如题，代码如下：[code="java"]package test;

import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.List;
import javax.servlet.*;

import jxl.Workbook;
import jxl.write.Label;
import jxl.write.WritableCellFormat;
import jxl.write.WritableFont;
import jxl.write.WritableSheet;
import jxl.write.WritableWorkbook;

public class TestExcel {
private String driverClass = "net.sourceforge.jtds.jdbc.Driver";

private String url ="jdbc:jtds:sqlserver:/localhost:1433/demo";

private String user = "sa";

private String password = "";

private Connection connection;
public void exportClassroom(OutputStream os) {  

    try {  
    WritableWorkbook wbook = Workbook.createWorkbook(os); //建立excel文件  
    WritableSheet wsheet = wbook.createSheet("报警记录表", 0); //工作表名称  
    //设置Excel字体  
    WritableFont wfont = new WritableFont(WritableFont.ARIAL, 16,  
    WritableFont.BOLD, false,  
    jxl.format.UnderlineStyle.NO_UNDERLINE,  
    jxl.format.Colour.BLACK);  
    WritableCellFormat titleFormat = new WritableCellFormat(wfont);  
    String[] title = { "报警记录编号", "报警时间", "报警设备", "报警设备编号","报警事件名称","报警编号"};  
    //设置Excel表头  
    for (int i = 0; i < title.length; i++) {  
    Label excelTitle = new Label(i, 0, title[i], titleFormat);  
    wsheet.addCell(excelTitle);  
    }  
    int c = 1; //用于循环时Excel的行号  
    Connection con=openConnection();
    Statement st=con.createStatement();
    String sql="select * from jlbjsj where BJJLSJ between '2010-09-01 08:19:25' and '2010-12-02 08:19:25' and BJSBMC like '%'";
    ResultSet rs=st.executeQuery(sql); //这个是从数据库中取得要导出的数据  
    while (rs.next()){
        Label content1 = new Label(0, c, (String)rs.getString("BJJLBH"));  
        Label content2 = new Label(1, c, (String)rs.getString("BJJLSJ"));  
        Label content3 = new Label(2, c, (String)rs.getString("BJSBMC"));   
        Label content4 = new Label(3, c, (String)rs.getString("BJSBBH"));
        Label content5 = new Label(4, c, (String)rs.getString("BJBLMC"));
        Label content6 = new Label(5, c, (String)rs.getString("BJBLBH"));
        //Label content7 = new Label(3, c, (String)rs.getString("BJSBBH"));
        wsheet.addCell(content1);  
        wsheet.addCell(content2);  
        wsheet.addCell(content3);  
        wsheet.addCell(content4);
        wsheet.addCell(content5);
        wsheet.addCell(content6);
        c++;  
    }  
    wbook.write(); //写入文件  
    wbook.close();  
    os.close(); 
    System.out.println("导入成功！");
    } catch (Exception e) {  

    e.printStackTrace(); 

    }  

    }
public Connection openConnection() throws SQLException {
    try {
        Class.forName(driverClass).newInstance();
        connection = DriverManager.getConnection(url, user, password); 
        return connection;
    } catch (Exception e) {
        throw new SQLException(e.getMessage());
    }
}
public void closeConnection() {
    try {        
        if (connection != null)
            connection.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}
public static void main(String[] args){
    TestExcel te=new TestExcel();
    File f=new File("c:\\kk.xls");
    try{
        f.createNewFile();
        OutputStream os=new FileOutputStream(f);
        te.exportClassroom(os);
    }catch(Exception e){
        e.printStackTrace();
    }

}

}
[/code]

文件下载例子：
[url]
http://yaofeng911.iteye.com/blog/472492
[/url]

把相应的流、文件替换成你的就OK了

[code="java"]

File f=new File("c:\kk.xls");

try{

f.createNewFile();

OutputStream os=new FileOutputStream(f);

te.exportClassroom(os);

}catch(Exception e){

e.printStackTrace();

}

[/code]

你自己写的代码，你是用File来构建OutputStream的 你说它最后写入到哪里去了？
c:/kk.xls啊 如果你的项目发布到了服务器上，那就在服务器的C盘 你想弄到本地的话你就别写入文件，用装载了数据的流传输给客户端，让客户保存，即可弄到本地（相当于文件下载）

导出excel文件，可以用PageOffice插件的。