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Excel files operations using Apache POI

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Yash edited this page Jul 31, 2018 · 1 revision

Excel files (spreadsheets) are widely used by people all over the world for various tasks related to organization, analysis, and storage of tabular data. Since excel files are so common, we developers often encounter use-cases when we need to read data from an excel file or generate a report in excel format.

In this article, I’ll show you how to read excel files in Java using a very simple yet powerful open source library called Apache POI.

Apache POI excel library revolves around following four key interfaces -

  • Workbook: A workbook is the high-level representation of a Spreadsheet.
  • Sheet: A workbook may contain many sheets. The sample excel file that we looked at in the previous section has two sheets - Employee and Department
  • Row: As the name suggests, It represents a row in the spreadsheet.
  • Cell: A cell represents a column in the spreadsheet.

Apache POI library consists of two different implementations for all the above interfaces.

  • XSSFWorkbook and HSSFWorkbook are classes which act as an Excel Workbook
  • HSSFSheet and XSSFSheet are classes which act as an Excel Worksheet
  • HSSF (Horrible SpreadSheet Format): HSSF implementations of POI’s high-level interfaces like HSSFWorkbook, HSSFSheet, HSSFRow and HSSFCell are used to work with excel files of the older binary file format - .xls (Microsoft Excel 2003 file)
  • XSSF (XML SpreadSheet Format): XSSF implementations are used to work with the newer XML based file format - .xlsx. (Microsoft Excel 2007 file or later)

Image Reference

Maven dependencies to your pom.xml file

<!-- https://mvnrepository.com/artifact/org.apache.poi/poi -->
<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi</artifactId>
    <version>3.17</version>
</dependency>

<!-- https://mvnrepository.com/artifact/org.apache.poi/poi-ooxml -->
<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi-ooxml</artifactId>
    <version>3.17</version>
</dependency>

Example to read an Excel file

public class ApachePOIExcelRead {
    private static final String FILE_NAME = "/tmp/MyFirstExcel.xlsx";
    public static void main(String[] args) {
        try {
            FileInputStream excelFile = new FileInputStream(new File(FILE_NAME));
            Workbook workbook = new XSSFWorkbook(excelFile);
            Sheet datatypeSheet = workbook.getSheetAt(0);
            Iterator<Row> iterator = datatypeSheet.iterator();

            while (iterator.hasNext()) {
                Row currentRow = iterator.next();
                Iterator<Cell> cellIterator = currentRow.iterator();
                while (cellIterator.hasNext()) {
                    Cell currentCell = cellIterator.next();
                    //getCellTypeEnum shown as deprecated for version 3.15
                    //getCellTypeEnum ill be renamed to getCellType starting from version 4.0
                    if (currentCell.getCellTypeEnum() == CellType.STRING) {
                        System.out.print(currentCell.getStringCellValue() + "--");
                    } else if (currentCell.getCellTypeEnum() == CellType.NUMERIC) {
                        System.out.print(currentCell.getNumericCellValue() + "--");
                    }
                }
                System.out.println();
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

OpenJDK Downloads : In a class-based object-oriented language, in general, state is carried by instances, methods are carried by classes, and inheritance is only of structure and behavior. Basic, Refactoring Techniques

Method signature: It consists of method name and parameter list (number/type/order of the parameters). methodName(parametersList y). An instance method in a subclass with the same signature and return type as an instance method in the super-class overrides the super-class's method.

Java OOP concepts
Class  - Collection of a common features of a group of object [static/instance Fields, blocks and Methods]
Object - Instance of a class (instance fields)
Abstraction - Process of hiding complex info and providing required info like API, Marker Interfaces ...
Encapsulation(Security) - Class Binding up with data members(fields) and member functions.
Inheritance  (Reusability by placing common code in single class)
 1. Multilevel - {A -> B -> C} 2. Multiple - Diamond problem {A <- (B) -> C} [Java not supports] 3. Cyclic {A <-> B} [Java not supports]
 * Is-A   Relation - Class A extends B
 * Hash-A Relation - Class A { B obj = new B(); } - (Composition/Aggregation)
Polymorphism (Flexibility) 1. Compile-Time Overloading    2. Runtime Overriding  [Greek - "many forms"]


int[] arr = {1,2,3}; int arrLength = arr.length;   // Fixed length of sequential blocks to hold same data type
String str = "Yash"; int strLength = str.length(); // Immutable Object value can't be changed.

List<?> collections = new ArrayList<String>(); int collectionGroupSize = collections.size();
Map<?, ?> mapEntry = new HashMap<String, String>();
Set<?> keySet = mapEntry.keySet(); // Set of Key's
Set<?> entrySet = mapEntry.entrySet(); // Set of Entries [Key, Value]

// Immutable Objects once created they can't be modified. final class Integer/String/Employee
Integer val = Integer.valueOf("100"); String str2 = String.valueOf(100); // Immutable classes
final class Employee { // All Wrapper classes, java.util.UUID, java.io.File ...
    private final String empName; // Field as Final(values can be assigned only once) Only getter functions.
    public Employee(String name) { this.empName = name; }
}

Native Java Code for Hashtable.h, Hashtable.cpp SQL API.

You can check your current JDK and JRE versions on your command prompt respectively,

  • JDK javac -version [C:\Program Files\Java\jdk1.8.0_121\bin] o/p: javac 1.8.0_121
  • JRE java -version [C:\Program Files\Java\jdk1.8.0_121\bin] o/P: java version "1.8.0_102"

JAVA_HOME - Must be set to JDK otherwise maven projects leads to compilation error. [ERROR] No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK? C:\Softwares\OpenJDK\, 7-zip

Fatal error compiling: invalid target release: JRE and JDK must be of same version 1.8.0.XXX

Disable TLS 1.0 and 1.1security-libs/javax.net.ssl: TLS 1.0 and 1.1 are versions of the TLS protocol that are no longer considered secure and have been superseded by more secure and modern versions (TLS 1.2 and 1.3).

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