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好吧，我做错了什么？我尝试使用图像预览创建简单的图像上传器。我的数据库中有一个产品，带有一些名称、描述等。还有图像。我的目标是为经理用户创建编辑（然后添加）表单。我创建了一个bean：

package pl.jedenpies.sklep.beans;

import java.awt.image.BufferedImage;
import java.io.IOException;

import javax.faces.bean.ManagedBean;
import javax.faces.bean.ViewScoped;
import javax.imageio.ImageIO;

import org.primefaces.event.FileUploadEvent;

import pl.jedenpies.sklep.dto.Image;
import pl.jedenpies.sklep.utils.ImageUtil;

@ViewScoped @ManagedBean(name = "editProductForm")
public class NewEditProductForm {

    private Image currentThumbnail;
    private Image uploadedImage;
    private Image uploadedThumbnail;

    public void save() {
        System.out.println("Saved");
    }

    public void handleFileUpload(FileUploadEvent event) throws IOException {

        BufferedImage originalImage = ImageIO.read(event.getFile().getInputstream());
        BufferedImage thumbnail = ImageUtil.makeThumbnail(originalImage);
        setUploadedImage(originalImage);
        setUploadedThumbnail(thumbnail);
    }


    public Image getCurrentThumbnail() {
        return currentThumbnail;
    }
    public void setCurrentThumbnail(BufferedImage currentThumbnail) {
        this.currentThumbnail = new Image(currentThumbnail);
    }
    public Image getUploadedImage() {
        return uploadedImage;
    }
    public void setUploadedImage(BufferedImage uploadedImage) {
        this.uploadedImage = new Image(uploadedImage);
    }
    public Image getUploadedThumbnail() {
        return uploadedThumbnail;
    }
    public void setUploadedThumbnail(BufferedImage uploadedThumbnail) {
        this.uploadedThumbnail = new Image(uploadedThumbnail);
    }
}

其中 Image 是一个包装 BufferedImage 并允许创建 StreamedContent 对象的类：

import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;

import javax.imageio.ImageIO;

import org.primefaces.model.DefaultStreamedContent;

public class Image {

    private BufferedImage image;

    public Image() {}

    public Image(BufferedImage image) {
        this.image = image;
    }

    public DefaultStreamedContent stream() throws IOException { 

    if (context.getCurrentPhaseId() == PhaseId.RENDER_RESPONSE) {
        return new DefaultStreamedContent();
    }    

    if (image == null) return null;
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        ImageIO.write(image, "png", os);
        ByteArrayInputStream bais = new ByteArrayInputStream(os.toByteArray());
        return new DefaultStreamedContent(bais, "image/png");
    }
}

我的 xhtml 页面是：

<h:form id="editProductForm">
  <div class="form" style="width: 830px;">

    <p:panel id="imageUploader">
      <c:if test="#{editProductForm.currentThumbnail != null}">
        <p:graphicImage
          styleClass="thumbnail"
          id="currentThumbnail" value="#{editProductForm.currentThumbnail.stream()}" cache="false" />                
      </c:if>
      <c:if test="#{editProductForm.currentThumbnail == null}">
        <p:graphicImage 
          value="/resources/images/logo-plaskie-duze.png"
          styleClass="thumbnail" />
      </c:if>
      <c:if test="#{editProductForm.uploadedThumbnail != null}">
        <p:graphicImage
          styleClass="thumbnail"
          id="uploadedThumbnail" value="#{editProductForm.uploadedThumbnail.stream()}" cache="false" />
      </c:if>
      <c:if test="#{editProductForm.uploadedThumbnail == null}">
        <p:graphicImage
          styleClass="thumbnail empty"
          id="uploadedThumbnail" />
      </c:if>    
      <p:fileUpload 
        style="border: 1px solid green;"
        fileUploadListener="#{editProductForm.handleFileUpload}"        
        auto="true"
        update=":editProductForm:imageUploader"
        mode="advanced"
        dragDropSupport="true"

        sizeLimit="20000000" allowTypes="/(\.|\/)(gif|jpe?g|png)$/">
      </p:fileUpload>
    </p:panel>
  </div>
  </h:form>

当我尝试使用我的新表单时，没有显示新上传的图像。当我将范围更改为@SessionScoped 时，它可以工作。但我对使这个 bean 会话的范围不感兴趣。它甚至可以与视图范围一起使用吗？或者也许我只需要以这种或另一种方式保持图像在会话中？

正如@BalusC 建议的那样，我尝试了“特殊的getter 方法”（我之前也尝试过），但没有结果。当我将范围设置为查看时，方法stream()会被调用一次，PhaseId.RENDER_RESPONSE然后我就会22:10:22,816 SEVERE [org.primefaces.application.resource.StreamedContentHandler] (default task-58) Error in streaming dynamic resource. null进入我的日志。

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