文件處理是任何程式語言的重要組成部分。在 Java 中,java.io 和 java.nio 套件提供了用於讀取和寫入檔案(文字和二進位)的強大類別。本指南涵蓋了 Java 檔案處理的基礎知識,包括範例、挑戰和技巧,可協助您掌握主題。
Java提供了多種讀取文字檔案的方法,但最常見、最簡單的方法是使用BufferedReader和FileReader。
範例:
import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; public class TextFileReader { public static void main(String[] args) { try (BufferedReader reader = new BufferedReader(new FileReader("example.txt"))) { String line; while ((line = reader.readLine()) != null) { System.out.println(line); } } catch (IOException e) { e.printStackTrace(); } } }
重點:
使用 BufferedWriter 和 FileWriter 寫入文字檔案同樣簡單。
範例:
import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; public class TextFileWriter { public static void main(String[] args) { try (BufferedWriter writer = new BufferedWriter(new FileWriter("example.txt"))) { writer.write("Hello, World!"); writer.newLine(); writer.write("This is a text file."); } catch (IOException e) { e.printStackTrace(); } } }
挑戰:寫一個 Java 程序,逐行讀取文字檔案並計算檔案中的單字數。
二進位檔案需要不同的方法,因為它們不是人類可讀的。 Java 的 FileInputStream 和 FileOutputStream 類別非常適合讀取和寫入二進位資料。
範例:
import java.io.FileInputStream; import java.io.IOException; public class BinaryFileReader { public static void main(String[] args) { try (FileInputStream inputStream = new FileInputStream("example.dat")) { int byteData; while ((byteData = inputStream.read()) != -1) { System.out.print(byteData + " "); } } catch (IOException e) { e.printStackTrace(); } } }
重點:
範例:
import java.io.FileOutputStream; import java.io.IOException; public class BinaryFileWriter { public static void main(String[] args) { try (FileOutputStream outputStream = new FileOutputStream("example.dat")) { outputStream.write(65); // Writes a single byte to the file outputStream.write(new byte[]{66, 67, 68}); // Writes multiple bytes to the file } catch (IOException e) { e.printStackTrace(); } } }
挑戰:編寫一個程序,將二進位(如圖像)從一個位置複製到另一個位置。
Java 的 java.util.zip 套件可讓您使用 ZIP 檔案。您可以使用 ZipInputStream 從 ZIP 檔案中提取檔案。
import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.util.zip.ZipEntry; import java.util.zip.ZipInputStream; public class ZipFileReader { public static void main(String[] args) { try (ZipInputStream zipStream = new ZipInputStream(new FileInputStream("example.zip"))) { ZipEntry entry; while ((entry = zipStream.getNextEntry()) != null) { System.out.println("Extracting: " + entry.getName()); FileOutputStream outputStream = new FileOutputStream(entry.getName()); byte[] buffer = new byte[1024]; int len; while ((len = zipStream.read(buffer)) > 0) { outputStream.write(buffer, 0, len); } outputStream.close(); zipStream.closeEntry(); } } catch (IOException e) { e.printStackTrace(); } } }
重點:
挑戰:編寫一個 Java 程序,從 ZIP 檔案中讀取所有 .txt 檔案並將其內容列印到控制台。
Java 本身不支援寫入 Microsoft Office 檔案(例如 .docx 或 .xlsx),但可以使用 Apache POI 等程式庫來實現此目的。
範例:
import org.apache.poi.ss.usermodel.*; import org.apache.poi.xssf.usermodel.XSSFWorkbook; import java.io.FileOutputStream; import java.io.IOException; public class ExcelFileWriter { public static void main(String[] args) { Workbook workbook = new XSSFWorkbook(); Sheet sheet = workbook.createSheet("Sheet1"); Row row = sheet.createRow(0); Cell cell = row.createCell(0); cell.setCellValue("Hello, Excel!"); try (FileOutputStream outputStream = new FileOutputStream("example.xlsx")) { workbook.write(outputStream); } catch (IOException e) { e.printStackTrace(); } } }
挑戰:寫一個 Java 程序,建立一個包含多個工作表的 Excel 文件,每個工作表包含一個資料表。
Java 提供了多種處理 XML 檔案的方法。 javax.xml.parsers 套件通常用於此目的。
範例:
import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import org.w3c.dom.Document; import org.w3c.dom.NodeList; import java.io.File; public class XMLFileReader { public static void main(String[] args) { try { File file = new File("example.xml"); DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder(); Document doc = builder.parse(file); NodeList nodeList = doc.getElementsByTagName("tagname"); for (int i = 0; i < nodeList.getLength(); i++) { System.out.println(nodeList.item(i).getTextContent()); } } catch (Exception e) { e.printStackTrace(); } } }
範例:
import javax.xml.parsers.DocumentBuilderFactory; import javax.xml.parsers.ParserConfigurationException; import javax.xml.transform.*; import javax.xml.transform.dom.DOMSource; import javax.xml.transform.stream.StreamResult; import org.w3c.dom.Document; import org.w3c.dom.Element; import java.io.File; public class XMLFileWriter { public static void main(String[] args) { try { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder(); Document doc = builder.newDocument(); Element root = doc.createElement("root"); doc.appendChild(root); Element child = doc.createElement("child"); child.appendChild(doc.createTextNode("Hello, XML!")); root.appendChild(child); TransformerFactory transformerFactory = TransformerFactory.newInstance(); Transformer transformer = transformerFactory.newTransformer(); transformer.setOutputProperty(OutputKeys.INDENT, "yes"); DOMSource source = new DOMSource(doc); StreamResult result = new StreamResult(new File("example.xml")); transformer.transform(source, result); } catch (ParserConfigurationException | TransformerException e) { e.printStackTrace(); } } }
挑戰:建立一個 Java 程序,讀取 XML 設定檔並以人類可讀的格式輸出設定。
處理檔案時,由於檔案遺失、權限錯誤或意外的資料格式等問題,異常很常見。正確的異常處理對於健壯的程序至關重要。
最佳實務:
範例:
import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; public class FileExceptionHandling { public static void main(String[] args) { try (BufferedReader reader = new BufferedReader(new FileReader("example.txt"))) { String line; while ((line = reader.readLine()) != null) { System.out.println(line); } } catch (IOException e) { System.err.println("An I/O error occurred: " + e.getMessage()); } } }
File handling in Java is a powerful feature, enabling you to work with various file types, from simple text files to complex XML and binary files. By mastering these techniques, you'll be well-equipped to handle any file-based tasks in your Java applications.
Final Challenge: Combine reading and writing techniques to create a program that reads data from an Excel file, processes it, and then writes the results to a new XML file.
Tips & Tricks:
Happy coding!
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