How do I decompress a zip file using ZipInputStream?

By Wayan in Zip and GZIP 0 Comment

The code below shows how to decompress and extract files from a zip archive. In the example we use the java.util.zip.ZipInputStream class.

package org.kodejava.util.zip;

import java.io.*;
import java.util.zip.ZipInputStream;
import java.util.zip.ZipEntry;

public class UnzipDemo {
    public static void main(String[] args) {
        String zipName = "data.zip";

        try (FileInputStream fis = new FileInputStream(zipName);
             ZipInputStream zis =
                 new ZipInputStream(new BufferedInputStream(fis))) {

            ZipEntry entry;

            // Read each entry from the ZipInputStream until no
            // more entry found indicated by a null return value
            // of the getNextEntry() method.
            while ((entry = zis.getNextEntry()) != null) {
                System.out.println("Unzipping: " + entry.getName());

                int size;
                byte[] buffer = new byte[2048];

                try (FileOutputStream fos =
                         new FileOutputStream(entry.getName());
                     BufferedOutputStream bos =
                         new BufferedOutputStream(fos, buffer.length)) {

                    while ((size = zis.read(buffer, 0, buffer.length)) != -1) {
                        bos.write(buffer, 0, size);
                    }
                    bos.flush();
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I check if a string is a valid date?

By Wayan in Core API, Text Package 1 Comment

The following code can be used to validate if a string contains a valid date information. The pattern of the date is defined by the java.text.SimpleDateFormat object. When the date is not valid a java.text.ParseException will be thrown.

package org.kodejava.text;

import java.text.SimpleDateFormat;
import java.text.ParseException;

public class DateValidation {
    public static void main(String[] args) {
        SimpleDateFormat format = new SimpleDateFormat("dd/MM/yyyy");

        // Input to be parsed should strictly follow the defined date format
        // above.
        format.setLenient(false);

        String date = "29/18/2021";
        try {
            format.parse(date);
        } catch (ParseException e) {
            System.out.println("Date " + date + " is not valid according to " +
                    format.toPattern() + " pattern.");
        }
    }
}

The result of the above date validation code is:

Date 29/18/2021 is not valid according to dd/MM/yyyy pattern.

How do I get Java Home directory?

By Wayan in Core API, Lang Package 0 Comment

To get Java Home directory we can obtain it from system properties using the java.home key.

package org.kodejava.lang;

public class JavaHomeDirectory {
    public static void main(String[] args) {
        String javaHome = System.getProperty("java.home");
        System.out.println("JAVA HOME = " + javaHome);
    }
}

On my computer this code give me the following output:

JAVA HOME = C:\Program Files\Java\jdk-17

How do I get the username of operating system active user?

By Wayan in Core API, Lang Package 0 Comment

This example show you how to get operating system active user’s login name. We can obtain the username of current user by reading system properties using the user.name key.

package org.kodejava.lang;

public class GettingUserName {
    public static void main(String[] args) {
        String username = System.getProperty("user.name");
        System.out.println("username = " + username);
    }
}

How do I get web application context path in JSP?

By Wayan in JSP 2 Comments

This example show you how to obtain web application context path in JSP using Expression Language (EL) feature of JSP. To get the context path we can utilize the pageContext, it is an implicit object that available on every JSP pages. From this object you can get access to various object such as:

  • servletContext
  • session
  • request
  • response

To get the context path value you will need to read it from the request.contextPath object. This contextPath can be useful for constructing a path to you web resources such as CSS, JavaScript and images. Libraries that you’ll need to enable the JSP Expression Language (EL) in your JSP Pages, which usually already included in a Servlet container such as Apache Tomcat.

Here is our context-path.jsp file.

<%@ page contentType="text/html;charset=UTF-8" %>
<!DOCTYPE html>
<html lang="en">
<head>
    <title>JSP - Context Path</title>
</head>

<body>
Web Application Context Path = ${pageContext.request.contextPath}
</body>
</html>

Maven dependencies

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
</dependency>

Maven Central