将数据库中的数据导入到excel中

        从数据库中读取数据导入到excel中，如果数据量小，的确很简单，直接用POI输出就OK了，可是我这边有＞6W的数据要输出，java运行了直接溢出了，于是前辈给了个取巧的办法，调用java命令并设置vm参数-Xms1024M -Xmx1024M，呵呵，这样很大了，那么下面就是着手运行这个命令就行了，首先把这个导出的方法写在要调用的类的main方法中，然后在我的网站应用的Action中去执行一个命令脚本，windows下用bat，linux下用sh，由于要执行脚本，在linux下要注意就是要把你的应用读写权限打开。那么先从调用的命令开始
    1.设置好参数，就是main中的String[] args参数比如输出excel的路径
                String excelPath = Struts2Utils.getSession().getServletContext().getRealPath("/upload/doc/export.xls");
    2.生成好bat或者是sh文件
                String osName = System.getProperty("os.name");//获取操作系统
                if (osName.toLowerCase().indexOf("windows") != -1) {
                        filePath = Struts2Utils.getSession().getServletContext().getRealPath("/WEB-INF/classes/excelDb.bat");
                } 
                else
               {
                       filePath = Struts2Utils.getSession().getServletContext().getRealPath("/WEB-INF/classes/excelDb.sh");
               }

              String cmdLine ="";
              cmdLine+="cd "+classPath+" \r\n";
              cmdLine+=" java -Xms1024M -Xmx1024M -Djava.ext.dirs="+dirPath+" com.twc.common.utils.command.Command "+excelPath；
              try {
                       FileUtils.writeFile(new File(filePath), cmdLine.getBytes());//生成文件
              } catch (IOException e1) {
                   e1.printStackTrace();
              }
    3.调用这个bat或者是sh文件
      

        Process proc = null;
        try {
                 String result = "";
                 proc = Runtime.getRuntime().exec(filePath);
                 BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(proc.getInputStream()));
                 while ((result = bufferedReader.readLine()) != null)
                 System.out.println(result);

                 if(proc.waitFor() != 0) {
                            logger.error("Can't execute: " + cmdLine);
                 }
                if(error.length() > 0) {
                            logger.warn(error);
                 }
        } catch (Exception e) {
                            logger.error(e.getMessage(), e);
        } finally {
                            proc.destroy();
                            proc = null;
        }

这样Action的使命就完成了，那么接下来就是实现调用类的导出excel方法了(我的调用类是Command类)下面的方法是main中的，我截取了最重要的出来

 1 List<Vector> result = new ArrayList<Vector>();
 2             dba.open();
 3             try {
 4             
 5                 String sql = sb.toString();
 6                 String[] arrFields = fields.split(",");
 7                 int size = arrFields.length;
 8                 dba.query(sql);
 9                 while (dba.rs != null && dba.rs.next()) {
10             
11                     Vector cell = new Vector();
12                     for(int i=1;i<size+1;i++)
13                     {
14                         cell.add(dba.rs.getString(i));
15                     }
16                     result.add(cell);
17                 }//从数据库的到数据存放在result中
18             } catch (SQLException e) {
19                 
20             }
21             PoiUtils e  =   new  PoiUtils(excelPath);
22             int cnt=1;
23             int size = result.size();
24             int block = size/Command.BLOCK;
25             if(block<1)//判断数据是否超出excel极限（excel的一个sheet最多存放6w多行数据)
26             {
27                 //直接把所有数据输出到一个sheet中去
28                 e.createSheet(0);
29                 e.createRow(0);
30                 for(int j=0;j<arrField.length;j++)
31                 {
32                     
33                         e.setCell(j, arrField[j]);
34                     
35                 }
36                 for(int l=1;l<size+1;l++)    
37                 {        e.createRow(l);
38                         for(int j=0;j<arrField.length;j++)
39                         {
40                             if(result.get(l-1).get(j)!=null)
41                             {
42                                 e.setCell(j, result.get(l-1).get(j).toString());
43                             }
44                             else
45                             {
46                                 e.setCell(j, "");
47                             }
48                         }
49                 }
50             }
51             else
52             {
53                 //如果超出了范围则把数据分别输出到k个sheet中去
54                 for(int k=0;k<block;k++)
55                 {
56                     //第k+1个sheet
57                     e.createSheet(k+1);
58                     //数据字段名
59                     e.createRow(0);
60                     for(int j=0;j<arrField.length;j++)
61                     {
62                         
63                             e.setCell(j, arrField[j]);
64                         
65                     }
66                     int start = k*Command.BLOCK;
67                     int end = Command.BLOCK*(k+1);
68                     for(int l=start;l<end;l++)    //输出到excel中
69                     {        
70                             e.createRow(cnt);
71                             cnt++;
72                             if(cnt==Command.BLOCK+1)cnt = 1;
73                             for(int j=0;j<arrField.length;j++)
74                             {
75                                 if(result.get(l).get(j)!=null)
76                                 {
77                                     e.setCell(j, result.get(l).get(j).toString());
78                                 }
79                                 else
80                                 {
81                                     e.setCell(j, "");
82                                 }
83                             }
84                     }
85                 }
86             }
87             
88              try    {
89                     e.exportXLS();//输出结果
90                     System.out.println("Exprot Success!");
91                 }   catch  (XLSException e1)   {
92                 
93                 }