Excel file reading and writing (creation and parsing)

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Can be done Excel The mainstream technologies of document processing include ：

① Apache POI ( be based on DOM The way to analyze , Load the file directly into memory , Faster , fit Excel Application scenarios with a small amount of file data )

② JXL ( fit Excel Application scenarios with a small amount of file data )

③ Alibaba EasyExcel ( Adopt the parsing mode of line by line reading , Notify the processing of the parsing result of each line in the observer mode (AnalysisEventListener), Therefore, it is more suitable for those with a large amount of data Excel File parsing )
( One of the most common is Apache POI,Alibaba EasyExcel.)

One .Apache POI

POI Provides parsing of files in different formats ：
HSSF Used to parse the old version Excel file (.xls), Because of the old version of Excel Files can only exist 65535 Row data , So it's not often used , It is commonly used at present XSSF analysis Excel file (.xlsx).

First add jjar Packet dependency ：

1. Workbook
Workbook The interface represents a Excel file , Usually create its implementation class object to create (/ load )Excel file , Common implementation classes are XSSFWorkbook.

(1). establish Excel file

try (Workbook workbook = new XSSFWorkbook();
				FileOutputStream out =
						new FileOutputStream("E:\\ The ape \\demo.xlsx")) {
			
			//  take  workbook  The data contained in the object , Through output stream , Write to Excel file 
			workbook.write(out);
			} catch (IOException e) {
			e.printStackTrace();
		}
		

(2). load ( analysis )Excel file

        //  Through the input stream , Read excel file 
		FileInputStream in = new FileInputStream("E:\\ achievement .xlsx");
		//  Pass the input stream into Workbook
		Workbook workbook = new XSSFWorkbook(in);
		

Note that the input stream is also closed , You can call in.close(), We usually use try catch Block to automatically close ：

try (Workbook workbook = new XSSFWorkbook();
				FileOutputStream out =
						new FileOutputStream("E:\\demo.xlsx")) {
			//  take  workbook  The data contained in the object , Through output stream , Write to Excel file 
			workbook.write(out);
		} catch (IOException e) {
			e.printStackTrace();
		}

（3）sheet ( workbook )
adopt Workbook To carry out the workbook sheet Creation and acquisition of
①.sheet The creation of

//  Create Workbook with default name 
Sheet sheet1 = workbook.createSheet();

//  Create a workbook with a custom name 
Sheet sheet2 = workbook.createSheet(" Customize Workbook ");

②.sheet Acquisition

//  Get by workbook subscript Sheet
Sheet sheet01 = workbook.getSheetAt(0);

//  Get by workbook name Sheet
Sheet sheet02 = workbook.getSheet("Sheet0");

③. Number of workbooks

int sheetNum = workbook.getNumberOfSheets();
System.out.println(" Number of workbooks ：" + sheetNum);

④. Data row of workbook

 System.out.println(" workbook 0 The data line ：" + sheet0.getLastRowNum());

(3).Row( data row )
①. Create data rows

Row row0 = sheet0.createSheet(0);

②. Get first / Last line subscript

int first = sheet.getFirstRowNum();
int last = sheet.getLastRowNum();

③. Get the specified line according to the subscript

Row row = sheet.getRow(0); // first line 

④. Traverse the specified area row

//  Traverse all lines 
for (int i = 1; i <= sheet.getLastRowNum(); i++) {
    Row row = sheet.getRow(i);
    System.out.println(row);
}

(4).Cell( Cell )
①. Creation and acquisition of cells

Cell cell0 = Row.createCell(0); // cell The creation of 
Cell cell = Row.getCell(0); // cell Acquisition 

②. Set column header ( The first line of the form ) The content of

cellHead.setCellValue(" Serial number ");
cellHead1.setCellValue(" full name ");
cellHead2.setCellValue(" Gender ");
cellHead3.setCellValue(" Date of creation ");

②. Get cell contents

System.out.println(" Serial number ：" + cell0.getNumericCellValue());
System.out.println(" full name ：" + cell1.getStringCellValue());	

③. Set cell contents

cell0.setCellValue(Math.random()*1000);		

④. Get cell type

CellType type = cell.getCellType();

⑤. Format cell

     //  Create cell format 
     //  Get format encoding 
      DataFormat dataFormat = workbook.createDataFormat();
      short formatCode = dataFormat.getFormat("yyyy-MM-dd HH:mm:ss");
	  System.out.println(" Cell format encoding ：" + formatCode);
	
	 //  establish cellStyle Cell format object 
	  CellStyle cellStyle = workbook.createCellStyle();
	  cellStyle.setDataFormat(formatCode); //  Set cell format encoding 
      ...
     //  By setting cellStyle Cell format object , To display the date normally 
      Cell cell0 = Row.createCell();
	  cell0.setCellStyle(cellStyle); //  Format cell 
	  cell0.setCellValue(new Date());	 //  Save date to this cell 

Two . Super large Excel Reading and writing of documents

1. Use POI write in ===> SXXSFWorkbook

It can write a very large amount of data , Such as 100w Even more , Write data fast , Less memory .
It will generate temporary files during writing , The default is 100 Pieces of data are saved to memory , If the default data amount is exceeded , The previous data will be written to the temporary file , By setting SXSSFWorkbook To set the number of rows held in memory each time , When this value is reached , I'll take the data flush To disk , In this way, there will not be insufficient memory .

SXSSFWorkbook write in 10w Row data ( Because of the time problem, use 10w Line data to test )
The implementation code is as follows ：

//  Workbook Implementation class of  SXSSFWorkbook:
		try (Workbook workbook = new SXSSFWorkbook();
				FileOutputStream out = new FileOutputStream("E:\\10w.xlsx")) {
			long begin = System.currentTimeMillis(); 
			Sheet sheet = workbook.createSheet();
			
			//  Create column header 
			Row headRow = sheet.createRow(0);
		    //  Set column header cell content 
			Cell cellVal0 = headRow.createCell(0);
			cellVal0.setCellValue(" Serial number ");
			
			//  Create data rows 
			for(int i = 0;i < 100000;i++) {
				String name = "A"  + i;
				//  Create lines 
				Row row = sheet.createRow(i+1);
				
				//  Create cells 
				Cell cell0 = row.createCell(0); //  Serial number 
				cell0.setCellValue(String.valueOf(i+1));
			}	
		workbook.write(out);
		long after = System.currentTimeMillis();  
System.out.println("SXSSFWorkbook write in 10w Time consuming for row data ：" + (after-begin) + "ms");
		
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

The operation results are as follows ：

CPU Use as follows

2. Use Alibaba EasyExcel write in
First download Alibaba EasyExcel relevant jar package

Use EasyExcel write in 10w Order data

// easyExcel: It is fast to read large files , Memory usage is small 
//  write in 10w Order data 
		long begin = System.currentTimeMillis();
		// 10w
		EasyExcel.write("E:\\easy10w.xlsx",Order.class).sheet(" Order list ").doWrite(data());
	
		long after = System.currentTimeMillis();
		System.out.println(" Total time consuming " + (after-begin) + "ms");
	
	}
	//  establish 100w Order data 
	private static List<Order> data(){
		List<Order> list = new ArrayList<Order>();
		
		for(int i = 0;i < 100000;i++) {
			list.add(new Order());
			}
		return list;
		}

The operation results are as follows ：

CPU The usage rate is as follows ：

thus it can be seen ,10w The data of , by comparison ,SXSSFWorkbook The fastest ,CPU The highest occupancy rate ;EasyExcel Low running speed ,CPU The lowest occupancy . because poi Memory consumption is very high ,EasyExcel It can greatly reduce the occupation of memory ( as a result of EasyExcel Adopt the parsing mode of line by line reading , Not all file data is loaded into memory at one time , Is to read data line by line on the disk ), Therefore, it is recommended to use EasyExcel.

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