Struts2中，采用注解的方式配置json，总是异常

import java.awt.Image;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import javax.imageio.ImageIO;import net.fckeditor.handlers.PropertiesLoader;import net.fckeditor.jackie.util.FileUtil;import org.apache.struts2.ServletActionContext;import org.apache.struts2.convention.annotation.Action;import org.apache.struts2.convention.annotation.ParentPackage;import org.apache.struts2.convention.annotation.Result;@SuppressWarnings("serial")@ParentPackage("json-default")public class ImageUploadAction extends BaseAction{    private File    file;    private String    fileFileName;    private String    fileFileContentType;    private String    message    = "你已成功上传文件";    private Integer    width    = 0;    private Integer    height    = 0;        public File getFile()    {        return file;    }        public void setFile(File file)    {        this.file = file;    }        public String getFileFileName()    {        return fileFileName;    }        public void setFileFileName(String fileFileName)    {        this.fileFileName = fileFileName;    }        public String getFileFileContentType()    {        return fileFileContentType;    }        public void setFileFileContentType(String fileFileContentType)    {        this.fileFileContentType = fileFileContentType;    }        public String getMessage()    {        return message;    }        public void setMessage(String message)    {        this.message = message;    }        public Integer getWidth()    {        return width;    }        public void setWidth(Integer width)    {        this.width = width;    }        public Integer getHeight()    {        return height;    }        public void setHeight(Integer height)    {        this.height = height;    }        // 跳转到添加广告页面    @Action(value = "toImageUpload", results = { @Result(name = "success", location = "/WEB-INF/banner/ImgFileUpload.jsp") })    public String toImageUpload()    {        return SUCCESS;    }        @Action(value = "imageUpload", results = { @Result(name = "success", type = "json") }, params = { "contentType", "text/html" })    public String imageUpload()    {        String path = ServletActionContext.getServletContext().getRealPath(PropertiesLoader.getUserFilesPath() + PropertiesLoader.getImageResourceTypePath()) + "/";        FileUtil.newFolder(path);        try        {            File f = this.getFile();            if (this.getFileFileName().endsWith(".exe"))            {                message = "对不起,你上传的文件格式不允许!!!";                return INPUT;            }            FileInputStream inputStream = new FileInputStream(f);            FileOutputStream outputStream = new FileOutputStream(path + "/" + this.getFileFileName());            byte[] buf = new byte[1024];            int length = 0;            while ((length = inputStream.read(buf)) != -1)            {                outputStream.write(buf, 0, length);            }            inputStream.close();            outputStream.flush();            message = fileFileName;            File imageFile = new File(path + "/" + fileFileName);            Image image = ImageIO.read(imageFile);            width = image.getWidth(null);            height = image.getHeight(null);        }        catch (Exception e)        {            e.printStackTrace();            message = "对不起,文件上传失败了!!!!";        }        return SUCCESS;    }}