struts图片显示控制

<img   src='E.do'> </img>

这样放在网页里图片会页面加载就会显示
我们要做一个效果为需要显示图片的时候才去显示
要求很简单，但是实现起来却没那么容易
需要注意的是：图片为在数据库中读取出来且未保存在硬盘中，src为.do，所以就不能用id.src=''的方式改变src，也不能用id.style.visibility='hidden'; 或者id.style.display='none'; 来隐藏实现，况且这样也不是业务所要求的，要求就是选择一个种类再去显示这个种类的图片

好，下面说实现办法

用到的标签为

<logic:present name="tianjin">
  </logic:present>

解释一下这个标签

<logic:present name="tianjin">
如果在你的action中设置了tianjin就执行到这儿。如：request.setAttribute("tianjin","天津")或session.setAttribute("tianjin","天津")
<bean:write name="tianjin"/>
</logic:present> 跟这个标签差不多的有个<logic:equal>
<logic:equal name="tianjinForm" property="tianjinAction" value="tianjin">
如果tianjinForm里的属性tianjinAction的值等于tianjin就执行这儿。
</logic:equal>

下边把代码帖上（部分）

<html:form action="/EnrolRushRedLightManageInfo.do" method="post">
    图片路径：<html:select property="enrolRushRedLightPhotoManagePhotoPath" οnclick="enrolRushRedLightPhotoManagePhotoDisplay()">
    <html:option value=""></html:option>
    <html:option value="齐齐哈尔">齐齐哈尔</html:option>
    <html:option value="齐齐哈尔">天津</html:option>
    </html:select>
<logic:present name="tianjin">
     <img src="EnrolRushRedLightPhotoManagePhotoDisplay.do"></img>
  </logic:present>

<script language="javascript" type="text/javascript">
function enrolRushRedLightPhotoManagePhotoDisplay()
{
 document.forms[0].action='EnrolRushRedLightPhotoManagePhotoDisplay.do' ;
 document.forms[0].submit();
}
</script>

 action(半成品，但可通过）

public class EnrolRushRedLightPhotoManagePhotoDisplayAction extends Action 
{
    public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request,HttpServletResponse response) 
 {
  EnrolRushRedLightPhotoManagePhotoDisplayForm enrolRushRedLightPhotoManagePhotoDisplayForm = new EnrolRushRedLightPhotoManagePhotoDisplayForm();
  String enrolRushRedLightPhotoManagePhotoPath = enrolRushRedLightPhotoManagePhotoDisplayForm.getEnrolRushRedLightPhotoManagePhotoPath() ;
  
  @SuppressWarnings("unused")
  String qiqihaerSQL ;
  @SuppressWarnings("unused")
  String tianjinSQL ;
  
  HttpSession session = request.getSession() ;
  if(enrolRushRedLightPhotoManagePhotoPath.equals("齐齐哈尔"))
  {
   //查询齐齐哈尔的图片
   qiqihaerSQL = "查询齐齐哈尔的SQL语句" ;
   session.setAttribute("qiqihaer", "qiqihaerSQL") ;
  }
  if(enrolRushRedLightPhotoManagePhotoPath.equals("天津"))
  {
   //查询天津的图片
   tianjinSQL = "查询天津的SQL语句" ;
   session.setAttribute("tianjin", "tianjinSQL") ;
  }
  @SuppressWarnings("unused")
  String SQL = (String)session.getAttribute("tianjin") ;
  Connection conn = null;
  Statement stmt = null;
  BufferedInputStream inputimage=null;
  DataBaseConnection dbc = new DataBaseConnection() ;
  ResultSet rs = null ;
  try 
  {
   try 
   {
    conn = dbc.getConnection();
    stmt = conn.createStatement();    
    boolean defaultCommit = conn.getAutoCommit();
    conn.setAutoCommit(false);
    //在下面括号里换上SQL变为动态SQL语句
    rs = stmt.executeQuery("SELECT img FROM dzjc_img");
    while (rs.next()) 
    {
        Blob blob = (Blob)rs.getBlob("img");
        inputimage = new BufferedInputStream(blob.getBinaryStream());
    }
    conn.setAutoCommit(defaultCommit);
   } 
   catch (SQLException e) 
   {
    e.printStackTrace();
    System.out.println("blobRead()'s exception"+e);
    try 
    {
     conn.rollback();
     throw e;
    }
    catch (SQLException e1)
    {
     e1.printStackTrace();
    }
   }
  }
  catch (Exception e1)
  {
   e1.printStackTrace();
  }
  BufferedImage image = null;
  try
  {
   image = ImageIO.read(inputimage);
   ServletOutputStream sos = response.getOutputStream();
   ImageIO.write(image, "jpg", sos);
   JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(sos);
   encoder.encode(image);
   inputimage.close();
   sos.flush();
  }
  catch(Exception e)
  {
   System.out.println(e);
  }
  return mapping.findForward("abc");
 }
}

 form

package struts.form;
import java.util.List;
import javax.servlet.http.HttpServletRequest;
import org.apache.struts.action.ActionErrors;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.upload.FormFile;
public class EnrolRushRedLightPhotoManagePhotoDisplayForm extends ActionForm { 
 private static final long serialVersionUID = 1L;
 private FormFile errorRushRedLightPhotoManagePhotoDisplayPhoto; 
 private String enrolRushRedLightPhotoManagePhotoPath ;
 private List errors ;
 public void setErrors(List errors)
 {
  this.errors = errors ;
 }
 public List getErrors()
 {
  return this.errors ;
 }
 public ActionErrors validate(ActionMapping mapping,
   HttpServletRequest request) {
  ActionErrors errors = new ActionErrors() ;
  // 判断用户是否登陆，没有的话返回到登陆页面
  if (request.getSession().getAttribute("sessionUserName")==null||"".equals(request.getSession().getAttribute("sessionUserName"))) 
     {
   mapping.findForward("sessionEnded") ;//mapping是转发到页面的，不是提交
     }
  else
  {
  }
  return  errors;
 }
 public void reset(ActionMapping mapping, HttpServletRequest request) {
 }
 public FormFile getErrorRushRedLightPhotoManagePhotoDisplayPhoto() {
  return errorRushRedLightPhotoManagePhotoDisplayPhoto;
 }
 public void setErrorRushRedLightPhotoManagePhotoDisplayPhoto(
   FormFile errorRushRedLightPhotoManagePhotoDisplayPhoto) {
  this.errorRushRedLightPhotoManagePhotoDisplayPhoto = errorRushRedLightPhotoManagePhotoDisplayPhoto;
 }
 public String getEnrolRushRedLightPhotoManagePhotoPath() {
  return enrolRushRedLightPhotoManagePhotoPath;
 }
 public void setEnrolRushRedLightPhotoManagePhotoPath(
   String enrolRushRedLightPhotoManagePhotoPath) {
  this.enrolRushRedLightPhotoManagePhotoPath = enrolRushRedLightPhotoManagePhotoPath;
 }
}