Web Application Basics

HTTP - Hypertext Transfer (or Transport) Protocol), is a connectionless protocol for communicating clients/browsers and web servers

TCP/IP - Transmission Control Protocol, allows communication between your application software. It is responsible for breaking data down into IP packets before they are sent, and for assembling the packets when they arrive.
-connection oriented
-used to make connections and exchange information to one another
IP - Internet Protocol, is responsible for sending the packets to the correct destination
- connectionless

URL -Uniform Resource Locator, is a full specification of a resource. It includes the protocol, host machine name (domain name or IP address), optional protocol number and resource location.
Three ranges of port numbers:

1. well-known ports - from 0 through 1023
   20 & 21: File Transfer Protocol (FTP)
   22: Secure Shell (SSH)
   23: Telnet remote login service
   25: Simple Mail Transfer Protocol (SMTP)
   53: Domain Name System (DNS) service
   80: Hypertext Transfer Protocol (HTTP) used in the World Wide Web
   110: Post Office Protocol (POP3)
   119: Network News Transfer Protocol (NNTP)
   143: Internet Message Access Protocol (IMAP)
   161: Simple Network Management Protocol (SNMP)
   194: Internet Relay Chat (IRC)
   443: HTTP Secure (HTTPS)
   465: SMTP Secure (SMTPS)
2. the registered ports - from 1024 through 49151
   - they can be registered to specific protocols by software corporations/companies or users
   - assigned by or registered to Internet Assigned Numbers Authority (IANA) (or by Internet Corporation for Assigned Names and Numbers (ICANN) before March 21, 2001[1])
3. dynamic or private ports - from 49152 through 65535
   - available for use by any application or just about anybody

HTML - is the principal language b/w the client and server that expresses content of webpages.

• DOM - is an interface to the browser and HTML/XML documents.


• DHTML
  Dynamic HTML is a term used to describe the combination of HTML, style sheets, and scripts that allow dynamic pages.


• Javascript - is the most common scripting language for browsers.


• Inversion of Control and Dependency Injection

Martin Fowler, who first coined Dependency Injection, considers it the same to Inversion of Control. He used Dependency Injection since he finds Inversion of Control too generic. However, other sources claim that Dependency Injection is just a form of Inversion of Control. With all the articles and blogs written about them, it is very easy to get confused. So I'll try to summarize their description here according to my own understanding and hopefully, it will be simple and easy to understand.

Inversion of Control is a general principle in which the flow of control is inverted, unlike the traditional sequential flow. It follows the "Hollywood principle" - "don't call us, we'll call you". Your objects don't call services directly. Instead, your objects expect to be called. It is the framework that manages the objects and services, and is aware of what to instantiate and invoke.

The main idea of Inversion of Control is to have none of your classes know or care how they get the objects they depend on.

Dependency Injection is a way of implementing Inversion of Control in which an external mechanism is supplied in order for your objects not to call services (other objects) directly and therefore not depend on them. The external mechanism is the one responsible in injecting the concrete implementation that your objects needed.


• Loose coupling - describes a relationship of two entities/objects where they can interact, but have very little knowledge of each other.

To r: inline css vs external css

What is robustness?

Disadvan of frames

Website-static

Webapp-dynamic

Get vs post- when to use get?

Session - uses cookies

Enabling technoligies:

Compiled modules-java servlets

Interpreted scripts-jsp

Other Pointers

• Weblogic Erroneous Handlers Error - this is caused by the jrockit version of jdk. To get the correct error message, use the Java jdk first. Source: http://ricksolutions.blogspot.hk/2009/03/fixing-erroneous-handlers-error.html
• checking tables on db2
select * from sysibm.systables where dbname='NACS01DB' and name like 'PC%'
• command for unzipping war files
jar xvf xxx.war
• Extracting the Contents a JAR File
  The basic command to use for extracting the contents of a JAR file is:
  

  jar xf jar-file [archived-file(s)] 

  Let's look at the options and arguments in this command:
  
  • The x option indicates that you want to extract files from the JAR archive.
  • The f options indicates that the JAR file from which files are to be extracted is specified on the command line, rather than through stdin.
  • The jar-file argument is the filename (or path and filename) of the JAR file from which to extract files.
  • archived-file(s) is an optional argument consisting of a space-delimited list of the files to be extracted from the archive. If this argument is not present, the Jar tool will extract all the files in the archive.
• character encoding - http://www.joelonsoftware.com/articles/Unicode.html
• DB2 Timestamp to java.util.Date or java.sql.Timestamp
  
  • DB2 format = yyyy-MM-dd HH:mm:ss.ZZZZZZ where Z = seconds since previos midnight (00000 - 86400), http://pic.dhe.ibm.com/infocenter/db2luw/v9r7/index.jsp?topic=%2Fcom.ibm.db2.luw.sql.ref.doc%2Fdoc%2Fr0007107.html
  • java.sql.Timestamp = yyyy-mm-dd hh:mm:ss.fffffffff where f = nanoseconds
  The ZZZZZZ part of DB2 timestamp is insignificant because it is just the total seconds since previos midnight.
  To convert to java.util.Date, use
  

  new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse(dateStr)

  To convert to java.sql.Timestamp, use
  

  resultSet.getTimestamp([column name or column index])

• 
  

Ref:
http://technobuz.com/2011/04/run-commands-for-microsoft-applications/

Java Pointers / Links

• strength and limitations of for each loop (for( : ))
  http://today.java.net/article/2006/11/03/nuances-java-50-each-loop


• Loading properties/configurationfiles


• Java 5 New Features
  http://java.sun.com/j2se/1.5.0/docs/relnotes/features.html
  http://java.sun.com/developer/technicalArticles/releases/j2se15/
  http://download.oracle.com/javase/1.5.0/docs/guide/language/index.html


• Increase Java Performance
  http://java.sun.com/developer/technicalArticles/Programming/Performance/


• Java Language Best Practices
  http://docs.oracle.com/cd/A97688_16/generic.903/bp/java.htm


• Code Conventions for the Java Programming Language
  http://www.oracle.com/technetwork/java/codeconv-138413.html


• ThreadLocal - http://java.dzone.com/articles/java-thread-local-%E2%80%93-how-use


• String Concatenation
  - use plus operator(+) only if all operands are constants
  

      1) String temp = “alpha” + “beta”;
           '-> String temp = “alphabeta”; (compile time translation)
      2) String temp = x + “beta”;
           '-> String temp = (new StringBuilder()).append(x).append(“beta”).toString();

  - concat using plus operator uses StringBuilder and String behind the scenes:

      “alpha” + “beta” = new StringBuilder(String.toString(“alpha”)).append(“beta”).toString()

  - use String.concat if concatenating only 2 or few strings
  - use StringBuilder(unsynchronized)/StringBuffer(synchronized) for more than 2 strings, specially in a loop
  - in a loop, SB is better than concat is better than +
  - always initialize SB with initial capacity to greatly improve performance
  

  new SB() has 16 char initial capacity by default

  
  - best explanation is here: http://www.znetdevelopment.com/blogs/2009/04/06/java-string-concatenation/


• character set conversion

String stringToConvert = bmText;
byte[] convertStringToByte = stringToConvert.getBytes("UTF-8");
bmText = new String(convertStringToByte, "ISO-8859-1");
options.add(new SelectOption(bmValue, new String(bmText)));



• creating pdf
-header w/ image


  public void doHeader() throws Exception {
      Image logoImage = PDFUO.getLogoImage();
      //logoImage.setAbsolutePosition(ReportConstantsIF.ITEXT_POINTS/2, length - ReportConstantsIF.ITEXT_POINTS);
      logoImage.setAlignment(Image.ALIGN_TOP | Image.TEXTWRAP);
    
      Paragraph p = new Paragraph();
      p.add(logoImage);
      p.add(new Phrase("BEAR, STEARNS SECURITIES CORP." + "\n\n", new Font(Font.TIMES_ROMAN, 6, Font.BOLD)));
p.add(new Phrase(
        "ONE METROTECH CENTER NORTH" + "\n" +
  "BROOKLYN, NEW YORK 11201-3859" + "\n" +
  "(212) 272-1000", smallFont));
      p.setLeading(9f);
    
      HeaderFooter header = new HeaderFooter(p, false);
      header.setAlignment(Element.ALIGN_RIGHT);
      header.setBorder(PdfTable.NO_BORDER);

      document.setHeader(header);
  }


-error occurs and data is not displayed when the columns in a row is not complete in PdfPTable

JSP Pointers

• secure/nonsecure alerts on IE6 & 7
http://www.zorked.com/security/ie-mixed-content-secure-nonsecure-items/


• no caching on browsers
add: (remove space b/w < and META)

  
< META HTTP-EQUIV="Expires" CONTENT="0"> - any # less than 1 means no cache
< META HTTP-EQUIV="Pragma" CONTENT="no-cache"> - for backward compatability
< META HTTP-EQUIV="Cache-Control" CONTENT="no-cache"> - for HTTP 1.1 spec  



• day in Date

function fnGetPrevDayDate(objDate){
 // 1 day = 86400000 ms 
 // var datPrevDate = new Date(objDate.getTime() - 86400000);
 // code above returns incorrect result when time changes from DST to standard time
 
 var datPrevDate = new Date(objDate);
 datPrevDate.setDate(datPrevDate.getDate() - 1);
 return datPrevDate;
}



• html:checkbox
-If the form is in session and you change the checkbox from true(checked) to false(unchecked), the checkbox attribute in form is not set back to false. This is because the unchecked checkbox is not sent in the request and is therefore not set in the form.
-solution: Add a reset method in form & reset checkbox to false. Everytime you submit the form, form is reset and then populated before moving to action, thus having correct value for the checkbox.


• how to use indexId on logic:iterate

< logic:iterate id="entityRow" name="<%= DerivativeEntityConstantsIF.SEARCH_RESULT %>" scope="session" offset="<%= String.valueOf(offset)%>" length="<%= String.valueOf(maxLength)%>" indexId="indexNum">
  < html:select name="entityRow" property="linkageClassCode"
onchange='<%= "fnEditValue(this, " + indexNum + ")" %>' >...



• html element default values - defaultValue/defaultSelectedd

if (frm["termDeal.accountNo"].value != frm["termDeal.accountNo"].defaultValue) return true;
if (fnIsSelectChanged(frm["termDeal.currency"])) return true;

function fnIsSelectChanged(selectObj) {
  var index = selectObj.selectedIndex;
  var selectedOption = selectObj.options[index];
  if (selectedOption.defaultSelected) return false; 
  return true;
}



• use popUpCalendar.js

if (!document.layers){
var startDate = document.getElementById("personalInfoForm.dateOfBirth");
// use showCalendarWithHolidays if you want to show holidays
document.write("<[toRemove]a href='javascript:void(0)' onclick='showCalendarWithHolidays(this, startDate, \"mm-dd-yyyy\",null,1,-1,-1, true)'><[toRemove]img src='' border='0'/>");
}



• regex of replace

.value.replace(/_|-/g, '')  --> replace _ and - with empty str



• use of sessionScope

CL.isNewClient = ${sessionScope[ClientConstants.IS_NEW_CLIENT]} --> do not put semi colon at end (not sure if for AMS only)

Deep copy of Java objects

The class Object's clone method only performs a shallow copy. This means that it creates a new instance of the object but the fields of both the new and original object end up referencing the same objects because only the reference of the fields is copied to the new object. To make deep copies of an object, we can use this class:

import java.io.IOException;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;

/**
 * Utility for making deep copies (vs. clone()'s shallow copies) of
 * objects. Objects are first serialized and then deserialized. Error
 * checking is fairly minimal in this implementation. If an object is
 * encountered that cannot be serialized (or that references an object
 * that cannot be serialized) an error is printed to System.err and
 * null is returned. Depending on your specific application, it might
 * make more sense to have copy(...) re-throw the exception.
 *
 * A later version of this class includes some minor optimizations.
 */
public class ObjectCloner {

    // so that nobody can accidentally create an ObjectCloner object
    private ObjectCloner() {
    }

    /**
     * Returns a copy of the object, or null if the object cannot
     * be serialized.
     */
    public static Object deepCopy(Object orig) {
        Object obj = null;
        try {
            // Write the object out to a byte array
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            ObjectOutputStream out = new ObjectOutputStream(bos);
            out.writeObject(orig);
            out.flush();
            out.close();

            // Make an input stream from the byte array and read
            // a copy of the object back in.
            ObjectInputStream in = new ObjectInputStream(
                new ByteArrayInputStream(bos.toByteArray()));
            obj = in.readObject();
        }
        catch(IOException e) {
            e.printStackTrace();
        }
        catch(ClassNotFoundException cnfe) {
            cnfe.printStackTrace();
        }
        return obj;
    }
}

Sample call: Object clone = ObjectCloner.deepCopy(oldObject);
A more optimized version can be found here: http://javatechniques.com/blog/faster-deep-copies-of-java-objects/

NYAOS (NYACUS,NYADOS,NYAOS-II)

- Nihongo Yet Another Open Shell
- an enhanced commandline shell for Windows,DOS,OS/2
- advantages include filename autocomplete, built-in color, history, etc.
- support and downloads: http://nyaos.org/


1) Download and unzip
2) create env.bat with:
set MAVEN_HOME=S:\commons\apache-maven-2.0.10
set ANT_HOME=S:\commons\apache-ant-1.7.0
set JAVA_HOME=R:\commons\bea\jrockit_150_15
set path=%JAVA_HOME%\bin\;%MAVEN_HOME%\bin;%ANT_HOME%\bin;%PATH%;S:\commons\scripts;D:\Program Files\Rational\clearcase\ClearCase\bin;s:\commons\firefox
mvn -version
3) use nyacus as your cmd with the env properties by creating mycmd.bat with:
nyacus -r env.bat (means that you are loading the script file env.bat instead of _nya)
4) can start other apps by creating start command like eclipse.bat:
set path=R:\commons\bea\jrockit_150_15\bin\;%PATH%;
cmd /C start R:\commons\eclipse -data R:\bel\workspace\workspace33 -vmargs -Xms40m -Xmx512m -XX:MaxPermSize=256m
5) launch mycmd.bat
6) start other apps by calling filename of .cmd

Understanding Web Service

Web Service

- a software system designed to support interoperable machine-to-machine interaction over a network.
- makes software functionality available over the Internet so that programs like PHP, ASP, JSP, JavaBeans, the COM object, and all our other favorite widgets can make a request to a program running on another server (a web service) and use that program’s response in a website, WAP service, or other application.
- describes a standardized way of integrating Web-based applications using the XML, SOAP, WSDL and UDDI open standards over an Internet protocol backbone.

2 Types of Web Service

1. SOAP (Simple Object Access Protocol)
   - a lightweight XML-based messaging protocol used to encode the information in Web service request and response messages before sending them over a network.
   - SOAP messages are formatted in XML and are typically sent using HTTP but can be also transported using a variety of Internet protocols, including SMTP and MIME.
   - older type, successor of XML-RPC
   - uses JAX-WS specification
2. REST
   - is simpler and more light weighted than SOAP
   - can send and receive data as JSON, XML or even plain text
   - uses JAX-RS specification

Related Terms

XML (Extensible Markup Language)
- a general-purpose specification for creating custom markup languages developed by the W3C.
- is a markup language much like HTML. A markup language is a mechanism to identify structures in a document.
- allows designers to create their own customized tags, enabling the definition, transmission, validation, and interpretation of data between applications and between organizations.

WSDL (Web Services Description Language)
- an XML-formatted language used to describe a Web service's capabilities as collections of communication endpoints capable of exchanging messages. WSDL is the language that UDDI uses, developed jointly by Microsoft and IBM.
- describes the interface of Web services

UDDI (Universal Description, Discovery and Integration)
- it is a Web-based distributed directory that enables businesses to list themselves on the Internet and discover each other, similar to a traditional phone book's yellow and white pages.

SEI (Service Endpoint Interface)
- is a Java interface class that defines the methods to be exposed as a Web service
- coverts the web service call including the (Java, C++, etc.) objects to a SOAP message

Protocol
- is a convention or standard that controls or enables the connection, communication, and data transfer between two computing endpoints. In its simplest form, a protocol can be defined as the rules governing the syntax, semantics, and synchronization of communication. Protocols may be implemented by hardware, software, or a combination of the two.

References:
http://www.alistapart.com/articles/webservices
http://en.wikipedia.org
http://www.webopedia.com/TERM/W/Web_services.html
http://www.webopedia.com/DidYouKnow/Computer_Science/2005/web_services.asp
http://www.ibm.com/developerworks/library/ws-intwsdl
http://www.ibm.com/developerworks/library/ws-intwsdl2