I added a method to convert an excel file to CSV. I added a method to check if there are any sheets based on their position or name. Other methods for closing a workbook and the various classes of streams.

Author: MBenincasa

pom.xml

@@ -9,7 +9,7 @@
     <version>1.0-SNAPSHOT</version>
     <packaging>jar</packaging>
     <name>java-excel-tools</name>
-    <description>Library with tools to work with excel files</description>
+    <description>Library with tools to work with Excel files</description>
 
     <properties>
         <maven.compiler.source>17</maven.compiler.source>
@@ -39,5 +39,10 @@
             <artifactId>commons-beanutils</artifactId>
             <version>1.9.4</version>
         </dependency>
+        <dependency>
+            <groupId>com.opencsv</groupId>
+            <artifactId>opencsv</artifactId>
+            <version>5.7.1</version>
+        </dependency>
     </dependencies>
 </project>

src/main/java/samples/convertExcelFileToCsvFile/Main.java

@@ -0,0 +1,24 @@
+package samples.convertExcelFileToCsvFile;
+
+import tools.implementations.ExcelConverterImpl;
+import tools.interfaces.ExcelConverter;
+
+import java.io.File;
+
+public class Main {
+
+    public static void main(String[] args) {
+
+        ExcelConverter excelConverter = new ExcelConverterImpl();
+        File excelFile = new File("./src/main/resources/employee.xlsx");
+
+        try {
+            System.out.println("Start the conversion...");
+            File csvFile = excelConverter.excelToCsv(excelFile, "./src/main/resources/", "employee", "Employee");
+            System.out.println("The file is ready. Path: " + csvFile.getAbsolutePath());
+        } catch (Exception e) {
+            System.err.println("There was an error. Check the console");
+            throw new RuntimeException(e);
+        }
+    }
+}

src/main/java/samples/sheetSample/Main.java

@@ -1,7 +1,10 @@
 package samples.sheetSample;
 
+import org.apache.poi.ss.usermodel.Workbook;
+import tools.implementations.ExcelWorkbookUtilsImpl;
 import tools.interfaces.ExcelSheetUtils;
 import tools.implementations.ExcelSheetUtilsImpl;
+import tools.interfaces.ExcelWorkbookUtils;
 
 import java.io.File;
 import java.util.List;
@@ -10,6 +13,7 @@ public class Main {
 
     public static void main(String[] args) {
 
+        ExcelWorkbookUtils excelWorkbookUtils = new ExcelWorkbookUtilsImpl();
         ExcelSheetUtils excelSheetUtils = new ExcelSheetUtilsImpl();
         File file = new File("./src/main/resources/employee.xlsx");
 
@@ -22,6 +26,14 @@ public static void main(String[] args) {
             System.out.println("Sheet index: " + sheetIndex);
             String sheetName = excelSheetUtils.getNameByIndex(file, 0);
             System.out.println("Sheet name: " + sheetName);
+
+            Workbook workbook = excelWorkbookUtils.open(file);
+            String sheetNameTest = "test";
+            int sheetIndexTest = 0;
+            Boolean isPresentByName = excelSheetUtils.isPresent(workbook, sheetNameTest);
+            System.out.println("Sheet is: " + sheetNameTest + " is present: " + isPresentByName);
+            Boolean isPresentByPosition = excelSheetUtils.isPresent(workbook, 0);
+            System.out.println("Sheet index: " + sheetIndexTest + " is present: " + isPresentByPosition);
         } catch (Exception e) {
             System.err.println("There was an error. Check the console");
             throw new RuntimeException(e);

src/main/java/tools/implementations/ExcelConverterImpl.java

@@ -3,6 +3,7 @@
 import annotations.ExcelBodyStyle;
 import annotations.ExcelField;
 import annotations.ExcelHeaderStyle;
+import com.opencsv.CSVWriter;
 import enums.ExcelExtension;
 import exceptions.*;
 import org.apache.commons.beanutils.PropertyUtils;
@@ -160,6 +161,63 @@ public List<?> excelToObjects(File file, Class<?> clazz, String sheetName) throw
         return resultList;
     }
 
+    @Override
+    public File excelToCsv(File fileInput) throws FileAlreadyExistsException, OpenWorkbookException, SheetNotFoundException, ExtensionNotValidException, IOException {
+        return excelToCsv(fileInput, System.getProperty("java.io.tmpdir"), fileInput.getName().split("\\.")[0].trim(), null);
+    }
+
+    @Override
+    public File excelToCsv(File fileInput, String sheetName) throws FileAlreadyExistsException, OpenWorkbookException, SheetNotFoundException, ExtensionNotValidException, IOException {
+        return excelToCsv(fileInput, System.getProperty("java.io.tmpdir"), fileInput.getName().split("\\.")[0].trim(), sheetName);
+    }
+
+    @Override
+    public File excelToCsv(File fileInput, String path, String filename) throws FileAlreadyExistsException, OpenWorkbookException, SheetNotFoundException, ExtensionNotValidException, IOException {
+        return excelToCsv(fileInput, path, filename, null);
+    }
+
+    @Override
+    public File excelToCsv(File fileInput, String path, String filename, String sheetName) throws ExtensionNotValidException, IOException, OpenWorkbookException, SheetNotFoundException, FileAlreadyExistsException {
+        /* Check extension */
+        ExcelUtils excelUtils = new ExcelUtilsImpl();
+        String extension = excelUtils.checkExtension(fileInput.getName());
+
+        /* Open file excel */
+        ExcelWorkbookUtils excelWorkbookUtils = new ExcelWorkbookUtilsImpl();
+        FileInputStream fileInputStream = new FileInputStream(fileInput);
+        Workbook workbook = excelWorkbookUtils.open(fileInputStream, extension);
+        ExcelSheetUtils excelSheetUtils = new ExcelSheetUtilsImpl();
+        Sheet sheet = (sheetName == null || sheetName.isEmpty())
+                ? excelSheetUtils.open(workbook)
+                : excelSheetUtils.open(workbook, sheetName);
+
+        /* Create output file */
+        String pathname = this.getPathname(path, filename, "csv");
+        File csvFile = new File(pathname);
+
+        if (csvFile.exists()) {
+            throw new FileAlreadyExistsException("There is already a file with this pathname: " + csvFile.getAbsolutePath());
+        }
+
+        /* Write output file */
+        FileWriter fileWriter = new FileWriter(csvFile);
+        CSVWriter csvWriter = new CSVWriter(fileWriter);
+
+        DataFormatter formatter = new DataFormatter(true);
+        for (Row row : sheet) {
+            List<String> data = new LinkedList<>();
+            for (int i = 0; i < row.getLastCellNum(); i++) {
+                data.add(formatter.formatCellValue(row.getCell(i)));
+            }
+            csvWriter.writeNext(data.toArray(data.toArray(new String[0])));
+        }
+
+        /* Close file */
+        excelWorkbookUtils.close(workbook, fileInputStream, csvWriter);
+
+        return csvFile;
+    }
+
     private Map<Integer, String> getHeaderNames(Sheet sheet, Field[] fields) throws HeaderNotPresentException {
         Map<String, String> fieldNames = new HashMap<>();
         for (Field field : fields) {
@@ -323,11 +381,15 @@ private void setAutoSizeColumn(Sheet sheet, Field[] fields, Class<?> clazz) {
     }
 
     private String getPathname(String path, String filename, ExcelExtension extension) {
+        return getPathname(path, filename, extension.getExt());
+    }
+
+    private String getPathname(String path, String filename, String extension) {
         path = path.replaceAll("\\\\", "/");
         if (path.charAt(path.length() - 1) != '/') {
             path += '/';
         }
 
-        return path + filename + '.' + extension.getExt();
+        return path + filename + '.' + extension;
     }
 }

src/main/java/tools/implementations/ExcelSheetUtilsImpl.java

@@ -208,4 +208,14 @@ public Sheet openOrCreate(Workbook workbook, String sheetName) {
         Sheet sheet = workbook.getSheet(sheetName);
         return sheet == null ? workbook.createSheet(sheetName) : sheet;
     }
+
+    @Override
+    public Boolean isPresent(Workbook workbook, String sheetName) {
+        return workbook.getSheet(sheetName) != null;
+    }
+
+    @Override
+    public Boolean isPresent(Workbook workbook, Integer position) {
+        return workbook.getSheetAt(position) != null;
+    }
 }

src/main/java/tools/implementations/ExcelWorkbookUtilsImpl.java

@@ -1,5 +1,6 @@
 package tools.implementations;
 
+import com.opencsv.CSVWriter;
 import enums.ExcelExtension;
 import exceptions.ExtensionNotValidException;
 import exceptions.OpenWorkbookException;
@@ -87,4 +88,18 @@ public void close(Workbook workbook, FileOutputStream fileOutputStream) throws I
         workbook.close();
         fileOutputStream.close();
     }
+
+    @Override
+    public void close(Workbook workbook, FileOutputStream fileOutputStream, FileInputStream fileInputStream) throws IOException {
+        workbook.close();
+        fileInputStream.close();
+        fileOutputStream.close();
+    }
+
+    @Override
+    public void close(Workbook workbook, FileInputStream fileInputStream, CSVWriter writer) throws IOException {
+        workbook.close();
+        fileInputStream.close();
+        writer.close();
+    }
 }

src/main/java/tools/interfaces/ExcelConverter.java

@@ -37,4 +37,12 @@ public interface ExcelConverter {
     List<?> excelToObjects(File file, Class<?> clazz) throws ExtensionNotValidException, IOException, OpenWorkbookException, InstantiationException, IllegalAccessException, InvocationTargetException, NoSuchMethodException, SheetNotFoundException, HeaderNotPresentException;
 
     List<?> excelToObjects(File file, Class<?> clazz, String sheetName) throws ExtensionNotValidException, IOException, OpenWorkbookException, InvocationTargetException, IllegalAccessException, NoSuchMethodException, InstantiationException, SheetNotFoundException, HeaderNotPresentException;
+
+    File excelToCsv(File fileInput) throws FileAlreadyExistsException, OpenWorkbookException, SheetNotFoundException, ExtensionNotValidException, IOException;
+
+    File excelToCsv(File fileInput, String sheetName) throws FileAlreadyExistsException, OpenWorkbookException, SheetNotFoundException, ExtensionNotValidException, IOException;
+
+    File excelToCsv(File fileInput, String path, String filename) throws FileAlreadyExistsException, OpenWorkbookException, SheetNotFoundException, ExtensionNotValidException, IOException;
+
+    File excelToCsv(File fileInput, String path, String filename, String sheetName) throws ExtensionNotValidException, IOException, OpenWorkbookException, SheetNotFoundException, FileAlreadyExistsException;
 }

src/main/java/tools/interfaces/ExcelSheetUtils.java

@@ -41,4 +41,8 @@ public interface ExcelSheetUtils {
     Sheet open(Workbook workbook, Integer position) throws SheetNotFoundException;
 
     Sheet openOrCreate(Workbook workbook, String sheetName);
+
+    Boolean isPresent(Workbook workbook, String sheetName);
+
+    Boolean isPresent(Workbook workbook, Integer position);
 }

src/main/java/tools/interfaces/ExcelWorkbookUtils.java

@@ -1,5 +1,6 @@
 package tools.interfaces;
 
+import com.opencsv.CSVWriter;
 import enums.ExcelExtension;
 import exceptions.ExtensionNotValidException;
 import exceptions.OpenWorkbookException;
@@ -24,4 +25,8 @@ public interface ExcelWorkbookUtils {
     void close(Workbook workbook, FileInputStream fileInputStream) throws IOException;
 
     void close(Workbook workbook, FileOutputStream fileOutputStream) throws IOException;
+
+    void close(Workbook workbook, FileOutputStream fileOutputStream, FileInputStream fileInputStream) throws IOException;
+
+    void close(Workbook workbook, FileInputStream fileInputStream, CSVWriter writer) throws IOException;
 }