How do I find the difference between two times?

The following code snippet show you how to find the difference between two time objects represented by LocalTime class. To get the difference between two LocalTime objects we can use the Duration.between() method. This method returns a Duration object, to get the difference in seconds we call the getSeconds() method.

Here a code snippet to demonstrate it.

package org.kodejava.datetime;

import java.time.*;

public class TimeDifference {
    public static void main(String[] args) {
        LocalTime start = LocalTime.now();
        LocalTime end = LocalTime.of(16, 59, 55);
        Duration duration = Duration.between(start, end);

        System.out.printf("Seconds between %s and %s is: %s seconds.%n",
                start, end, duration.getSeconds());

        diffLocalDateTime();
        diffInstant();
    }

    /**
     * Difference between two LocalDateTime objects.
     */
    public static void diffLocalDateTime() {
        LocalDateTime dt1 = LocalDateTime.now();
        LocalDateTime dt2 = LocalDateTime.now(ZoneId.of("GMT+0"));
        Duration duration = Duration.between(dt1, dt2);
        System.out.printf("Duration = %s seconds.%n", duration.getSeconds());
    }

    /**
     * Difference between two Instant objects.
     */
    public static void diffInstant() {
        Instant instant1 = Instant.now();
        Instant instant2 = Instant.EPOCH;
        Duration duration = Duration.between(instant1, instant2);
        System.out.printf("Duration = %s seconds.%n", duration.getSeconds());
    }
}

Using the Duration.between() we can also get the difference between two LocalDateTime objects and two Instant object as seen in the diffLocalDateTime() method and diffInstant method in the code snippet above.

The result of the code snippet:

Seconds between 15:05:35.401317900 and 16:59:55 is: 6859 seconds.
Duration = -28800 seconds.
Duration = -1637132736 seconds.

How do I specify the Java compiler version in a pom.xml file?

When you need to compile a project for a specific Java version you can configure maven compiler plugin to set the source and the target version. The following pom.xml file configuration show you how to do it.

<project>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.2</version>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>    

Invalid value for the source and the target version in our project will make our project compilation process failed. For example when we try to use the diamond operator (<>) which available in Java 7, while the maven compiler plugin is set to version 1.5, can produce compiler error like this:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project servlet-example: Compilation failure
[ERROR] /Users/wsaryada/Studio/kodejava.org/webapp-example/servlet-example/src/main/java/org/kodejava/example/servlet/SessionCounter.java:[10,51] diamond operator is not supported in -source 1.5
[ERROR] (use -source 7 or higher to enable diamond operator)

How do I parse negative number in parentheses?

In financial application negative numbers are often represented in parentheses. In this post we will learn how we can parse or convert the negative number in parentheses to produce the represented number value. To parse text / string to a number we can use the java.text.DecimalFormat class.

Beside number in parentheses, in this example we also parse negative number that use the minus sign with the currency symbol like $. Let’s jump to the code snippet below:

package org.kodejava.text;

import java.text.DecimalFormat;

public class NegativeNumberParse {
    // Pattern for parsing negative number.
    public static final String PATTERN1 = "#,##0.00;(#,##0.00)";
    public static final String PATTERN2 = "$#,##0.00;-$#,##0.00";

    public static void main(String[] args) throws Exception {
        DecimalFormat df = new DecimalFormat(PATTERN1);

        String number1 = "(1000)";
        String number2 = "(1,500.99)";

        System.out.println("number1 = " + df.parse(number1));
        System.out.println("number2 = " + df.parse(number2));

        df = (DecimalFormat) DecimalFormat.getInstance();
        df.applyPattern(PATTERN2);

        String number3 = "-$1000";
        String number4 = "-$1,500.99";

        System.out.println("number3 = " + df.parse(number3));
        System.out.println("number4 = " + df.parse(number4));
    }
}

And here are the results of our code snippet above:

number1 = -1000
number2 = -1500.99
number3 = -1000
number4 = -1500.99

If you need to display or format negative numbers in parentheses you can take a look at the following example How do I display negative number in parentheses?.

Why do I get NotOLE2FileException: Invalid header signature error?

When I was creating the code snippet for the How do I replace text in Microsoft Word document using Apache POI? I got the following error when running the snippet . As additional information, the code snippet for the Kodejava website is written as a Maven project.

org.apache.poi.poifs.filesystem.NotOLE2FileException: Invalid header signature; read 0xE011BDBFEFBDBFEF, expected 0xE11AB1A1E011CFD0 – Your file appears not to be a valid OLE2 document

This error message was produce when the code trying to open a Word document. The Apache POI reports that the Word document has an invalid header signature, not a valid OLE2 document. Comparing the original document with the document under maven’s target directory I found out that the file size was different. This could mean that something alter the document and corrupt the header.

After doing some googling, I found out that this error is due to maven resource filtering. The maven resource filtering process cause the Word document header corrupt during the copy phase. The solution to this problem is to make sure that the filtering process is set to false. The pom.xml of the maven project should be altered to have the following configuration.

<build>
    <resources>
        <resource>
            <directory>src/main/resources</directory>
            <filtering>false</filtering>
        </resource>
    </resources>
</build>

How do I replace text in Microsoft Word document using Apache POI?

The code snippet below show you how you can replace string in Microsoft Word document using the Apache POI library. The class below have three method, the openDocument(), saveDocument() and replaceText().

The routine for replacing text is implemented in the replaceText() method. This method take the HWPFDocument, the String to find and the String to replace it as parameters. The openDocument() opens the Word document. When the text replacement is done the Word document will be saved by the saveDocument() method.

And here is the complete code snippet. It will replace every dolor texts into d0l0r texts in the source document, the lipsum.doc, and save the result in a new document called new-lipsum.doc.

package org.kodejava.poi;

import org.apache.poi.hwpf.HWPFDocument;
import org.apache.poi.hwpf.usermodel.CharacterRun;
import org.apache.poi.hwpf.usermodel.Paragraph;
import org.apache.poi.hwpf.usermodel.Range;
import org.apache.poi.hwpf.usermodel.Section;
import org.apache.poi.poifs.filesystem.POIFSFileSystem;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.URL;

public class WordReplaceText {
    private static final String SOURCE_FILE = "lipsum.doc";
    private static final String OUTPUT_FILE = "new-lipsum.doc";

    public static void main(String[] args) throws Exception {
        WordReplaceText instance = new WordReplaceText();
        try (HWPFDocument doc = instance.openDocument(SOURCE_FILE)) {
            if (doc != null) {
                HWPFDocument newDoc = instance.replaceText(doc, "dolor", "d0l0r");
                instance.saveDocument(newDoc, OUTPUT_FILE);
            }
        }
    }

    private HWPFDocument replaceText(HWPFDocument doc, String findText, String replaceText) {
        Range range = doc.getRange();
        for (int numSec = 0; numSec < range.numSections(); ++numSec) {
            Section sec = range.getSection(numSec);
            for (int numPara = 0; numPara < sec.numParagraphs(); numPara++) {
                Paragraph para = sec.getParagraph(numPara);
                for (int numCharRun = 0; numCharRun < para.numCharacterRuns(); numCharRun++) {
                    CharacterRun charRun = para.getCharacterRun(numCharRun);
                    String text = charRun.text();
                    if (text.contains(findText)) {
                        charRun.replaceText(findText, replaceText);
                    }
                }
            }
        }
        return doc;
    }

    private HWPFDocument openDocument(String file) throws Exception {
        URL res = getClass().getClassLoader().getResource(file);
        HWPFDocument document = null;
        if (res != null) {
            document = new HWPFDocument(new POIFSFileSystem(
                    new File(res.getPath())));
        }
        return document;
    }

    private void saveDocument(HWPFDocument doc, String file) {
        try (FileOutputStream out = new FileOutputStream(file)) {
            doc.write(out);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.apache.poi</groupId>
        <artifactId>poi</artifactId>
        <version>5.2.5</version>
    </dependency>
    <dependency>
        <groupId>org.apache.poi</groupId>
        <artifactId>poi-scratchpad</artifactId>
        <version>5.2.5</version>
    </dependency>
</dependencies>

Maven Central Maven Central