified object.

5.Object clone () clones this object.

6.String toString () converts this object into an object of class String.

7.void notify () wakes up a waiting thread.

8.void notifyAll () wakes up all the waiting threads.

9.void wait(int timeout) makes the thread wait until the timeout ends or it is awakened.

10.void wait () keeps the thread waiting until it is awakened. 1 1. Lock the object.

12.void exitMonitor () unlocks the object.

6. Application object Application object realizes data sharing between users and can store global variables. It starts when the server is started and ends when the server is shut down. In the meantime, this object will always exist; In this way, the same property of this object can be operated in the connection between users or between different users; Operations on this object property anywhere will affect other users' access to it. The startup and shutdown of the server determines the life of the application object, which is an instance of the ServletContext class.

1.objectgetattribute (stringname) returns the property value of the given name.

2.Enumeration getAttributeNames () returns an enumeration of all available attribute names.

3.Void set attribute (String name, Object obj) sets the attribute value of the attribute.

4. Delete attribute (string name) Delete an attribute and its attribute value.

5.String getServerInfo () returns the JSP(SERVLET) engine name and version number.

6.String getRealPath(String path) returns the real path of the virtual path.

7. ServletContext getContext (String UriPath) returns the application object of the specified WebApplication.

8.int getmajorversion () returns the maximum version number of Servlet API supported by the server.

9.int getminor version () returns the maximum version number of Servlet API supported by the server.

10.stringtime type (stringtile) returns the MIME type of the specified file.

11.urlgetresource (stringpath) returns the URL path of the specified resource (file and directory).

12.inputstream getresourcestream (string path) returns the input stream of the specified resource.

13. request dispatcher getrequestdispatcher (string uri path) returns the requestdispatcher object of the specified resource.

14.servlet getservlet (stringname) returns the servlet with the specified name.

15.enumeration getservlet () returns an enumeration of all Servlet.

16.enumeration getServletnames () returns an enumeration of all servlet names.

17.void log (string msg) writes the specified message to the log file of the Servlet.

18. Voidlog (ExceptionException, string msg) writes the stack trace and error message of the specified exception to the Servlet log file.

19.Voidlog (String MSG, Throwable Throwable) writes the description information of stack trace and Throwable exception into Servlet log file.

7. exception Object An exception object is an exception object generated when an exception occurs in the process of page running. If a JSP page wants to apply this object, it must be set to true, otherwise it cannot be compiled. It is actually an object of java.lang.Throwable

1. string message () returns a message describing the exception.

2.String toString () returns a short description message about the exception.

3.void printStackTrace () shows the exception and its stack trace.

4.Throwable fill stack trace () rewrites the execution stack trace of the exception.

Eight. PageContext object pageContext object provides access to all objects and namespaces in JSP pages, that is, it can access the session where the page is located, or it can take an attribute value of the application where the page is located. It is equivalent to the epitome of all functions in the page, and its class name is also called pageContext.

1.JspWriter getOut () returns the JspWriter stream (Out) used by the current client response.

2.HttpSession getSession () returns the HttpSession object (session) in the current page.

3.Object getPage () returns the object (page) of the current page.

4.ServletRequest getRequest () returns the ServletRequest object (request) of the current page.

5.ServletResponse getResponse () returns the ServletResponse object (Response) of the current page.

6. Return the Exception object of the current page.

7. ServletConfig getServletConfig () returns the ServletConfig object (config) of the current page.

8. servlet context getServletContext () returns the ServletContext object (application) of the current page.

9.Void Set Attribute (string name, object attribute) sets attributes and attribute values.

10. Voidset Attribute (String Name, Object obj, Intscope) sets the attributes and attribute values within the specified range.

1 1. The public object getattribute (string name) takes the value of the attribute.

12. objectgetattribute (stringname, Intscope) adopts attribute values within the specified range.

13. the public object Find Attribute (String Name) finds the attribute and returns the attribute value or NULL.

14.void remove attribute (string name) deletes an attribute.

15. Delete the attributes within the specified range.

16.int getattributescope (stringname) returns the range of attributes.

17.enumeration getattributenamesinscope (intscope) returns an enumeration of available attribute names within the specified range.

18.void release () releases the resources occupied by pageContext.

19.Voidforward (string relative URL path) redirects the current page to another page.

20.Void include (string relative URL path) contains another file in the current location.

The 9.JSP engine uses the config object to transmit information to the Servlet when it is initialized. This information includes the parameters used when initializing the Servlet (consisting of attribute names and attribute values) and information about the server (by transferring ServletContext objects).

1.servlet context getServletContext () returns a ServletContext object containing server information.

2. String get init parameter (String name) returns the value of initialization parameter.

3. Enumeration getinitParameterNames () returns an enumeration of all parameters required for Servlet initialization.