Kode Java - Learn Java by Examples

How do I create a servlet filter to make secure cookies?

By Wayan in Servlet Last modified: April 18, 2024 0 Comment

The CookieFilter class in this example is a servlet filter. Servlet filters in Java web applications are used to perform tasks such as request/response modification, authentication, logging, and more. In the context of managing cookies, a CookieFilter can be used to intercept requests and responses to handle cookie-related operations, such as setting secure attributes on cookies or checking cookie values for authentication purposes.

Here’s an example of how you can implement a CookieFilter class in Java:

package org.kodejava.filter;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebFilter("/*")
public class CookieFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // Initialization code, if needed
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) 
            throws IOException, ServletException {
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        HttpServletResponse httpResponse = (HttpServletResponse) response;

        // Check if a session exists
        HttpSession session = httpRequest.getSession(false);
        if (session != null) {
            // Example: Set secure attribute on session cookie
            sessionCookieSecure(httpRequest, httpResponse);
        }

        // Continue the request chain
        chain.doFilter(request, response);
    }

    @Override
    public void destroy() {
        // Cleanup code, if needed
    }

    private void sessionCookieSecure(HttpServletRequest request, HttpServletResponse response) {
        // Assuming the session cookie name
        String cookieName = "JSESSIONID"; 
        Cookie[] cookies = request.getCookies();
        if (cookies != null) {
            for (Cookie cookie : cookies) {
                if (cookie.getName().equals(cookieName)) {
                    // Set the secure attribute on the session cookie
                    cookie.setSecure(true);
                    // Update the cookie in the response
                    response.addCookie(cookie); 
                    break;
                }
            }
        }
    }
}

In this example:

The CookieFilter class implements the Filter interface, which requires implementing methods like init, doFilter, and destroy.
Inside the doFilter method, it checks if a session exists for the incoming request.
If a session exists, it calls the sessionCookieSecure method to set the secure attribute on the session cookie.
The sessionCookieSecure method iterates through cookies in the request, finds the session cookie (e.g., JSESSIONID), and sets its secure attribute to true.

You can modify this filter implementation based on your specific cookie management requirements, such as setting secure attributes on specific cookies or performing additional cookie-related tasks.

How do I configure secure cookies using web.xml?

By Wayan in Servlet Last modified: April 18, 2024 0 Comment

To configure secure cookies using web.xml, you typically need to set the secure attribute on your cookie definitions. This ensures that the cookie is only sent over HTTPS connections, enhancing security by protecting sensitive information from being transmitted over unencrypted channels. Here’s how you can do it:

1. Define Your Servlet Filter (Optional but Recommended):

If you don’t have a servlet filter for managing cookies, you can create one. This filter can intercept requests and responses to handle cookie-related operations.

<filter>
    <filter-name>CookieFilter</filter-name>
    <filter-class>org.kodejava.servlet.CookieFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>CookieFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

Replace org.kodejava.servlet.CookieFilter with the actual class that implements your cookie handling logic.

2. Configure Secure Cookie in web.xml:

Inside your web.xml, you can define cookie configurations using <session-config> and <cookie-config> elements.

<session-config>
   <cookie-config>
      <!-- Recommended to prevent client-side script access -->
      <http-only>true</http-only>
      <!-- Set all cookies to be secure -->
      <secure>true</secure>
    </cookie-config>
</session-config>

<secure>true</secure>: This line ensures that all cookies are marked as secure, meaning they will only be sent over HTTPS connections.
<http-only>true</http-only>: This line makes cookies accessible only through HTTP headers, preventing client-side scripts (like JavaScript) from accessing them. It adds another layer of security against certain types of attacks.

3. Deploy and Test:

After making these changes, deploy your web application and test it over HTTPS. Verify that cookies are being set with the secure flag by checking your browser’s developer tools (usually under the “Application” or “Storage” tab).

By following these steps, you can configure secure cookies in your Java web application using web.xml.

Notes: Setting the secure attribute in web.xml configures the default behavior for cookies created by the servlet container. However, for custom cookies that your application creates programmatically, you need to explicitly call setSecure(true) on the Cookie object to make them secure.

How do I create a table with multiple header in iText 8?

By Wayan in iText PDF Last modified: March 16, 2024 0 Comment

In the following example we are going to create a table with multiple header. We will create table header with columns that spans in multiple columns and rows.

Here are the steps:

Create a PdfWriter object called writer with the output filename.
Create a PpdfDocument object called pdf, and pass the writer object as parameter.
Using try-with-resource block, create a Document object with the pdf object as constructor argument.
Instantiate a Table object. In this example we define it with five columns, and set the width of the table to take the full page width.
Add table header cell using addHeaderCell() method. We add cell that spans multiple rows or multiple columns using the Cell constructor parameters rowspan and colspan.
Add some rows of data to the table.
Finally, we add the table object to the document.

And here is the full code snippet:

package org.kodejava.itext;

import com.itextpdf.kernel.pdf.PdfDocument;
import com.itextpdf.kernel.pdf.PdfWriter;
import com.itextpdf.layout.Document;
import com.itextpdf.layout.element.Cell;
import com.itextpdf.layout.element.Paragraph;
import com.itextpdf.layout.element.Table;
import com.itextpdf.layout.properties.TextAlignment;
import com.itextpdf.layout.properties.UnitValue;
import com.itextpdf.layout.properties.VerticalAlignment;

import java.io.FileNotFoundException;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

public class TableWithMultiHeader {
    public static void main(String[] args) {
        TableWithMultiHeader demo = new TableWithMultiHeader();
        demo.createTable();
    }

    private void createTable() {
        try {
            PdfWriter writer = new PdfWriter("multi_header_table.pdf");
            PdfDocument pdf = new PdfDocument(writer);

            try (Document document = new Document(pdf)) {
                Table table = new Table(5);
                table.setWidth(UnitValue.createPercentValue(100));

                table.addHeaderCell(new Cell(2, 1)
                        .setVerticalAlignment(VerticalAlignment.MIDDLE)
                        .setTextAlignment(TextAlignment.CENTER)
                        .add(new Paragraph("No")));
                table.addHeaderCell(new Cell(2, 1)
                        .setVerticalAlignment(VerticalAlignment.MIDDLE)
                        .setTextAlignment(TextAlignment.CENTER)
                        .add(new Paragraph("Name")));
                table.addHeaderCell(new Cell(1, 2)
                        .setTextAlignment(TextAlignment.CENTER)
                        .add(new Paragraph("Date: " + LocalDate.now()
                                .format(DateTimeFormatter.ofPattern("dd-MMM-yyyy")))));
                table.addHeaderCell(new Cell(2, 1)
                        .setVerticalAlignment(VerticalAlignment.MIDDLE)
                        .setTextAlignment(TextAlignment.CENTER)
                        .add(new Paragraph("Activity")));
                table.addHeaderCell(new Cell(1, 1)
                        .setTextAlignment(TextAlignment.CENTER)
                        .add(new Paragraph("Start Time")));
                table.addHeaderCell(new Cell(1, 1)
                        .setTextAlignment(TextAlignment.CENTER)
                        .add(new Paragraph("End Time")));

                table.addCell(new Cell()
                        .setTextAlignment(TextAlignment.RIGHT)
                        .add(new Paragraph("1")));
                table.addCell(new Cell().add(new Paragraph("Alice")));
                table.addCell(new Cell()
                        .setTextAlignment(TextAlignment.CENTER)
                        .add(new Paragraph("10:00")));
                table.addCell(new Cell()
                        .setTextAlignment(TextAlignment.CENTER)
                        .add(new Paragraph("11:00")));
                table.addCell(new Cell().add(new Paragraph("Learn ukulele basic")));

                table.addCell(new Cell()
                        .setTextAlignment(TextAlignment.RIGHT)
                        .add(new Paragraph("2")));
                table.addCell(new Cell().add(new Paragraph("Bob")));
                table.addCell(new Cell()
                        .setTextAlignment(TextAlignment.CENTER)
                        .add(new Paragraph("09:00")));
                table.addCell(new Cell()
                        .setTextAlignment(TextAlignment.CENTER)
                        .add(new Paragraph("11:00")));
                table.addCell(new Cell()
                        .add(new Paragraph("Learn piano basic")));

                document.add(table);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}

Running the code will give you the result shown in the image below:

Maven Dependencies

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itext-core</artifactId>
    <version>8.0.3</version>
    <type>pom</type>
</dependency>

How do I add Image to a Table in iText 8?

By Wayan in iText PDF Last modified: March 11, 2024 0 Comment

In this example you’ll see how to add Image to a Table when creating a PDF document using iText 8. We start by finding the image resource using getResource() method and pass the absolute path to the resource name. The getResource() method return a java.net.URL object.

With this URL object in hand we then create the ImageData object using the ImageDataFactory.create() method. To the create() factory method we pass the URL object as a parameter. Finally, we create the Image object by calling the constructor of this class and passes the ImageData object as a parameter.

Here is the complete code snippet. Below we create a Premier League Ladder table showing club current position from position 1 to 10.

package org.kodejava.itext;

import com.itextpdf.io.image.ImageData;
import com.itextpdf.io.image.ImageDataFactory;
import com.itextpdf.kernel.colors.DeviceGray;
import com.itextpdf.kernel.pdf.PdfDocument;
import com.itextpdf.kernel.pdf.PdfWriter;
import com.itextpdf.layout.Document;
import com.itextpdf.layout.borders.Border;
import com.itextpdf.layout.element.Cell;
import com.itextpdf.layout.element.Image;
import com.itextpdf.layout.element.Paragraph;
import com.itextpdf.layout.element.Table;
import com.itextpdf.layout.properties.TextAlignment;
import com.itextpdf.layout.properties.UnitValue;
import com.itextpdf.layout.properties.VerticalAlignment;

import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

import static com.itextpdf.kernel.colors.DeviceGray.makeLighter;

public class TableExample {
    public static void main(String[] args) throws Exception {
        TableExample demo = new TableExample();
        demo.createTable();
    }

    private void createTable() throws Exception {
        String destination = "premier-league-ladder.pdf";
        PdfWriter writer = new PdfWriter(destination);
        PdfDocument pdf = new PdfDocument(writer);

        String[] headers = {"Position", "Club", "Played", "Won", "Drown", "Lost", "GF", "GA", "GD", "Points"};

        try (Document document = new Document(pdf)) {
            Table table = new Table(headers.length + 1);
            // Set table width to span the entire page
            table.setWidth(UnitValue.createPercentValue(100));

            URL plLogoFile = TableExample.class.getResource("/epl/pl-main-logo.png");
            ImageData plImageData = ImageDataFactory.create(Objects.requireNonNull(plLogoFile));

            table.addHeaderCell(new Cell().setBorder(Border.NO_BORDER)
                    .add(new Image(plImageData).scaleToFit(50, 50)));
            table.addHeaderCell(new Cell(1, 11).setBorder(Border.NO_BORDER)
                    .setVerticalAlignment(VerticalAlignment.MIDDLE)
                    .add(new Paragraph("Premier League Ladder").setFontSize(16).setBold()));

            for (String header : headers) {
                if (header.equals("Club")) {
                    table.addHeaderCell(new Cell(1, 2)
                            .setBackgroundColor(makeLighter(DeviceGray.GRAY))
                            .setBorderLeft(Border.NO_BORDER).setBorderRight(Border.NO_BORDER)
                            .setWidth(UnitValue.createPercentValue(28))
                            .add(new Paragraph(header)));
                } else {
                    table.addHeaderCell(newCell()
                            .setBackgroundColor(makeLighter(DeviceGray.GRAY))
                            .setWidth(UnitValue.createPercentValue(8))
                            .add(new Paragraph(header).setTextAlignment(TextAlignment.CENTER)));
                }
            }

            int position = 1;
            for (Club club : getTableData()) {
                String fileName = club.name().replace(' ', '_').toLowerCase() + ".png";
                URL logoFile = TableExample.class.getResource("/epl/logo/" + fileName);
                ImageData imageData = ImageDataFactory.create(Objects.requireNonNull(logoFile));

                table.addCell(newCell().add(newCenteredParagraph(String.valueOf(position++))));
                table.addCell(newCell().setWidth(UnitValue.createPercentValue(1))
                        .setVerticalAlignment(VerticalAlignment.MIDDLE)
                        .add(new Image(imageData).scaleAbsolute(16, 16)));
                table.addCell(newCell().setWidth(UnitValue.createPercentValue(27))
                        .add(new Paragraph(club.name())));
                table.addCell(newCell().add(newCenteredParagraph(String.valueOf(club.played()))));
                table.addCell(newCell().add(newCenteredParagraph(String.valueOf(club.won()))));
                table.addCell(newCell().add(newCenteredParagraph(String.valueOf(club.drawn()))));
                table.addCell(newCell().add(newCenteredParagraph(String.valueOf(club.lost()))));
                table.addCell(newCell().add(newCenteredParagraph(String.valueOf(club.goalsFor()))));
                table.addCell(newCell().add(newCenteredParagraph(String.valueOf(club.goalsAgainst()))));
                table.addCell(newCell().add(newCenteredParagraph(String.valueOf(club.goalDifference()))));
                table.addCell(newCell().add(newCenteredParagraph(String.valueOf(club.points()))));
            }

            document.add(table);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private Cell newCell() {
        return new Cell().setBorderLeft(Border.NO_BORDER).setBorderRight(Border.NO_BORDER);
    }

    private Paragraph newCenteredParagraph(String text) {
        return new Paragraph(text).setTextAlignment(TextAlignment.CENTER);
    }

    private List<Club> getTableData() {
        List<Club> clubs = new ArrayList<>();
        clubs.add(new Club("Arsenal", 20, 4, 4, 70, 24));
        clubs.add(new Club("Liverpool", 19, 6, 2, 64, 25));
        clubs.add(new Club("Man City", 19, 5, 3, 62, 27));
        clubs.add(new Club("Aston Villa", 17, 4, 6, 59, 37));
        clubs.add(new Club("Tottenham", 15, 5, 6, 55, 39));
        clubs.add(new Club("Man United", 15, 2, 11, 39, 39));
        clubs.add(new Club("West Ham", 12, 6, 9, 43, 47));
        clubs.add(new Club("Wolves", 12, 5, 11, 42, 44));
        clubs.add(new Club("Newcastle", 12, 4, 11, 57, 45));
        clubs.add(new Club("Brighton", 10, 9, 8, 49, 44));
        return clubs;
    }

    record Club(String name, int won, int drawn, int lost, int goalsFor, int goalsAgainst) {
        public int played() {
            return won + drawn + lost;
        }

        public int goalDifference() {
            return goalsFor - goalsAgainst;
        }

        public int points() {
            return (won * 3) + drawn;
        }
    }
}

And here is the output of the generated PDF table:

In the example above you can also see how to expand the width of the table to take the full width of the page.

table.setWidth(UnitValue.createPercentValue(100));

To span a table Cell to take multiple columns you can create a Cell object and specify the rowspan and colspan parameter.

table.addHeaderCell(new Cell(1, 2));

To remove the vertical border of the Cell you can set the left and right border by calling the setBorderLeft() and setBorderRight() method and passes Border.NO_BORDER as parameter.

new Cell().setBorderLeft(Border.NO_BORDER).setBorderRight(Border.NO_BORDER);

The data of the table is encapsulated using a record, this feature is introduced in Java 14, prior to this version you will create a simple POJO, which is a Java object with properties and related getters and setters method.

public record Club(String name, int won, int drawn, int lost, int goalsFor, int goalsAgainst) {}

Maven Dependencies

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itext-core</artifactId>
    <version>8.0.3</version>
    <type>pom</type>
</dependency>

How do I downgrade Android SDK emulator version?

By Wayan in Android Misc Last modified: February 12, 2024 0 Comment

I was trying to run Android Studio Emulator on my old 13-inch Mid 2012 MacBook Pro (Mac OS X Catalina, version 10.15.7). Every time I tried to start a Virtual Device it failed to start, it crashed all the time. Checking the idea.log, which located at $HOME/Library/Logs/Google/AndroidStudio2023.1/, give me some hints.

The log tells me that the current installed emulator was build for the newer version of MacBook Pro and newer Mac OS, in this case the Mac OS X 11.1. So to make the Android SDK Emulator run again on my MacBook Pro, I need to downgrade my Android emulator version.

Here are the clues from the log file:

2024-02-11 07:30:14,110 [7595298]   INFO - Emulator: Medium Phone API 27 - /Users/wayan/Library/Android/sdk/emulator/emulator -netdelay none -netspeed full -avd Medium_Phone_API_27 -qt-hide-window -grpc-use-token -idle-grpc-timeout 300
2024-02-11 07:30:14,200 [7595388]   INFO - Emulator: Medium Phone API 27 - Android emulator version 33.1.24.0 (build_id 11237101) (CL:N/A)
2024-02-11 07:30:14,200 [7595388]   INFO - Emulator: Medium Phone API 27 - Found systemPath /Users/wayan/Library/Android/sdk/system-images/android-27/google_apis_playstore/x86/
2024-02-11 07:30:15,424 [7596612]   INFO - Emulator: Medium Phone API 27 - dyld: Symbol not found: _vmnet_e
2024-02-11 07:30:15,428 [7596616]   INFO - Emulator: Medium Phone API 27 - nable_isolation_key
2024-02-11 07:30:15,429 [7596617]   INFO - Emulator: Medium Phone API 27 - Referenced
2024-02-11 07:30:15,429 [7596617]   INFO - Emulator: Medium Phone API 27 - from: /Users/wayan/Library/Android/sdk/emulator/qemu/darwin-x86_64/qemu-system-i386 (which was built for Mac OS X 11.1)
2024-02-11 07:30:15,429 [7596617]   INFO - Emulator: Medium Phone API 27 - Expected in: /System/Library/Frameworks/vmnet.framework/Versions/A/vmnet
2024-02-11 07:30:15,429 [7596617]   INFO - Emulator: Medium Phone API 27 - in /Users/wayan/Library/Android/sdk/emulator/qemu/darwin-x86_64/qemu-system-i386
2024-02-11 07:30:15,430 [7596618]   INFO - Emulator: Medium Phone API 27 - Process finished with exit code 134 (interrupted by signal 6: SIGABRT)
2024-02-11 07:30:15,431 [7596619] SEVERE - Emulator: Medium Phone API 27 - Emulator terminated with exit code 134
java.lang.Throwable: Emulator terminated with exit code 134
    at com.intellij.openapi.diagnostic.Logger.error(Logger.java:202)
    at com.android.tools.idea.avdmanager.EmulatorProcessHandler$ConsoleListener.onTextAvailable(EmulatorProcessHandler.kt:89)
    at jdk.internal.reflect.GeneratedMethodAccessor40.invoke(Unknown Source)

So these are the steps that I need to do to downgrade it:

Download an older version of Android Emulator, here is the link to Android Emulator archive: https://developer.android.com/studio/emulator_archive.
I download version 30.7.4.
Locate the current emulator directory, which is under my Android SDK installation directory at $HOME/Library/Android/sdk.
Rename the existing emulator directory from emulator to emulator_original.
Next, I unzip the downloaded emulator, emulator-darwin_x64-7324830.zip, and copy it to the same location where the original emulator was located.
In the SDK installation directory, run the following command xattr -dr com.apple.quarantine emulator/ from the terminal app to clear the quarantine attribute on the emulator package.
Copy the package.xml file from the emulator_original directory to the emulator directory.
Change the emulator version in the package.xml file, it located at the end of the file. It should look something like:

<revision><major>30</major><minor>7</minor><micro>4</micro></revision>

After downgrading the emulator, I restarted the Android Studio, and I can now start the emulator successfully and able to run and test my application in the old MacBook Pro again.