jsf - 在 JSF 中创建并显示缩略图 (byte[])

Question

我正在将图像上传到服务器，当图像上传时，它应该显示上传图像的缩略图。缩略图未保存在硬盘上我使用InputStream 和OutputStream。对于上传，我是 ustig tomahawk。

我的index.jsp:

<h:form id="uploadForm" enctype="multipart/form-data">
  <t:inputFileUpload id="fileupload" 
    accept="image/*" 
    storage="file"
    value="#{fileUpload.uploadedFile}" 
    styleClass="fileUploadInput"
    required="true" 
    validator="epacient.FileUploadValidator"
    requiredMessage="Obvezna izbira datoteke." 
  />
  <br />
  <h:message for="fileupload" infoStyle="color: green;"
    errorStyle="color: red;" />
  <br />
  <h:commandButton value="Upload" id="fileUploadButton"
    action="#{fileUpload.upload}" />
  <h:message for="uploadForm" style="color: red;" />
  <h:graphicImage value="#{fileUpload.thumb}"
    rendered="#{fileUpload.uploaded}" />

</h:form>

fileUpload.upload调用函数String preview()

private  String thumb ;
public String preview() throws IOException{
  HttpServletResponse response = (HttpServletResponse)FacesContext
    .getCurrentInstance().getExternalContext().getResponse();
  try {
    FacesContext context = FacesContext.getCurrentInstance();
    Map requestMap = context.getExternalContext().getApplicationMap();
    byte[] bytes = (byte[])(requestMap.get("fileupload_bytes")); 
    // returns byte[]
    byte[] testByte = createThumbnail(bytes, 200);
    // here thumbnail is created
  } catch (Exception ex) {
    ex.printStackTrace();
  }
}

创建缩略图:

public static byte[] createThumbnail( byte[] orig, int maxDim) {
  try {
    ImageIcon imageIcon = new ImageIcon(orig);
    Image inImage = imageIcon.getImage();
    double scale = (double) maxDim / (double) inImage.getWidth(null);

    int scaledW = (int) (scale * inImage.getWidth(null));
    int scaledH = (int) (scale * inImage.getHeight(null));

    BufferedImage outImage = new BufferedImage(scaledW, scaledH, BufferedImage.TYPE_INT_RGB);
    AffineTransform tx = new AffineTransform();

    if (scale < 1.0d) {
      tx.scale(scale, scale);
    }

    Graphics2D g2d = outImage.createGraphics();
    g2d.drawImage(inImage, tx, null);
    g2d.dispose();  

    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ImageIO.write(outImage, "JPG", baos);
    byte[] bytesOut = baos.toByteArray();

    return bytesOut;
  } catch (IOException e) {
    System.out.println("Erro: " + e.getMessage());
    e.printStackTrace();
  }
  return null;
}

现在我有了缩略图，但它在 byte[] 中谁能告诉我如何用 <h:graphicImage> 显示我的拇指标签？或者任何其他方式。

谢谢!

Answer 1

每个图像都被视为单独的请求。您不能在单个请求/响应周期中同时处理(JSF 的)HTML 响应和图像。您需要将图像/拇指存储在数据存储中的某个位置，该数据存储的生命周期比请求长，例如服务器的本地磁盘文件系统(临时文件夹？webcontent 文件夹？)，或者数据库(临时表？)，或者在 session 中。

首先，替换

<h:graphicImage value="#{fileUpload.thumb}" ...

由

<h:graphicImage value="thumbs/#{fileUpload.thumbId}" ...

使其生成为

<img src="thumbs/123" ...

(src 应指向有效 URL)

然后，创建一个映射到 /thumbs/* 的 url-pattern 的 HttpServlet 并实现 doGet() 大致如下:

Long thumbId = Long.valueOf(request.getPathInfo().substring(1)); // 123
byte[] thumb = getItFromDiskOrDatabaseOrSessionByThumbId(thumbId);
String filename = getOriginalFilenameOfUploadedImageOrInventOne();

response.setContentType(getServletContext().getMimeType(filename));
response.setContentLength(thumb.length);
response.setHeader("Content-Disposition", "inline; filename=\"" + filename + "\"");

BufferedInputStream input = null;
BufferedOutputStream output = null;

try {
    input = new BufferedInputStream(new ByteArrayInputStream(thumb));
    output = new BufferedOutputStream(response.getOutputStream());
    byte[] buffer = new byte[8192];
    int length;
    while ((length = input.read(buffer)) > 0) {
        output.write(buffer, 0, length);
    }
} finally {
    if (output != null) try { output.close(); } catch (IOException logOrIgnore) {}
    if (input != null) try { input.close(); } catch (IOException logOrIgnore) {}
}

就是这样。更多servlet提示可以在this article中找到.