In this chapter, we will discuss how to handle data in JSP. One of the most important advantages of using JSP is that you can use all the methods available in core Java. We will take you through the Date class which is available in the java.util package; this class encapsulates the current date and time.
The Date class supports two constructors. The first constructor initializes the object with the current date and time.
The following constructor accepts one argument that equals the number of milliseconds that have elapsed since midnight, January 1, 1970.
Once you have a Date object available, you can call any of the following support methods to play with dates −
|S.No.||Methods & Description|
boolean after(Date date)
Returns true if the invoking Date object contains a date that is later than the one specified by date, otherwise, it returns false.
boolean before(Date date)
Returns true if the invoking Date object contains a date that is earlier than the one specified by date, otherwise, it returns false.
Object clone( )
Duplicates the invoking Date object.
int compareTo(Date date)
Compares the value of the invoking object with that of date. Returns 0 if the values are equal. Returns a negative value if the invoking object is earlier than date. Returns a positive value if the invoking object is later than date.
int compareTo(Object obj)
Operates identically to compareTo(Date) if obj is of class Date. Otherwise, it throws a ClassCastException.
boolean equals(Object date)
Returns true if the invoking Date object contains the same time and date as the one specified by date, otherwise, it returns false.
long getTime( )
Returns the number of milliseconds that have elapsed since January 1, 1970.
int hashCode( )
Returns a hash code for the invoking object.
void setTime(long time)
Sets the time and date as specified by time, which represents an elapsed time in milliseconds from midnight, January 1, 1970
String toString( )
Converts the invoking Date object into a string and returns the result.
With JSP program, it is very easy to get the current date and the time. You can use a simple Date object with the toString() method to print the current date and the time as follows −
<%@ page import = "java.io.*,java.util.*, javax.servlet.*" %> <html> <head> <title>Display Current Date & Time</title> </head> <body> <center> <h1>Display Current Date & Time</h1> </center> <% Date date = new Date(); out.print( "<h2 align = \"center\">" +date.toString()+"</h2>"); %> </body> </html>
Let us now keep the code in CurrentDate.jsp and then call this JSP using the URL http://localhost:8080/CurrentDate.jsp. You will receive the following result −
Display Current Date & Time
Mon Jun 21 21:46:49 GMT+04:00 2010
Refresh the page with the URL http://localhost:8080/CurrentDate.jsp. You will find difference in seconds everytime you would refresh.
As discussed in the previous sections, you can use all the available Java methods in your JSP scripts. In case you need to compare two dates, consider the following methods −
You can use getTime( ) method to obtain the number of milliseconds that have elapsed since midnight, January 1, 1970, for both objects and then compare these two values.
You can use the methods before( ), after( ), and equals( ) because the 12th of the month comes before the 18th; for example, new Date(99, 2, 12).before(new Date (99, 2, 18)) returns true.
You can use the compareTo( ) method; this method is defined by the Comparable interface and implemented by Date.
SimpleDateFormat is a concrete class for formatting and parsing dates in a locale-sensitive manner. SimpleDateFormat allows you to start by choosing any user-defined patterns for date-time formatting.
Let us modify the above example as follows −
<%@ page import = "java.io.*,java.util.*" %> <%@ page import = "javax.servlet.*,java.text.*" %> <html> <head> <title>Display Current Date & Time</title> </head> <body> <center> <h1>Display Current Date & Time</h1> </center> <% Date dNow = new Date( ); SimpleDateFormat ft = new SimpleDateFormat ("E yyyy.MM.dd 'at' hh:mm:ss a zzz"); out.print( "<h2 align=\"center\">" + ft.format(dNow) + "</h2>"); %> </body> </html>
Compile the above servlet once again and then call this servlet using the URL http://localhost:8080/CurrentDate. You will receive the following result −
Display Current Date & Time
Mon 2010.06.21 at 10:06:44 PM GMT+04:00
To specify the time format, use a time pattern string. In this pattern, all ASCII letters are reserved as pattern letters, which are defined as the following −
|y||Year in four digits||2001|
|M||Month in year||July or 07|
|d||Day in month||0|
|h||Hour in A.M./P.M. (1~12)||2|
|H||Hour in day (0~23)||22|
|m||Minute in hour||30|
|s||Second in minute||55|
|E||Day in week||Tuesday|
|D||Day in year||360|
|F||Day of week in month||2 (second Wed. in July)|
|w||Week in year||40|
|W||Week in month|
|k||Hour in day (1~24)||24|
|K||Hour in A.M./P.M. (0~11)||0|
|z||Time zone||Eastern Standard Time|
|'||Escape for text||Delimiter|
For a complete list of constant available methods to manipulate date, you can refer to the standard Java documentation.