以前導出總是用POI導出為Excel文件，后來當我了解到CSV以后，我發現速度飛快。

如果導出的數據不要求格式、樣式、公式等等，建議最好導成CSV文件，因為真的很快。

雖然我們可以用Java再帶的文件相關的類去操作以生成一個CSV文件，但事實上有好多第三方類庫也提供了類似的功能。

這里我們使用apache提供的commons-csv組件

Commons CSV

文檔在這里

http://commons.apache.org/

http://commons.apache.org/proper/commons-csv/

http://commons.apache.org/proper/commons-csv/user-guide.html

先看一下具體用法

@Test public void testWrite() throws Exception { FileOutputStream fos = new FileOutputStream('E:/cjsworkspace/cjs-excel-demo/target/abc.csv'); OutputStreamWriter osw = new OutputStreamWriter(fos, 'GBK'); CSVFormat csvFormat = CSVFormat.DEFAULT.withHeader('姓名', '年齡', '家鄉'); CSVPrinter csvPrinter = new CSVPrinter(osw, csvFormat);// csvPrinter = CSVFormat.DEFAULT.withHeader('姓名', '年齡', '家鄉').print(osw); for (int i = 0; i < 10; i++) { csvPrinter.printRecord('張三', 20, '湖北'); } csvPrinter.flush(); csvPrinter.close(); } @Test public void testRead() throws IOException { InputStream is = new FileInputStream('E:/cjsworkspace/cjs-excel-demo/target/abc.csv'); InputStreamReader isr = new InputStreamReader(is, 'GBK'); Reader reader = new BufferedReader(isr); CSVParser parser = CSVFormat.EXCEL.withHeader('name', 'age', 'jia').parse(reader);// CSVParser csvParser = CSVParser.parse(reader, CSVFormat.DEFAULT.withHeader('name', 'age', 'jia')); List<CSVRecord> list = parser.getRecords(); for (CSVRecord record : list) { System.out.println(record.getRecordNumber() + ':' + record.get('name') + ':' + record.get('age') + ':' + record.get('jia')); } parser.close(); } /** * Parsing an Excel CSV File */ @Test public void testParse() throws Exception { Reader reader = new FileReader('C:/Users/Administrator/Desktop/abc.csv'); CSVParser parser = CSVFormat.EXCEL.parse(reader); for (CSVRecord record : parser.getRecords()) { System.out.println(record); } parser.close(); } /** * Defining a header manually */ @Test public void testParseWithHeader() throws Exception { Reader reader = new FileReader('C:/Users/Administrator/Desktop/abc.csv'); CSVParser parser = CSVFormat.EXCEL.withHeader('id', 'name', 'code').parse(reader); for (CSVRecord record : parser.getRecords()) { System.out.println(record.get('id') + ',' + record.get('name') + ',' + record.get('code')); } parser.close(); } /** * Using an enum to define a header */ enum MyHeaderEnum { ID, NAME, CODE; } @Test public void testParseWithEnum() throws Exception { Reader reader = new FileReader('C:/Users/Administrator/Desktop/abc.csv'); CSVParser parser = CSVFormat.EXCEL.withHeader(MyHeaderEnum.class).parse(reader); for (CSVRecord record : parser.getRecords()) { System.out.println(record.get(MyHeaderEnum.ID) + ',' + record.get(MyHeaderEnum.NAME) + ',' + record.get(MyHeaderEnum.CODE)); } parser.close(); } private List<Map<String, String>> recordList = new ArrayList<>(); @Before public void init() { for (int i = 0; i < 5; i++) { Map<String, String> map = new HashMap<>(); map.put('name', 'zhangsan'); map.put('code', '001'); recordList.add(map); } } @Test public void writeMuti() throws InterruptedException { ExecutorService executorService = Executors.newFixedThreadPool(3); CountDownLatch doneSignal = new CountDownLatch(2); executorService.submit(new exprotThread('E:/0.csv', recordList, doneSignal)); executorService.submit(new exprotThread('E:/1.csv', recordList, doneSignal)); doneSignal.await(); System.out.println('Finish!!!'); } class exprotThread implements Runnable { private String filename; private List<Map<String, String>> list; private CountDownLatch countDownLatch; public exprotThread(String filename, List<Map<String, String>> list, CountDownLatch countDownLatch) { this.filename = filename; this.list = list; this.countDownLatch = countDownLatch; } @Override public void run() { try { CSVPrinter printer = new CSVPrinter(new FileWriter(filename), CSVFormat.EXCEL.withHeader('NAME', 'CODE')); for (Map<String, String> map : list) { printer.printRecord(map.values()); } printer.close(); countDownLatch.countDown(); } catch (IOException e) { e.printStackTrace(); } } }

CSV與EXCEL

/** * 測試寫100萬數據需要花費多長時間 */ @Test public void testMillion() throws Exception { int times = 10000 * 10; Object[] cells = {'滿100減15元', '100011', 15}; // 導出為CSV文件 long t1 = System.currentTimeMillis(); FileWriter writer = new FileWriter('G:/test1.csv'); CSVPrinter printer = CSVFormat.EXCEL.print(writer); for (int i = 0; i < times; i++) { printer.printRecord(cells); } printer.flush(); printer.close(); long t2 = System.currentTimeMillis(); System.out.println('CSV: ' + (t2 - t1)); // 導出為Excel文件 long t3 = System.currentTimeMillis(); XSSFWorkbook workbook = new XSSFWorkbook(); XSSFSheet sheet = workbook.createSheet(); for (int i = 0; i < times; i++) { XSSFRow row = sheet.createRow(i); for (int j = 0; j < cells.length; j++) { XSSFCell cell = row.createCell(j); cell.setCellValue(String.valueOf(cells[j])); } } FileOutputStream fos = new FileOutputStream('G:/test2.xlsx'); workbook.write(fos); fos.flush(); fos.close(); long t4 = System.currentTimeMillis(); System.out.println('Excel: ' + (t4 - t3)); }

Maven依賴

<dependencies> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-csv</artifactId> <version>1.5</version> </dependency> <dependency> <groupId>org.apache.poi</groupId> <artifactId>poi</artifactId> <version>3.17</version> </dependency> <dependency> <groupId>org.apache.poi</groupId> <artifactId>poi-ooxml</artifactId> <version>3.17</version> </dependency> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> </dependency></dependencies>

最后，剛才的例子中只寫了3個字段，100萬行，生成的CSV文件有十幾二十兆，太多的話建議分多個文件打包下周，不然想象一個打開一個幾百兆的excel都費勁。

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