Servlet processing date

One of the most important advantages of using Servlets is that you can use most of the methods available in core Java. This chapter will explain the Date class in the java.util package provided by Java. This class encapsulates the current date and time.

The Date class supports two constructors. The first constructor initializes an object with the current date and time.

Date( )

The following constructor accepts a parameter equal to the number of milliseconds that have elapsed since midnight on January 1, 1970.

Date(long millisec)

Once you have a available Date object, you can call any of the following supported methods to use the date:

Serial number	Method & Description
1	boolean after(Date date) If the date contained in the called Date object is specified by date After the date, it returns true, otherwise it returns false.
2	boolean before(Date date) If the date contained in the called Date object is before the date specified by date, It returns true, otherwise it returns false.
3	Object clone( ) Repeatedly call the Date object.
4	int compareTo(Date date) Compare the value of the calling object with the value of date. If the two values are equal, 0 is returned. If the calling object precedes date, a negative value is returned. If the calling object comes after date, a positive value is returned.
5	int compareTo(Object obj) If obj is a Date class, the operation is equivalent to compareTo(Date). Otherwise, it throws a ClassCastException.
6	boolean equals(Object date) If the time and date contained in the called Date object are the same as those specified by date , returns true, otherwise returns false.
7	long getTime( ) Returns the number of milliseconds that have elapsed since January 1, 1970.
8	int hashCode( ) Returns the hash code for the calling object.
9	void setTime(long time) Set time to the specified time and date, which means since January 1, 1970 The elapsed time in milliseconds since midnight of the day.
10	String toString( ) Convert the called Date object to a string and return the result.

Get the current date and time

Getting the current date and time in Java Servlet is very easy. You can use the toString() method of a simple Date object to output the current date and time, as shown below:

// 导入必需的 java 库
import java.io.*;
import java.util.Date;
import javax.servlet.*;
import javax.servlet.http.*;
 
// 扩展 HttpServlet 类
public class CurrentDate extends HttpServlet {
 
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
            throws ServletException, IOException
  {
      // 设置响应内容类型
      response.setContentType("text/html");
 
      PrintWriter out = response.getWriter();
      String title = "显示当前的日期和时间";
      Date date = new Date();
      String docType =
      "<!doctype html public \"-//w3c//dtd html 4.0 " +
      "transitional//en\">\n";
      out.println(docType +
        "<html>\n" +
        "<head><title>" + title + "</title></head>\n" +
        "<body bgcolor=\"#f0f0f0\">\n" +
        "<h1 align=\"center\">" + title + "</h1>\n" +
        "<h2 align=\"center\">" + date.toString() + "</h2>\n" +
        "</body></html>");
  }
}

Now, let us compile the above Servlet and run Create the appropriate entries in the web.xml file and then call the servlet by accessing http://localhost:8080/CurrentDate. This will produce the following result:

Display the current date and time

Mon Jun 21 21:46:49 GMT+04: 00 2010

Try refreshing the URL http://localhost:8080/CurrentDate, you will notice the difference in the displayed time every few seconds.

Date Comparison

As mentioned above, you can use all available Java methods in Servlet. If you need to compare two dates, here's how:

You can use getTime() to get the elapsed time (in milliseconds) since midnight on January 1, 1970 for both objects unit) and then compare the two values.
You can use the methods before( ), after( ) and equals( ). Since the 12th is before the 18th in a month, for example, new Date(99, 2, 12).before(new Date (99, 2, 18)) returns true.
You can use the compareTo( ) method, which is defined by the Comparable interface and implemented by Date.

Formatting dates using SimpleDateFormat

SimpleDateFormat is a concrete class for formatting and parsing dates in a locale-sensitive manner. SimpleDateFormat allows you to choose any user-defined date-time formatting mode.

Let us modify the above example as follows:

// 导入必需的 java 库
import java.io.*;
import java.text.*;
import java.util.Date;
import javax.servlet.*;
import javax.servlet.http.*;
 
// 扩展 HttpServlet 类
public class CurrentDate extends HttpServlet {
 
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
            throws ServletException, IOException
  {
      // 设置响应内容类型
      response.setContentType("text/html");
 
      PrintWriter out = response.getWriter();
      String title = "显示当前的日期和时间";
      Date dNow = new Date( );
      SimpleDateFormat ft = 
      new SimpleDateFormat ("E yyyy.MM.dd 'at' hh:mm:ss a zzz");
      String docType =
      "<!doctype html public \"-//w3c//dtd html 4.0 " +
      "transitional//en\">\n";
      out.println(docType +
        "<html>\n" +
        "<head><title>" + title + "</title></head>\n" +
        "<body bgcolor=\"#f0f0f0\">\n" +
        "<h1 align=\"center\">" + title + "</h1>\n" +
        "<h2 align=\"center\">" + ft.format(dNow) + "</h2>\n" +
        "</body></html>");
  }
}

Compile the above Servlet again, and then call the Servlet by accessing http://localhost:8080/CurrentDate. This will produce the following result:

Display the current date and time

Mon 2010.06.21 at 10:06:44 PM GMT +04:00

Format codes for simple date formats

Use event pattern strings to specify the time format. In this mode, all ASCII letters are reserved as mode letters, which are defined as follows:

##hWith A.M./P.M. The hour (1~12)12HThe hour of the day (0~23) 22##msSE##DDay of the year# The week is the first week of this monthWeek of the year Week of JanuaryA.M./P.M. MarkingThe hour of the day (1~24) with Hours with A.M./P.M. (0~11) Time zoneEscape for textSingle quoteFor a complete list of available methods for working with dates, you can refer to the standard Java documentation .

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Character	Description	Example
G	Era indicator	AD
y	four digits The year represented by the number	2001
M	The month in the year	July or 07
d	Days of January	10


What minute of the hour	30
The number of seconds in a minute	55
Milliseconds	234
Day of the week	Tuesday
##360		F
2 (second Wed. in July)		w
40		W
1		a
PM		k
24		K
10		z
Eastern Standard Time		'
Delimiter		"
`