我有一个Java类，我使用它来根据输入在特定单元格中写入特定字符串。
我使用Apache POI。
我的类有两个写入方法。一个用于单行写入，另一个用于多次写入。
多次写入的方法似乎是我的问题，我认为 :(
这是我的写入类：
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Iterator;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.CellType;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.xssf.usermodel.XSSFRow;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
public class TrueExcelWriter {
    
    public TrueExcelWriter(){}
    private static int findRow(XSSFSheet sheet, String cellContent) {
        for (Row row : sheet) {
            for (Cell cell : row) {
                if (cell.getCellType() == CellType.STRING) {
                    if (cell.getRichStringCellValue().getString().trim().equals(cellContent)) {
                        return row.getRowNum();  
                    }
                }
                    
                if (cell.getCellType().equals(CellType.NUMERIC)){
                    long lookup = (long) cell.getNumericCellValue();
                    String catcher = Long.toString(lookup);
                        
                    if(catcher.equals(cellContent)){
                        return row.getRowNum();
                    }
                }
                    
            }
        }               
        return 0;
    }
    
    public void WriteToAll(String suchobjekt, String ID, String SPID) throws FileNotFoundException, IOException{
    
        final String fileName = "C:/Temp/TTT.xlsx";
        InputStream input = new FileInputStream(fileName);
        
        XSSFWorkbook wb = new XSSFWorkbook(input);
        XSSFSheet sheet = wb.getSheetAt(0);
        
        int colnr = 0; 
        
        switch (suchobjekt) {
            case "option1":
                colnr = 15; 
                break;
             case "option2":
                colnr = 16; 
                break;
            case "option3":
                colnr = 999; 
                break;
        }
        
        Iterator<Row> iterator = sheet.iterator();
        
        while (iterator.hasNext()) {
            Row nextRow = iterator.next();
            
            if(nextRow.getRowNum()==0){ 
            continue; //just skip the rows if row number is X or Y
            }
            
            Iterator<Cell> cellIterator = nextRow.cellIterator();
            while (cellIterator.hasNext()) {
                Cell nextCell = cellIterator.next();
                
                String y = nextCell + "";
                
                if(y.equals(ID)){
                    
                    Row r = sheet.getRow(nextRow.getRowNum());
                    if (r == null) {
                        r = sheet.createRow(nextRow.getRowNum());
                    }
                    
                    Cell c = r.getCell(colnr);
                    if (c == null) {
                        c = r.createCell(colnr, CellType.STRING);
                    }
                    c.setCellValue(SPID);
                    
                }
                
            }
            
        }
        
        input.close();
        OutputStream output = new FileOutputStream(fileName);
        wb.write(output);
        output.close();
        wb.close();
        
    }
 
    public void WriteTo(String suchobjekt, String ID, String SPID) throws FileNotFoundException, IOException{
    
        final String fileName = "C:/Temp/TTT.xlsx";
        InputStream input = new FileInputStream(fileName);
        
        XSSFWorkbook wb = new XSSFWorkbook(input);
        XSSFSheet sheet = wb.getSheetAt(0);
        
        int colnr = 0;
        int rownr;
        
        switch (suchobjekt) {
            case "option1":
                colnr = 15; 
                break;
             case "option2":
                colnr = 16; 
                break;
            case "option3":
                colnr = 999; 
                break;
        }
        
        rownr = findRow(sheet, ID);
        
        Row r = sheet.getRow(rownr);
        if (r == null) {
            r = sheet.createRow(rownr);
        }
        
        Cell c = r.getCell(colnr); 
        if (c == null) {
            c = r.createCell(colnr, CellType.STRING);
        }
        c.setCellValue(SPID);
        
        input.close();
        OutputStream output = new FileOutputStream(fileName);
        wb.write(output);
        output.close();
        wb.close();
    
    }
}

try {
    ter.WriteToAll("option2", "abc", "done");
} catch (IOException ex) {
    System.out.println("Error! "+ex);
}

...14   15    16   ...
  ... | ID  | ...
  ... | abc | done
  ... | abc | done
  ... | abc | done
  ... | def | 
  ... | ghi | 
  ... | jkl | 
  ... | jkl | 
  ... | jkl | 
  ... | mno | 
  ... | mno | 
  ... | mno | 

Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException
	at java.base/java.util.TreeMap$PrivateEntryIterator.nextEntry(TreeMap.java:1208)
	at java.base/java.util.TreeMap$ValueIterator.next(TreeMap.java:1253)
	at easypackaging.TrueExcelWriter.WriteToAll(TrueExcelWriter.java:88)
	at easypackaging.TEST_TrueVerladen.actionPerformed(TEST_TrueVerladen.java:172)
	at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1967)
	at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2308)
	at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
	at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
	at java.desktop/javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:279)
	at java.desktop/java.awt.Component.processMouseEvent(Component.java:6636)
	at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3342)
	at java.desktop/java.awt.Component.processEvent(Component.java:6401)
	at java.desktop/java.awt.Container.processEvent(Container.java:2263)
	at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5012)
	at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2321)
	at java.desktop/java.awt.Component.dispatchEvent(Component.java:4844)
	at java.desktop/java.awt.LightweightDispatcher.retarget
<details>
<summary>英文:</summary>
I have a java class which I use to write a specific String in a specific cell, depending on the input.
I use Apache POI.
My Class has two writing methods. One for single line writing and one for writing multiple times.
The method for multiple writing seems to be my trouble, I think :(
here is my writing class:

public TrueExcelWriter(){}
private static int findRow(XSSFSheet sheet, String cellContent) {
for (Row row : sheet) {
for (Cell cell : row) {
if (cell.getCellType() == CellType.STRING) {
if (cell.getRichStringCellValue().getString().trim().equals(cellContent)) {
return row.getRowNum();  
}
}
if (cell.getCellType().equals(CellType.NUMERIC)){

                    if(catcher.equals(cellContent)){
return row.getRowNum();
}

            }
}
}               
return 0;
}
public void WriteToAll(String suchobjekt, String ID, String SPID) throws FileNotFoundException, IOException{
final String fileName = "C:/Temp/TTT.xlsx";
InputStream input = new FileInputStream(fileName);
XSSFWorkbook wb = new XSSFWorkbook(input);
XSSFSheet sheet = wb.getSheetAt(0);
int colnr = 0; 
switch (suchobjekt) {
case "option1":
colnr = 15; 
break;
case "option2":
colnr = 16; 
break;
case "option3":
colnr = 999; 
break;
}
Iterator<Row> iterator = sheet.iterator();
while (iterator.hasNext()) {
Row nextRow = iterator.next();
if(nextRow.getRowNum()==0){ 
continue; //just skip the rows if row number is X or Y
}
Iterator<Cell> cellIterator = nextRow.cellIterator();
while (cellIterator.hasNext()) {
Cell nextCell = cellIterator.next();
String y = nextCell + "";
if(y.equals(ID)){
Row r = sheet.getRow(nextRow.getRowNum());
if (r == null) {
// First cell in the row, create
r = sheet.createRow(nextRow.getRowNum());
}
Cell c = r.getCell(colnr);
if (c == null) {
// New cell
c = r.createCell(colnr, CellType.STRING);
}
c.setCellValue(SPID);
}
}
}
input.close();
OutputStream output = new FileOutputStream(fileName);
wb.write(output);
output.close();
wb.close();
}
public void WriteTo(String suchobjekt, String ID, String SPID) throws FileNotFoundException, IOException{
final String fileName = "C:/Temp/TTT.xlsx";
InputStream input = new FileInputStream(fileName);
XSSFWorkbook wb = new XSSFWorkbook(input);
XSSFSheet sheet = wb.getSheetAt(0);
int colnr = 0;
int rownr;
switch (suchobjekt) {
case "option1":
colnr = 15; 
break;
case "option2":
colnr = 16; 
break;
case "option3":
colnr = 999; 
break;
}
rownr = findRow(sheet, ID);
Row r = sheet.getRow(rownr);
if (r == null) {
// First cell in the row, create
r = sheet.createRow(rownr);
}
Cell c = r.getCell(colnr); 
if (c == null) {
// New cell
c = r.createCell(colnr, CellType.STRING);
}
c.setCellValue(SPID);
input.close();
OutputStream output = new FileOutputStream(fileName);
wb.write(output);
output.close();
wb.close();
}

I am using the following code to write something in my excel file:

My excel file currently looks like this:

If I use the method from above and used it for all IDs, everything works **except** for ID "***def***"!
I don't know why this does not work for this single one. :(
If I try the single line writing function for this ID, it works.
But I font know why the multiple writing function does not work for this one.
I am getting the following error message:

`TrueExcelWriter` is the class where I run the `ter.WriteToAll`.
I googled the error but I was not able to solve my problem with what I found. :(
If needed, I can upload my complete (censored) excel sheet for you.
Can you guys help me out? 
Sincerely yours,
Shathos
**UPDATE:**
I wrote a new, simpler algorithm for my multiple line writing which worked for me. :) Thank's for the help!
New function:

    final String fileName = "C:/Temp/TTT.xlsx";
InputStream input = new FileInputStream(fileName);
XSSFWorkbook wb = new XSSFWorkbook(input);
CreationHelper createHelper = wb.getCreationHelper();
XSSFSheet sheet = wb.getSheetAt(0);
XSSFCell cell;
XSSFRow row;
int colnr = 15;
int rownr = 0;
rownr = findRow(sheet, ID);
for(int i = rownr; i < sheet.getLastRowNum(); i++){
row = sheet.getRow(i);
String y = row.getCell(colnr)+"";
if(y.equals(ID)){
row.createCell(16).setCellValue(createHelper.createRichTextString(SPID));
}
}
input.close();
OutputStream output = new FileOutputStream(fileName);
wb.write(output);
output.close();
wb.close();
}

</details>
# 答案1
**得分**: 1
你在遍历行时添加行来修改表格，这就是导致ConcurrentModificationException异常的原因。
<details>
<summary>英文:</summary>
You are modifying the sheet by adding rows while iterating over the rows. That is where the ConcurrentModificationException is coming from.
</details>