Servlet and JSP final review examination site sorting 42 questions and 42 answers

JSP Examination site 42 ask 42 answer

JSP Servlet Introduce

How to create Sevlet Class and create Servlet Class in three ways

Realization Servlet Interface , Inherit GenericServlet class , Inherit HTTPServlet

How to sign up Servlet（web.xml And annotation methods ）

xml The way

 <servlet>
     <servlet-name>MyServlet</servlet-name>
     <servlet-class>net.biancheng.www.MyServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/MyServlet</url-pattern>
</servlet-mapping>

Annotation method

@WebServlet("/MyServlet") 

stay Servlet Get request parameters （ How to obtain a single value of a parameter and multiple values of a parameter ）

public String getParameter(String paramName);	// Get a parameter 
public String[] getParameterVValues(String paramName);	// Get multiple parameters 

Servlet How it works

When Web The server received a HTTP When asked , It will judge the content of the request first —— If it's static web data ,Web The server will handle it by itself , And then generate response information ; If dynamic data is involved ,Web The server will forward the request to Servlet Containers . here Servlet The container will find the corresponding Servlet Instance to handle , The results will be sent back Web The server , Again by Web The server returns the client .

Servlet Life cycle approach 、 The function of each method 、 Number of calls, etc

GET and POST Differences in requests , about GET request , To rewrite doGet() Method , about POST request , To rewrite doPost() Method

	GET	POST
Back button / Refresh	harmless	The data will be resubmitted （ The browser should inform the user that the data will be resubmitted ）.
Bookmarks	Can be bookmarked	Can't be bookmarked
cache	Can be cached	Can't cache
The encoding type	application/x-www-form-urlencoded	application/x-www-form-urlencoded or multipart/form-data. Use multiple encoding for binary data .
history	Parameters remain in browser history .	Parameters are not saved in browser history .
Restrictions on data length	Yes . When sending data ,GET Method direction URL Add data ;URL The length of is limited （URL The maximum length of is 2048 Characters ）.	unlimited .
Restrictions on data types	Only ASCII character .	There is no limit to . Binary data is also allowed .
Security	And POST comparison ,GET It's not safe , Because the data sent is URL Part of . Never use... When sending passwords or other sensitive information GET ！	POST Than GET More secure , Because parameters are not saved in browser history or web In the server log .
visibility	The data is in URL China is visible to all .	The data will not be shown in URL in .

Servlet API And thread model

ServletConfig Objects and ServletContext Use and comparison of objects

• Use ServletContext Objects represent WEB Applications

  • In a WEB In the application , There can only be one ServletContext object
  • Every WEB Applications , All have their own counterparts ServeltContext object
  • stay WEB When the container starts , For every one of them WEB The application creates a separate ServletContext object
  • ServletContext It's the interface , The implementation class of this interface is Tomcat Provided by container

• Web The container will provide Servlet Create a corresponding ServletConfig object ,ServletConfig It stands for Servlet The object that initializes the parameter .

  obtain ServletConfig：

  ServletConfigconfig=this.getServletConfig();
  

  API

  Method	Return value	describe
  getInitParameter	String	obtain WEB Initialization parameters for the application

Define and get context parameters and Servlet Is the initialization parameter of （web.xml How to define ,Servlet How to get ）

obtain ServletContext

1. adopt ServletConfig Interface

// adopt ServletConfig Object acquisition 
ServletConfigconfig=this.getServletConfig();
ServletContextcontext2=config.getServletContext();

2. By inheritance GenericServlet obtain

// obtain ServletContext object 
ServletContextcontext=this.getServletContext();

Get initialization parameters

Definition ：

<!-- To configure WEB Initialization parameters for the application -->
<context-param>
	<param-name>bdit</param-name>
	<param-value>java</param-value>
</context-param>
<context-param>
	<param-name>version</param-name>
	<param-value>V1.0</param-value>
</context-param>

obtain ：

// obtain ServletContext object 
ServletContextcontext=this.getServletContext();
// obtain WEB Initialization parameters for the application 
Stringbdit=context.getInitParameter("bdit");
Stringversion=context.getInitParameter("version");
System.out.println(bdit);
System.out.println(version);

How to use the single thread model

Realization SingleThreadModel Interface

Manage sessions and handle errors

Four conversational techniques

• Hide form fields
• URL rewrite
• Cookie
• Session

Submit data using hidden fields

<input name="id" value="123" type="hidden"/>

How to use URL Rewrite the implementation to append parameters

url The advantage of rewriting is ：

• To shorten the url, Hide the actual path to improve security
• Easy for users to remember and type .
• Easy to be included by search engines

Use steps

1. download jar urlrewritefilter

2. To configure web.xml

<filter>
    <filter-name>UrlRewriteFilter</filter-name>
    <filter-class>org.tuckey.web.filters.urlrewrite.UrlRewriteFilter</filter-class>
    <!--<init-param> <param-name>confReloadCheckInterval</param-name> <param-value>60</param-value> </init-param> <init-param> <param-name>confPath</param-name> <param-value>/WEB-INF/urlrewrite.xml</param-value> </init-param>-->
</filter>
<filter-mapping>
    <filter-name>UrlRewriteFilter</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>FORWARD</dispatcher>
</filter-mapping>

3. To configure urlrewrite.xml

<urlrewrite>
    <rule>
       <note>.../book/1234 instead of .../book.jsp?id=1234</note>
       <from>/book/([0-9]+)$</from>
       <to>/book.jsp?id=$1</to>
    </rule>
</urlrewrite>

Realization Cookie： establish 、 Send and store 、 Delete and how to get Cookie

establish

public Cookie(String Name,String value)

send out

resp.addCookie(Cookie cookie);

Delete

Cookie cookie[] = req.getCookies();

obtain

cookie.setMaxAge(0);

Use Session Object to implement session management ： How to get a session object 、 Add attribute 、 stay servlet and jsp Page get session properties .

Get objects

req,getSession();

get attribute

public Object getAttribute(String name)

add to

public void setAttribute(String name, Object value)

How to end a session

public void invalidate()

How to configure session timeout , The timeout is negative 、0、 What does a positive value mean , What are the units .

public int getMaxInactiveInterval()
// This method returns  Servlet  The container remains when accessed by the client  session  Maximum time interval between sessions opening , In seconds .
public void setMaxInactiveInterval(int interval)
// The method in  Servlet  Indicates the container  session  Before the session is invalid , Specify the time between client requests , In seconds .

negative ： Never fail

0： Lapse immediately

Comes at a time ：……

How to configure error pages for error codes and exception types

<error-page>
    <exception-type>java.lang.Throwable</exception-type >
    <location>/ErrorHandler</location>
</error-page>

How to send a custom error status code ： call sendError() Method

public void sendError(int status);
public void sendError(int status,String message);

Common status codes （ Three position numeric code and constant name ）：200、400、404、410、500 etc.

Code	news	describe
100	Continue	Only part of the request has been received by the server , But as long as it's not rejected , The client should continue the request .
101	Switching Protocols	Server switching protocol .
200	OK	The request is successful .
201	Created	The request is complete , And create a new resource .
202	Accepted	The request was accepted for processing , But the process is incomplete .
203	Non-authoritative Information
204	No Content
205	Reset Content
206	Partial Content
300	Multiple Choices	Link list . Users can choose a link , Enter this position . Up to five addresses .
301	Moved Permanently	The requested page has been transferred to a new one URL.
302	Found	The requested page has been temporarily transferred to a new one URL.
303	See Other	The requested page can be on a different page URL Next found .
304	Not Modified
305	Use Proxy
306	Unused	Use this code in previous versions . It is no longer used , But the code remains .
307	Temporary Redirect	The requested page has been temporarily transferred to a new one URL.
400	Bad Request	The server does not understand the request .
401	Unauthorized	The requested page requires a user name and password .
402	Payment Required	You cannot use this code yet .
403	Forbidden	Disable access to the requested page .
404	Not Found	The server could not find the requested page ..
405	Method Not Allowed	The method specified in the request is not allowed .
406	Not Acceptable	The server only generates a response that is not accepted by the client .
407	Proxy Authentication Required	Before the request is delivered , You must use proxy authentication .
408	Request Timeout	The request takes longer than the server can wait , Overtime .
409	Conflict	The request could not be completed because of a conflict .
410	Gone	The requested page is no longer available .
411	Length Required	“Content-Length” Undefined . The server cannot process the client sent without band Content-Length Request information for .
412	Precondition Failed	The prerequisites given in the request are evaluated by the server as false.
413	Request Entity Too Large	The server does not accept the request , Because the request entity is too large .
414	Request-url Too Long	The server does not accept the request , because URL Too long . When you convert a “post” The request is a... With long query information “get” Occurs when a request is made .
415	Unsupported Media Type	The server does not accept the request , Because the media type is not supported .
417	Expectation Failed
500	Internal Server Error	An unfinished request . The server encountered an unexpected situation .
501	Not Implemented	An unfinished request . The server does not support the required functionality .
502	Bad Gateway	An unfinished request . The server received an invalid response from the upstream server .
503	Service Unavailable	An unfinished request . Server temporarily overloaded or crashed .
504	Gateway Timeout	gateway timeout .
505	HTTP Version Not Supported	Server does not support "HTTP agreement " edition .

Servlet Communication between 、 Filters and monitors

Understanding filters

servlet A filter is a method of intercepting requests and corresponding objects between a client and a server . Filters can be modified Web The header and content of the request sent by the client , And forward it to the target servlet.

advantage ：

• Request identification
• Request to intercept
• Validate users
• Type conversion
• Resource communication

Implement filters ： establish 、 Register and use filters , And the legality of the filter url Pattern

void init(FilterConfig config);// Used to complete Filter The initialization .

void destory();// be used for Filter Before destruction , Complete the recycling of certain resources .

void doFilter(ServletRequest request,ServletResponse response,FilterChain chain);// Realize filtering function 

Deploy ：

• filter

  <filter>
  	<display-name></display-name>		<!-- 0 or 1 individual  -->    
  	<description></description>			<!-- 0 or 1 individual  -->
  	<icon>								<!-- 0 or 1 individual  -->
  		<small-icon></small-icon>		<!-- 0 or 1 individual  -->
  		<large-icon></large-icon>		<!-- 0 or 1 individual  -->
  	</icon>
  	<filter-name></filter-name>			<!-- 1 individual  -->
  	<filter-class></filter-class>		<!-- 1 individual  -->
  	<init-param>						<!-- 0 Or more  -->
  		<description></description>		<!-- 0 or 1 individual  -->
  		<param-name></param-name>		<!-- 1 individual  -->
  		<param-value></param-value>		<!-- 1 individual  -->
  	</init-param>
  </filter>
  

• filterMapping

  <filter-mapping>						<!-- 1 Or more  -->
  	<filter-name></filter-name>			<!-- 1 individual  -->
  	<url-pattern></url-pattern>			<!-- <url-pattern> and <servlet-name> Choose any one  -->
  	<servlet-name></servlet-name>		
  	<dispatcher></dispatcher>			<!-- 0 Or more  -->
  </filter-mapping>
  

The characteristics and differences between request forwarding and response redirection , And how to implement redirection and request forwarding

Request forwarding （RequestDispatcher）： After the server receives the request , Jump from one resource to another .

Response redirection （Redirect）： The client sends a request to the server , Then the server sends the redirected status code to the client , At the same time, the client re requests the specified address from the server .

Request forwarding RequestDispatcher	Response redirection Redirect
The browser address bar does not change , It will not become the destination address	The browser address bar has changed , Become the destination address
Request forwarding is the behavior of the server , The whole forwarding process is completed in the server	Redirection is the behavior of the browser , By responding to objects HttpServletResponse To execute
The whole process is a request , One response	The whole process is two requests , Two responses
All resources are shared Request Data in domain	Do not share Request Data in domain
It can be forwarded to WEB-INF Under the table of contents	Cannot access WEB-INF Directory of resources
You cannot access resources outside the project	You can access resources outside the project

Response redirection 、forward In forwarding and include Forwarding features and differences ,sendRedirect() and forward() as well as include() Method path writing .

• RequestDispatcher
  • forward： Do not include the contents of the original page , The same request , Jump to the new 、 Separate pages , The address remains the same
  • include： Contains the contents of the original page , The same request , Or the original page , It includes something new , The address remains the same
• Redirect
  • redirect： Do not include the contents of the original page , Different requests , Jump to the new 、 Separate pages , Address change

ServletContextListener： Implementing this interface creates a context listener , Listen for the creation of context objects （ Or initialize ） And destroy , That is, the start and stop of the program .

in web.xml

<listener> 
	<listener-class>ServletContextTest.ServletContextLTest</listener-class>
</listener> 

java

public class ServletContextLTest implements ServletContextListener{
    
    //  Implement the destruction function 
    public void contextDestroyed(ServletContextEvent sce) {
    
        System.out.println("this is last destroyeed");
    }
    //  Implement the initialization function , When an event occurs, it triggers 
    public void contextInitialized(ServletContextEvent sce) {
    
        System.out.println("======listener test is beginning=========");
    }
}

JSP Introduce

JSP working principle ： The first request is converted to Servlet, And compile , Subsequent requests will not be converted and compiled .

jspInit();//servlet  Call... On initialization 
jspService();// Called when a request is received 
jspDestroy();// Remove... From the service servlet Previous call 

JSP Implicit objects ： What implicit objects are there , And how the four domain objects add and get attributes .

SP The implicit object is JSP The container provides for each page Java object , Developers can use them directly without explicitly declaring .JSP Implicit objects are also called predefined variables .

JSP The nine implicit objects supported ：

object	describe
request	HttpServletRequest An instance of an interface .request Object provides a series of methods to get HTTP Header information ,cookies,HTTP Methods, etc. .
response	HttpServletResponse An instance of an interface .response Object also defines the process HTTP Interface of head module . Through this object , Developers can add new cookies, Time stamp ,HTTP Status codes, etc .
out	JspWriter Class , Used to output the results to the web page .
session	HttpSession Class .
application	ServletContext Class , Related to the application context .
config	ServletConfig Class .
pageContext	PageContext Class , Provide right JSP Access to all objects and namespaces on the page .
page	Be similar to Java Class this keyword .
Exception	Exception Class object , It means something is wrong JSP The corresponding exception object in the page .

Four domain objects ：

Class name	domain name	function
ServletContext	context Domain	 Save... On the entire server , All users can use . Invalid after restarting the server JSP Built-in objects
HttpSession	session Domain	Once again, the session is valid . Server jump 、 Client jumps are valid . Closing and reopening the web page is invalid
HttpServletRequet	request Domain	Valid only in one request , Valid after server jump . Invalid client hop
PageContext	page Domain	Save properties in only one page . No effect after jump .

application.setAttribute("application","application");
session.setAttribute("session","session");
request.setAttribute("request","request");
pageContext.setAttribute("pageContext","pageContext");

application.getAttribute("application");
session.getAttribute("session");
request.getAttribute("request");
pageContext.getAttribute("pageContext");

JSP Script elements ： expression 、Scriptlet（ Code segment ） And the statement

<%!
	int a=0;
	String s="w31q2";
	// Statement ： Define variables and methods 
%>
<%= expression %> 
<%--  expression ： Insert values directly into the output  --%>
<%
	// direct writing Java Code 
%>

Custom tags

How to create a custom tag , Including empty tags and tags with attributes

public class ClassName extends BodyTagSupport{
    
	int	doAfterBody()
    int	doEndTag()
    void doInitBody()
    int	doStartTag()
    BodyContent	getBodyContent()
    JspWriter	getPreviousOut()
    void release()
    void setBodyContent(BodyContent b)
}

TLD How to describe tag library and tag and tag attributes in the file

<?xml version="1.0" encoding="ISO-8859-1" ?>
<!—XML And its character set -->
<!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.1//EN" 　"http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_1.dtd">
<!— Document type definition -->
<taglib>
<!— This tag indicates that we are beginning to describe a tag library -->
	<tlibversion>1.0</tlibversion>
    <!— The version of the tag library -->
    <jspversion>1.1</jspversion>
    <!— What is used JSP Version of -->
    <shortname>tagclass</shortname>
    <!— Default name --> 	 
    <tag>
        <name>login</name>
        <!— The name of the tag -->
        <tagclass>
        	tagclass.login.login
        	<!— Deal with this Tag The name of the corresponding class of -->
        </tagclass>
        <info>
            <!— Description of this marker -->
        </info>
		<attribute>
            <!— Start defining tag attributes -->
      　　　　<name>height</name>
　　　　　　　	<!— Name of property -->
      　　　　<required>true</required>
　　　　　　　	<!— Indicates whether this attribute is required -->
      　　　　<rtexprvalue>true</rtexprvalue>
			<!— Indicates whether this attribute can be used JSP The result output of the program segment -->
   　　　</attribute>
		<attribute>
      　　　　<name>width</name>
      　　　　<required>true</required>
      　　　　<rtexprvalue>true</rtexprvalue>
   　　　</attribute>
    </tag>
</taglib>

stay JSP Pages introduce tag libraries and use tags

<%@ taglib uri="URIToTagLibrary" prefix="tagPrefix" %>
<%@ taglib uri="/tlds/taglib.tld" prefix="tagclass" %>
<html>
    <head>
        <title>login</title>
    </head>
    <body>
        <tagclass:login width="200" height= "100" >
        </tagclass:login>
    </body>
</html>

doStartTag()、doAfterBody() Methods and doEndTag() Return value of method

How to use markup files / Label files create custom tags , How to use a custom tag after creating it

In the catalog ：’Web The server \WEB-INF\tags‘ Create and store xxx.tag Of tag file

wel.tag

<%@ tag language="java" pageEncoding="UTF-8"%>
<p> This is a Tag file , Responsible for calculation 1～100 The sum of odd numbers in :</p>
<%--  Write properties here  --%>
<%@attribute name="message" required="true" %>
<h3>{message}<h3>

.jsp

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!--
 Use <taglib> The instruction tag introduces the Web Tag library under service directory , That's the only way ,JSP Pages can be used Tag The tag invokes the corresponding Tag file .<taglib> The format of the instruction is as follows :
    <％@ taglib tagdir=" Custom tag library location " prefix=" Prefix "> 
-->
<%@taglib tagdir="/WEB-INF/tags" prefix="my" %>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>JSP Page</title>
    </head>
    <body bgcolor="cyan">
        <h3> Here is the call Tag The effect of the document :</h3>
        <my:/>
    </body>
</html>

<jsp:doBody> The function of action

doBody Action elements can only be used in tag file Use in , It is used to call the contents of the tag body of a tag

doBody Action elements can also have attributes . you You can use these attributes to specify a variable to receive the contents of the label body , If you do not use these instructions , that **doBody The action element will write the contents of the tag body to JSP Page JspWriter On **.

attribute	describe
var	The variable value used to save the contents of the label body , The contents of the label body will be marked with java.lang.String Type saved to this var In variables .var and varReader Only one property can appear
varReader	The variable value used to save the contents of the label body , The contents of the label body will be marked with java.io.Reader Type saved to this varReader In variables .var and varReader Only one property can appear
scope	Scope to which the variable is saved

Design patterns and JDBC API Introduce

understand Dao Design patterns

Dao Patterns combine object persistence with database access logic or persistence mechanisms API Separate . This design pattern allows you to modify the database access code at any time without modifying the application code

understand MVC Design patterns ： Full name 、 Each component and its role

The model layer （Model）： An object model abstracted from the real world , It is the reaction of applied logic ; It encapsulates data and operations on data , It is the place where data processing is actually carried out （ The model layer interacts with the database ）

View layer （View）： It is the interface between application and user , It is responsible for displaying the application to the user and Displays the status of the model .

controller （Controller）: The controller is responsible for the interaction between the view and the model , Controls the response to user input 、 Response mode and process ; It's mainly responsible for two aspects of movement , One is to distribute the user's request to the corresponding model , Second, model changes should be reflected in the view in a timely manner .

Develop scriptless JSP page

Use EL Expression to get request parameters

${request.param}

Use EL Expression acquisition Cookie Value

${cookie.param.value}

Use EL Expression to get context parameters

${context.param}

EL How expressions handle null values

General situation ： As “”

Arithmetic expressions ： As 0

Logical expression ： As false

Usage function EL Expression to get the attribute in the domain object

EL The expression will be based on id Go to User Class to find this id Of get Method , At this time, it will automatically id Capitalize and add get Prefix , Once you find a way to match it ,El The expression will think that this is the attribute to be accessed , And return the value of the property .

JSTL Core tag library ：c:set, c:if, c:when, c:choose, c:otherwise, c:forEach Tag usage and attributes .

c:set

<c:set
   var="<string>"
   value="<string>"
   target="<string>"
   property="<string>"
   scope="<string>"/>

<c:set> Tags have the following properties ：

attribute	describe	Is it necessary?	The default value is
value	Value to store	no	The content of the subject
target	The object to which the property to modify belongs	no	nothing
property	Properties to modify	no	nothing
var	Variables that store information	no	nothing
scope	var The scope of the property	no	Page

c:if

<c:if test="<boolean>" var="<string>" scope="<string>">
   ...
</c:if>

<c:if> Tags have the following properties ：

attribute	describe	Is it necessary?	The default value is
test	Conditions	yes	nothing
var	Variables used to store conditional results	no	nothing
scope	var The scope of the property	no	page

c:when && c:choose $$ c:otherwish

<c:choose>
    <c:when test="<boolean>">
        ...
    </c:when>
    <c:when test="<boolean>">
        ...
    </c:when>
    ...
    ...
    <c:otherwise>
        ...
    </c:otherwise>
</c:choose>

<c:when> The attributes of the tag are as follows ：

attribute	describe	Is it necessary?	The default value is
test	Conditions	yes	nothing

c:forEach

<c:forEach
    items="<object>"
    begin="<int>"
    end="<int>"
    step="<int>"
    var="<string>"
    varStatus="<string>">

<c:forEach> Tags have the following properties ：

attribute	describe	Is it necessary?	The default value is
items	Information to be recycled	no	nothing
begin	The starting element （0= First element ,1= The second element ）	no	0
end	The last element （0= First element ,1= The second element ）	no	Last element
step	Step length of each iteration	no	1
var	Represents the variable name of the current entry	no	nothing
varStatus	The name of the variable that represents the state of the loop	no	nothing

JSTL Formatting common tags for tag libraries ：formatNumber

<fmt:formatNumber
  value="<string>"
  type="<string>"
  pattern="<string>"
  currencyCode="<string>"
  currencySymbol="<string>"
  groupingUsed="<string>"
  maxIntegerDigits="<string>"
  minIntegerDigits="<string>"
  maxFractionDigits="<string>"
  minFractionDigits="<string>"
  var="<string>"
  scope="<string>"/>

fmt:formatNumber Tags have the following properties ：

attribute	describe	Is it necessary?	The default value is
value	Number to display	yes	nothing
type	NUMBER,CURRENCY, or PERCENT type	no	Number
pattern	Specify a custom format to use with output	no	nothing
currencyCode	Currency code （ When type="currency" when ）	no	Depending on the default area
currencySymbol	Currency symbols ( When type="currency" when )	no	Depending on the default area
groupingUsed	Whether to group numbers (TRUE or FALSE)	no	true
maxIntegerDigits	The largest number of integers	no	nothing
minIntegerDigits	The smallest number of integers	no	nothing
maxFractionDigits	The largest number of digits after the decimal point	no	nothing
minFractionDigits	The smallest number of digits after the decimal point	no	nothing
var	Variables that store formatted numbers	no	Print to page
scope	var The scope of the property	no	page