1. 单元格类型

单元格的内容决定了单元格的类型，POI中定义的7种单元格类型：

1. 日期数据对应的单元格类型是CellType.NUMERIC，默认以浮点型数显示，显示为日期格式需要设置单元格样式DataFormat
2. 字符型单元格内容也可以为富文本RichTextString，可以对文本多部分设置字体Font

2. 错误单元格

Excel中存在错误单元格，在POI中是怎么表现的呢

org.apache.poi.ss.usermodel.FormulaError1

package org.apache.poi.ss.usermodel;  

import java.util.Map;  

import org.apache.poi.util.Internal;  

import java.util.HashMap;  

/** 
 * Enumerates error values in SpreadsheetML formula calculations. 
 *  
 * See also OOO's excelfileformat.pdf (2.5.6) 
 */  
public enum FormulaError {  
    @Internal  
    _NO_ERROR(-1, "(no error)"),  

    /** 
     * Intended to indicate when two areas are required to intersect, but do not. 
     * <p>Example: 
     * In the case of SUM(B1 C1), the space between B1 and C1 is treated as the binary 
     * intersection operator, when a comma was intended. end example] 
     * </p> 
     */  
    NULL(0x00, "#NULL!"),  

    /** 
     * Intended to indicate when any number, including zero, is divided by zero. 
     * Note: However, any error code divided by zero results in that error code. 
     */  
    DIV0(0x07, "#DIV/0!"),  

    /** 
     * Intended to indicate when an incompatible type argument is passed to a function, or 
     * an incompatible type operand is used with an operator. 
     * <p>Example: 
     * In the case of a function argument, text was expected, but a number was provided 
     * </p> 
     */  
    VALUE(0x0F, "#VALUE!"),  

    /** 
     * Intended to indicate when a cell reference is invalid. 
     * <p>Example: 
     * If a formula contains a reference to a cell, and then the row or column containing that cell is deleted, 
     * a #REF! error results. If a worksheet does not support 20,001 columns, 
     * OFFSET(A1,0,20000) will result in a #REF! error. 
     * </p> 
     */  
    REF(0x17, "#REF!"),  

    /** 
     * Intended to indicate when what looks like a name is used, but no such name has been defined. 
     * <p>Example: 
     * XYZ/3, where XYZ is not a defined name. Total is & A10, 
     * where neither Total nor is is a defined name. Presumably, "Total is " & A10 
     * was intended. SUM(A1C10), where the range A1:C10 was intended. 
     * </p> 
     */  
    NAME(0x1D, "#NAME?"),  

    /** 
     * Intended to indicate when an argument to a function has a compatible type, but has a 
     * value that is outside the domain over which that function is defined. (This is known as 
     * a domain error.) 
     * <p>Example: 
     * Certain calls to ASIN, ATANH, FACT, and SQRT might result in domain errors. 
     * </p> 
     * Intended to indicate that the result of a function cannot be represented in a value of 
     * the specified type, typically due to extreme magnitude. (This is known as a range 
     * error.) 
     * <p>Example: FACT(1000) might result in a range error. </p> 
     */  
    NUM(0x24, "#NUM!"),  

    /** 
     * Intended to indicate when a designated value is not available. 
     * <p>Example: 
     * Some functions, such as SUMX2MY2, perform a series of operations on corresponding 
     * elements in two arrays. If those arrays do not have the same number of elements, then 
     * for some elements in the longer array, there are no corresponding elements in the 
     * shorter one; that is, one or more values in the shorter array are not available. 
     * </p> 
     * This error value can be produced by calling the function NA 
     */  
    NA(0x2A, "#N/A"),  

    // These are POI-specific error codes  
    // It is desirable to make these (arbitrary) strings look clearly different from any other  
    // value expression that might appear in a formula.  In addition these error strings should  
    // look unlike the standard Excel errors.  Hence tilde ('~') was used.  

    /** 
     * POI specific code to indicate that there is a circular reference 
     *  in the formula 
     */  
    CIRCULAR_REF(0xFFFFFFC4, "~CIRCULAR~REF~"),  
    /** 
     * POI specific code to indicate that the funcition required is 
     *  not implemented in POI 
     */  
    FUNCTION_NOT_IMPLEMENTED(0xFFFFFFE2, "~FUNCTION~NOT~IMPLEMENTED~");  

    private final byte type;  
    private final int longType;  
    private final String repr;  

    private FormulaError(int type, String repr) {  
        this.type = (byte)type;  
        this.longType = type;  
        this.repr = repr;  
    }  

    /** 
     * @return numeric code of the error 
     */  
    public byte getCode() {  
        return type;  
    }  
    /** 
     * @return long (internal) numeric code of the error 
     */  
    public int getLongCode() {  
        return longType;  
    }  

    /** 
     * @return string representation of the error 
     */  
    public String getString() {  
        return repr;  
    }  

    private static final Map<String, FormulaError> smap = new HashMap<String, FormulaError>();  
    private static final Map<Byte, FormulaError> bmap = new HashMap<Byte, FormulaError>();  
    private static final Map<Integer, FormulaError> imap = new HashMap<Integer, FormulaError>();  
    static{  
        for (FormulaError error : values()) {  
            bmap.put(error.getCode(), error);  
            imap.put(error.getLongCode(), error);  
            smap.put(error.getString(), error);  
        }  
    }  

    public static final boolean isValidCode(int errorCode) {  
        for (FormulaError error : values()) {  
            if (error.getCode() == errorCode) return true;  
            if (error.getLongCode() == errorCode) return true;  
        }  
        return false;  
    }  

    public static FormulaError forInt(byte type) throws IllegalArgumentException {  
        FormulaError err = bmap.get(type);  
        if(err == null) throw new IllegalArgumentException("Unknown error type: " + type);  
        return err;  
    }  
    public static FormulaError forInt(int type) throws IllegalArgumentException {  
        FormulaError err = imap.get(type);  
        if(err == null) err = bmap.get((byte)type);  
        if(err == null) throw new IllegalArgumentException("Unknown error type: " + type);  
        return err;  
    }  

    public static FormulaError forString(String code) throws IllegalArgumentException {  
        FormulaError err = smap.get(code);  
        if(err == null) throw new IllegalArgumentException("Unknown error code: " + code);  
        return err;  
    }  
}

3. 实例

package hssf.sheet.cell;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Calendar;
import java.util.Date;

import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.CellType;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;

public class ExportDataCell {

    public static void main(String[] args) throws Exception {
        File file = new File("C:\\Users\\Administrator\\Desktop\\test.xls");
        if (file.exists()) {
            file.delete();
        }
        BufferedOutputStream out = null;
        try {
            out = new BufferedOutputStream(new FileOutputStream("C:\\Users\\Administrator\\Desktop\\test.xls"));
            exportExcel(out);
        } finally {
            out.close();
        }
    }

    private static void exportExcel(BufferedOutputStream out) throws IOException {
        Workbook wb = new HSSFWorkbook();
        //Workbook wb = new XSSFWorkbook();
        Sheet sheet = wb.createSheet("各种类型单元格");

        sheet.createRow(0).createCell(0).setCellValue(1.1);
        sheet.createRow(1).createCell(0).setCellValue(new Date());
        sheet.createRow(2).createCell(0).setCellValue(Calendar.getInstance());
        sheet.createRow(3).createCell(0).setCellValue("字符串");
        sheet.createRow(4).createCell(0).setCellValue(true);
        sheet.createRow(5).createCell(0).setCellType(CellType.ERROR);

        wb.write(out);
    }
}