Programming Blog

Java Collection Framework

????????????????????�????????????????????????????????????????????????????????????????????�????????? ???????????????????????????????????????????????????

????????? ??????????????????????????????????????? 7 interface ??????????????????

??�????????????????????� 13 Class ???????????? implements Interface ????????�???????????????????????? ??�????????????????????????????????????????????????????????????

????????? ??????????????�??????????????? Collections ??????????????????????????????

• Lists ?????????????????????????????? implements ??????????????� List
• Sets ?????????????????????????????? implements ??????????????� Set ?????????????????????????????????????????????????????? Unique things
• Maps ?????????????????�?????? Set ??�??????????????? ID ???????????? Unique
• Queues

??�???????????????????????????????????????????????? ??????????????????????????? ????????� ????????? sorted, unsorted, ordered and unordered

Ordered
??????????????? Collections ????????????????????????????????? ordered ????????????????????? ?????????????????? interate ???????????????????????? Collections ???????????????????????�????????�????????????????????? ???????????? Array ??????????????????????????????????????????????????????????????�??????????????? ?????????????????? index ????????????????????????????????�???????????????????????????

Sorted
??????????????�?????? sorted ???????????????????????�????????????????????????????????????????????? Collection ???????????? ????????????????????????????????????????????????????????�??????????????????????????????????????????????????????????????�??????????????? Collections

List Interface
???????????? interface ????????????????????????????????? index ??????????????�?????�????????????????????????????????? List ??�?????? non-List ????????? ??????????????? method ??????????????�??????????????�?????? index ???????????? get(index), indexOf(index) ????????????????????�????????? Class ????????? implemetns ????????????????????????????????????????????? ordered ???????????? index position

ArrayList
?????????????????????????????? Array ??????????????????????????????????????????????????????????????????????????????????????? ????????????????????????????????????????????�?????? interate ??�????????�?????? ramdom access ?????????????????????????????? ????????????????????????????????? ???????????�?????? orderd ????????? index ??�???????????????????????????????????????????????? sorted ????????????????????� Java 1.4 ArrayList ????????? implements interface ????????? RandomAccess ??�????????????????????� ????????????????????? ArrayList ??�?????? LinkedList ????????? ArrayList ???????????????????????�???????????????????????????????????????????????�?????? interate

Vector
Vector ??????????????????????????????????????????????????? ArrayList ??�?????? ?????????????????????????????????????????? synchronized ??�?????? thread safety

LikedList
Likedlist ????????????????????????????????? ordered ????????? index position ????????????????????????????????????????????????????????�?????? ArrayList ??�??????????????????????????????????????????????????�?????? insert, delete ?????????????????�????????? ????????????????????????????????????????????????????????? LikedList ???????????????????????? node ??�???????????? Java 5.0 ???????????????????????????????????�?????? implements Queue ??????????????????????????� ?????????????????????????????????????????? method ????????? Queue ?????????????????�

Set Interface
???????????????????????????????????????????????? ???????????????????????? unique ???????????????????????????????????? object ????????????????????�??????

HashSet
HashSet ?????????????????????????????????????????? ???????????? ordered ??�?????? sorted ????????? Hashcode ????????�?????? insert ??????????????????????????? implement hashcode ????????????????????????????????? ??�????????????????????????????????????????????????????????????????????????????????�???????????????????????????????????? ??????????????? Collection ???????????�?????????????????????????????????????????�??????????????? object ????????????????????????????????????????????????????????�?????? ??�????????????????????????????????�?????? ??????????????????????????? ???????????? ordered ??�?????? sorted

LinkedHashSet
LinkedHashSet ??????????????????????????�?????? HashSet ??�?????????????????? ??????????????????????????? Ordered ?????????????????????????????�?????? LikeList ??????????????? LinkedHashSet ??�?????????????????????????????????????????�??????????????? object ???????????????????????�????????�???????????????????????????????????????????????? ordered

TreeSet
TreeSet ???????????? 1 ?????? 2 Collection ??????????????????????????????????????????Sorted ????????�??????????????????????????? TreeMap, TreeSet ??????????????????????????????????????�?????? Red-Black Structure ?????????????????????????????????????????????????????????????????????????????????????????? object ???????????? interate ????????�??????????????????????????�?????? ascending ???????????????????????????????????????????????????????????�???????????? ?????????????????? Class Comparator ??�?????? Comparable ????????????????????�????????????????????????????????????

MapInterface
MapInterface ??????????????????????????????????????????????????? unique ?????????????????????????????�??????????????????????????�?????? ???????????????????????? ??????????????? key/value ????????�???????????????????????? ???????????????????????�????????�?????? search Map ??????????????? method equals() ????????�?????? ??????????????????

HashMap
HaspMap ?????????????????????????????????????????????????????? ordered ??�?????? sorted ??�?????????????????? Map ???????????????????????�????????�??????????????? ?????? overhead ?????????????????????????????? ????????????????????�?????? hashset ?????????????????? implement hashcode() ????????�??????????????? ???????????????????????????????????�??????????????????????????????????????????????????? HashMap ??????????????????????????? Object ????????????????????? null ?????????

HashTable
??????????????????????????�?????? Vector ???????????????????????????????????????????????? synchronized ??�?????? HashTable ????????????????????????????????????????????? ????????????????????? null ?????????

LinkedHashMap
??????????????????????????�?????? LinkedHashSet ????????????????????????????????? insert ???????????????????????�????????? HashMap

TreeMap
??�???????????????????????�?????????????????????????????�?????? TreeSet ????????? ????????????????????????????????? sorted

QueueInterface
??�???????????????????????�?????? ??�?????????????????????????????? Queue ????????????????????? ????????? FIFO (first in first out) Queue ???????????????????????? mehtod ????????? Collection ????????????????????? ???????????? add ???????????? delete ????????�

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Java object serialization

??????????????????????????????????????????????????????????????????????????? ?????????????????????????????�???????????????????????�???????????????????????????????????????????????????????????????????????????????????? ??�?????????????????????????????????????????????????????????????????�?????? write ???????????? read object ?????�???????????????????????????????????�??????????????? write ???????????????????????? database ??�???????????????????????? write object ???????????? reference ????????? object ???????????????????????????????????????????????????????????�?????�???????????�?????? ??????????????????????????�????????�???????????????????????????????????? Serializable ????????? ????????�????????????????????? RMI (Remote method interface) ??????????????????????????????????????�?????? ????????? object ???????????????????????� JVM ?????????????????????????????????????????? Serialize object ????????????????????? ????????????????????? object ??????????????????????????????????????? ???????????? ????????????????????????????????????

??�??????????????�?????? Serialization ??????????????????????????????????????�?????? implemet interface ??????????????????

public class MySerializableClass implements Serializable{
...
}

????????????????????? Class ???????????�????????????????????????????????????????????� Serialize ??�?????????

??????????????????????????�??????????????? Object serialization SerializeDog.java

??�????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????????????????????????????????????????? ?????????????????? Class Collar

class Collar implements Serializable{
...
}

????????????????????????????????????????????�????????????????????? object Dog ???????????? ??�????????? Class Dog ????????????????????????????????? has-a Collar ????????????????????? ???????????????????????????

class Dog implements Serializable {

private Collar theCollar;

??????????????????????????? implementes Serializable ???????????�?????? Class Collar ????????????????????????????????????????????????????????????

before: collar size is 3
java.io.NotSerializableException: th.co.noppanit.Collar…

????????????????????????????????�??�???????????�?????????????????????????????????????????? ???????????? ????????? Class Collar extends Class Dog ??�???????????????????????? ??????????????????????????? Serialize ????????�??????????????????????????????????????? ??�????????????????????????????????????????????????????????? ?????????????????�???????????????????????????????????? ???????????????????????????????????????????????????????????? ??�??�???????????? Class Collar ?????????????????? ?????????????????�??�?????�???????????? ????????? modified transient ????????????????????�????????????????????????????????�???????????????????????????????????? ??�???????????????????????????????????????????????????

class Dog implements Serializable {

transient private Collar theCollar;

before: collar size is 3
Exception in thread “main” java.lang.NullPointerException at th.co.noppanit.SerializeDog.main(SerializeDog.java:24)

?????????????????????????????????????????�????????�??�??????????????????????????? SerializeDog_Mo.java

??�???????????????????????????????????????

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Regular Expressions

Regular Expression

?????????????????????????????????????????????????????????????????? ?????????????????? ????????????????????�???????????????????????????????????? ??�??????????????? ??????????????????????????????????????????????????????????????????????????????

Character Classes
1 [abc]	????????? ???????????????????????????????????????????????? a, b, or c
1 [^abc]	????????????????????????????????????????????????????????? ?????�???????????? a,b or c
1 [a-zA-Z]	??????????????????????????�???????????????????????�?????? a-z ??�???????????�???????????� case
1 [a-d[m-p]]	???????????�??????????????? a-d ?????? union ??�?????? m-p
1  [a-z&&[def]]	?????????????????? a-z ?????? union ??�?????? d,e or f
1 [a-z&&[^bc]]	???????????�??????????????? a-z ??????????????�?????? b,c
1 [a-z&&[^m-p]]	?????????????????? a-z ??????????????�?????? m-p

??�??????????????�???????????????

Predefined Character Classes
1 .	??????????????????????????????????????????????????? ??�????????????
1 \d	?????????????????????????????? 1 [0-9]
1 \D	??????????????????????????????????????? 1 [^0-9]
1 \s	???????????? whitespace 1 [ \t\n\x0B\f\r]
1 \S	????????????????????? whitespace 1 [^\s]
1 \w	????????????????????�?????�??????????????? 1 [a-zA-Z_0-9]
1 \W	?????????????????????????????�?????�??????????????? 1 [^\w]

??�????????????????????? quantifiers

Quantifiers			Meaning
Greedy	Reluctant	Possessive
1 X?	1 X??	1 X?+	1 <em>X</em> , once or not at all
1 X*	1 X*?	1 X*+	1 <em>X</em> , zero or more times
1 X+	1 X+?	1 X++	1 <em>X</em> , one or more times
1 X{n}	1 X{n}?	1 X{n}+	1 <em>X</em> , exactly 1 n times
1 X{n,}	1 X{n,}?	1 X{n,}+	1 <em>X</em> , at least 1 n times
1 X{n,m}	1 X{n,m}?	1 X{n,m}+	1 <em>X</em> , at least 1 n but not more than 1 m times

??????????????????

Boundary Matchers
1 ^	The beginning of a line
1 $	The end of a line
1 \b	A word boundary
1 \B	A non-word boundary
1 \A	The beginning of the input
1 \G	The end of the previous match
1 \Z	The end of the input but for the final terminator, if any
1 \z	The end of the input

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What is foo and bar in programming

?????????????????? ???????????????????????? ???????????????????????????????????????????????? ??�??????????????? ????????????????????? ?????????????????�??????????????????????????????????????????????????�?????? ????????? ????????� programming ?????????????????????????????????????????????????????? foo and bar ????????????????????�??????????????�??�????????? ???????????????????????? ???????????????????????? ???????????? method ???????????? ???????????????????????�?????? ??�??????????????�??????????????? foo and bar ??�????????????????????????????????? ?????????????????? ???.???.??�????????�??????

????????�????????? ??????????????????????????�??�??????????????? FUBAR (???Fucked Up Beyond All Repair??? or ???Fucked Up Beyond All Recognition???) ??�?????????????????????????????? ????????�?????�???????????????????????� ??�???????????�????????�?????????????????? ??�??????????????????????????????????????????????????????????????�???????????????????????????????????�??????????????????????????????????????????????????? FOOBAR ??�???????????????????????�????????????????????????????????? ??????????????????????????????????????????????????????????????? ????????????????????????????????�?????? ???????????? ??????????????�?????????????????????????????????????????????????????�?????????????????�??????????????? ??????????????�?????�??????????????? ??????????????�????????????????????? ????????? fu ???????????�???????????????????????????????????? ?????????????????? ?????????????????????????????� Warner Brothers Cartoon Companion ??????????????�?????????????????� ????????�?????????????????????????????????????????????????????�?????????????????????????????????????????? Foo-fighter ??�????????????????????�??????????????? ????????????????????????

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Common struts error

This page contains errors and exceptions commonly encountered during web application development using Struts. Along with the exception or error messages themselves, potential causes of these errors are often listed along with links to additional resources. To find the error you’re looking for, use your browser’s Find or Search capability and input a few words that you are seeing in your error message.

————– CANNOT RETRIEVE MAPPING FOR ACTION —————–
Cannot retrieve mapping for action Exception javax.servlet.jsp.JspException: Cannot retrieve mapping for action /Login Probable Cause No action defined in struts-config.xml to match that specified in the JSP’s Login.do”. Related Links

———— CANNOT RETRIEVE DEFINITION FOR FORM BEAN ———–
Cannot retrieve definition for form bean null Exception org.apache.jasper.JasperException: Cannot retrieve definition for form bean null Probable Cause This exception typically occurs because Struts cannot find the form bean it expects for a specific action according to the mapping in the struts-config.xml file. Most often, this is probably because the name given to the form in the name attribute of the form-bean element does not match the name attribute of the associated action’s action element. In other words, the action and form should each have a name attribute that matches exactly, including case. It has been reported that this error has been seen when no name attribute is associated with the action. If there is no name attribute in an action element, no form is associated with the action. Others have reported this error as merely a symptom of something completely unrelated (all too common), but the mismatch of name attributes in the form-bean and action elements in the struts-config.xml file is the usual culprit. ——- NO ACTION INSTANCE FOR PATH xxxxx COULD BE CREATED —— No action instance for path /xxxx could be created Exception No action instance for path /xxxx could be created Probable Causes Special Note: Because so many different things can cause this error, it is recommended that you turn your error logging/debugging levels on your web server to a high level of verbosity to see the underlying problems in trying to instantiate the action class you have written and associated with the specified action xxxx through an action mapping in the struts-config.xml file. Your Action class specified in the struts-config.xml file under the class attribute of the action mapping for action xxxx cannot be found for a variety of reasons, including (but not limited to): Failure to place compiled .class file for the action in the classpath (needs to be under WEB-INF/classes with the appropriate directory structure underneath this that matches the package your Action class belongs to). Package spelling or hierarchy specified in your action class itself (using the package keyword) does not match the spelling or complete package hierachy specified for your action class in the class attribute of the action in struts-config.xml. Action class specified in the /xxxx action mapping in the struts-config.xml file (class attribute) does not extend (directly or indirectly) from the Action class. In other words, your custom Action class does not extend off the Struts-provided Action class or off of another class that eventually extends the Action class (such as DispatchAction. Problem in your classpath, such as web server not being able to find ApplicationResources.properties files in the WEB-INF/classes/ directory or specified subdirectory. Problem in struts-config.xml file with action mapping. Problem with data-sources.xml file. Relevant Links Application’s Action classes does not extend Struts-provided Action class
Package hierarchy/directory structure specified in struts-config.xml file differs from that hierarchy specified in the actual action class’s file using the package keyword.
http://www.mail-archive.com/struts-user@jakarta.apache.org/msg65874.html Action Mapping mistake in struts-config.xml:
http://www.manning.com/ao/readforum.html?forum=siaao&readthread=177 data-sources.xml file?:
http://www.caucho.com/quercus/faq/section.xtp?section_id=30

————– NO GETTER METHOD FOR PROPERTY —————–
No getter method for property XXXX of bean org.apache.struts.taglib.html.BEAN Exception javax.servlet.jsp.JspException: No getter method for property username of bean org.apache.struts.taglib.html.BEAN Probable Causes No getXXXX() method defined for form field with name XXXX This can happen if the JSP/Struts developer forgets that the name of the get method will have the same spelling as the value supplied in the Struts tag’s property attribute, but that case will be different and is based on JavaBean specification rules. For example, my form class should have a getUsername method if my Struts form-related tag has username as the value for its property attribute. Note the difference in case marked with emphasis on the letter “U.” Related Links Case can trip up the matching between get method’s name and name specified in Struts tag
http://saloon.javaranch.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=58&t=000163

—————– NOCLASSDEFFOUNDERROR: ACTIONFORM —————– java.lang.NoClassDefFoundError: org/apache/struts/action/ActionForm Error java.lang.NoClassDefFoundError: org/apache/struts/action/ActionForm Probable Causes This error occurs typically when the specified Java .class file cannot be located in the classpath. If this occurs at runtime of a web application (error shows on browser rather than a rendered page), this typically means that specified class is not in the web server’s classpath (made up primarily of /WEB-INF/classes and /WEB-INF/lib contents). Note that the NoClassDefFoundError in general typically indicates lack of the specified class in the relevant classpath. In this particular case the missing class would be ActionForm.class This error is sometimes seen when one or more ActionForm.class instances are actually in the classpath. This most often occurs when ActionForm.class is made available correctly by placing struts.jar in the /WEB-INF/lib directory. When this library has been correctly placed and it is verified that ActionForm.class actually is present in the struts.jar file, the problem is either that more than one copy of ActionForm.class is in the classpath or (more likely) that duplicate versions of class files other than ActionForm are in the same classpath, causing confusion. This is especially true if a class that extends ActionForm is made available twice, such as in an .ear file that encompasses a .war file as well as in the .war file’s own classpath (/WEB-INF/classes). This problem can be resolved by guaranteeing that there are no redundant classes, especially those related to Struts (directly from Struts or extensions of Struts), in the web application’s view. Related Links EJB and Web Shared Links:
http://forum.java.sun.com/thread.jsp?forum=26&thread=413060&tstart=0&trange=15Keep Action and ActionForm (and their children) as non-overlapping unit(s) of an application

http://www.mail-archive.com/struts-user@jakarta.apache.org/msg47466.html

http://www.mail-archive.com/struts-user@jakarta.apache.org/msg47467.html

—————— CANNOT INSTANTIATE ACTIONFORM ———————
Exception creating bean of class org.apache.struts.action.ActionForm: {1} Exception javax.servlet.jsp.JspException: Exception creating bean of class org.apache.struts.action.ActionForm: {1} Probable Causes Instantiating Struts-provided ActionForm class directly instead of instantiating a class derived off ActionForm. This might occur implicitly if you specify that a form-bean is this Struts ActionForm class rather than specifying a child of this class for the form-bean. Not associating an ActionForm-descended class with an action can also lead to this error. Related Links

—– CANNOT FIND ACTIONMAPPINGS OR ACTIONFORMBEANS COLLECTION ——
Cannot find ActionMappings or ActionFormBeans collection Exception javax.servlet.jsp.JspException: Cannot find ActionMappings or ActionFormBeans collection Probable Causes Either the tags for the Struts action servlet or the tags for the .do extension mapping or both not present in the web.xml file. I saw a case where the web.xml file had no elements other than the root element and so this error was occurring. Typos or spelling errors in the struts-config.xml can lead to this error message. For example, missing a slash (“/”) on a closing tag can have this effect. Another element that must be present in the web.xml file is the load-on-startup element. This can be either an empty tag or can have an integer specified that indicates the priority of executing the associated servlet. The higher the number in the load-on-startup tags, the lower its priority. Another possibility, related to need to use load-on-startup tag, is that precompiling JSPs using Struts can lead to this message as well. Related Links Explicitly Define
http://saloon.javaranch.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=50&t=001055

http://threebit.net/tutorials/ejb/general/

———- NULLPOINTEREXCEPTION: REQUESTUTILS.FORWARDURL ———– NullPointerException at … RequestUtils.forwardURL Exception java.lang.NullPointerException at org.apache.struts.util.RequestUtils.forwardURL(RequestUtils.java:1223) Probable Causes Missing path attribute in the forward subelement of the action element in struts-config.xml Related Links

—————- CANNOT FIND BEAN IN ANY SCOPE —————–
Cannot find bean org.apache.struts.taglib.html.BEAN in any scope Exception javax.servlet.jsp.JspException: Cannot find bean org.apache.struts.taglib.html.BEAN in any scope Probable Causes Trying to use Struts form subelement tags outside of the Struts’ form tag. Note that this might be because you are using the Struts html tags after the closing tag. Note that if you accidentaly make your opening html:form tag a no-body tag (you put a closing / at the end so that it looks something like ), this may be treated by your web server’s parser as a no-body tag and everything after that tag you meant to be an opening tag will be outside of the form tag by default. Note your prefix may be different than html, but most people seem to use that as their prefix for the Struts HTML tags library. Related Links Using form subelements outside of a form tag
http://forum.java.sun.com/thread.jsp?thread=337537&forum=4&message=1384153

——————– MISSING MESSAGE FOR KEY ———————-
Missing message for key xx.xx.xx Exception javax.servlet.jsp.JspException: Missing message for key xx.xx.xx Probable Causes The key-value pair with specified key is not in ApplicationResources.properties file ApplicationResources.properties file not in classpath (not in WEB-INF/classes directory in specified location) Related Links

—————— CANNOT FIND MESSAGE RESOURCES ——————-
Cannot find message resources under key org.apache.struts.action.MESSAGE Exception Cannot find message resources under key org.apache.struts.action.MESSAGE Probable Causes Explicitly trying to use message resources that are not available (such as ApplicationResources.properties not available Implicitly trying to use message resources that are not available (such as using empty html:options tag instead of specifying the options in its body — this assumes options are specified in ApplicationResources.properties file) XML parser issues — too many, too few, incorrect/incompatible versions Related Links Provide Struts with Resource Bundle
http://threebit.net/tutorials/ejb/general/XML Parser Issues
http://www.mail-archive.com/struts-user@jakarta.apache.org/msg15779.html

————- NO INPUT ATTRIBUTE FOR MAPPING PATH —————
No input attribute for mapping path /loginAction Error No input attribute for mapping path /xxxxAction Probable Cause No input attribute in action mapping in struts-config.xml file for the action with the name specified in the error message. An input attribute is not required if form validation is not performed (either because the validate attribute is set to false or because the validation method in the relevant form class is not implemented. The input attribute specifies the page leading to this action because that page is used to display error messages from the form validation. Related Links

——————- STRANGE OUTPUT CHARACTERS ———————–
Strange Output Characters Error Strange and seemingly random characters in HTML and on screen, but not in original JSP or servlet. Probable Causes Regular HTML form tags intermixed incorrectly with Struts html:form tags. Encoding style used does not support characters used in page. Related Links

——————- DOCUMENT CONTAINED NO DATA ———————–
“Document contained no data” or no data rendered on page Error “Document contained no data” in Netscape No data rendered (completely empty) page in Microsoft Internet Explorer Probable Cause Employing a descendent of the Action class that does not implement the perform() method while using the Struts 1.0 libraries. Struts 1.1 Action child classes started using execute() rather than perform(), but is backwards compatible and supports the perform() method. However, if you write an Action-descended class for Struts 1.1 with an execute() method and try to run it in Struts 1.0, you will get this “Document contained no data” error message in Netscape or a completely empty (no HTML whatsoever) page rendered in Microsoft Internet Explorer.
Related Links

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Encoding in JBOSS – Request and Response

1. Find the server.xml in $JBOSS_HOME/server/$YOUR_SERVER/deployjbossweb-tomcat55.sar

2. Add URIEncoding=”UTF-8″

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<Connector port="8080" address="${jboss.bind.address}"

         maxThreads="250" maxHttpHeaderSize="8192"

         emptySessionPath="true" protocol="HTTP/1.1"

         enableLookups="false" redirectPort="8443" acceptCount="100"

         connectionTimeout="20000" disableUploadTimeout="true" URIEncoding="UTF-8"/>



   <!-- Define an AJP 1.3 Connector on port 8009 -->

    <Connector port="8009" address="${jboss.bind.address}" protocol="AJP/1.3"

         emptySessionPath="true" enableLookups="false" redirectPort="8443" URIEncoding="UTF-8"/>

3. Finished

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