Java 如何让GWTUpload SingleUploader替换以前选择的映像

我使用GWTUpload SingleUploader来选择和显示照片。如果我选择一张照片，然后改变主意，选择另一张照片，则下一张照片将显示在第一张照片旁边。我怎样才能让它代替以前的照片呢

问候,

格林

package org.AwardTracker.client；
导入com.google.gwt.user.client.Window；
导入com.google.gwt.user.client.ui.Composite；
导入com.google.gwt.user.client.ui.FlowPanel；
导入com.google.gwt.user.client.ui.VerticalPanel；
导入com.google.gwt.user.client.ui.Label；
导入com.google.gwt.user.client.ui.FlexTable；
导入com.google.gwt.user.client.ui.TextBox；
导入com.google.gwt.user.client.ui.Button；
导入com.google.gwt.core.client.gwt；
导入com.google.gwt.event.dom.client.ClickHandler；
导入com.google.gwt.event.dom.client.ClickEvent；
导入com.google.gwt.user.client.rpc.AsyncCallback；
导入com.google.gwt.user.client.rpc.ServiceDefTarget；
导入com.google.gwt.user.client.ui.HorizontalPanel；
导入com.google.gwt.user.client.ui.Image；
导入com.google.gwt.user.client.ui.HasHorizontalAlignment；
导入com.google.gwt.user.client.ui.ListBox；
导入com.google.gwt.i18n.client.DateTimeFormat；
导入gwtupload.client.IFileInput；
导入gwtupload.client.IFileInput.FileInputType；
导入gwtupload.client.IUploadStatus.Status；
导入gwtupload.client.IUploader；
导入gwtupload.client.IUploader.uploadeInfo；
导入gwtupload.client.MultiUploader；
导入gwtupload.client.preloedimage；
导入gwtupload.client.preloadeImage.onLoadPreloadeImage处理程序；
导入gwtupload.client.SingleUploader；
//导入java.awt.image.buffereImage；
导入java.io.File；
导入java.lang.String；
导入java.sql.Date；
导入java.util.List；
导入com.google.gwt.user.client.ui.FileUpload；
导入com.google.gwt.user.datepicker.client.DateBox；
导入com.google.gwt.user.datepicker.client.DateBox.DefaultFormat；
公共类EditYouthMemberView扩展了复合{
专用数据库连接同步rpc；
私有文本框textBoxFirstName；
私有文本框文本框搜索编号；
专用ListBox listBoxSection；
私人ListBox listBoxPack；
私有文本框文本框姓氏；
已存档的专用日期框日期框；
私人邮箱dateBoxPackIn；
专用日期框dateBoxPackOut；
专用日期框dateBoxDOB；
//将显示上载图像缩略图的面板
//最终FlowPanel面板图像=新的FlowPanel（）；
最终水平面板图像=新水平面板（）；
@抑制警告（“弃用”）
public EditYouthMemberView（最终NavHandler NavHandler）{
final java.util.Date todays_Date=new java.util.Date（）；
rpc=（DBConnectionAsync）GWT.create（DBConnection.class）；
ServiceDefTarget=（ServiceDefTarget）rpc；
字符串moduleRelativeURL=GWT.getModuleBaseURL（）+“MySQLConnection”；
target.setServiceEntryPoint（moduleRelativeURL）；
VerticalPanel VerticalPanel=新的VerticalPanel（）；
垂直面板。设置样式名称（“gwt横幅”）；
initWidget（垂直面板）；
HorizontalPanel HorizontalPanel=新的HorizontalPanel（）；
horizontalPanel.setStyleName（“gwt横幅”）；
垂直面板。添加（水平面板）；
水平面板设置宽度（“246px”）；
标签lblHome=新标签（“主页”）；
lblHome.addClickHandler（新的ClickHandler（）{
公共作废一次点击（点击事件）{
}
});
水平面板。添加（lblHome）；
lblHome.setWidth（“46px”）；
Label lblEditAwards=新标签（“编辑奖励”）；
lblEditAwards.addClickHandler（新的ClickHandler（）{
公共作废一次点击（点击事件）{
}
});
水平面板。添加（lblEditAwards）；
lblEditAwards.setWidth（“85px”）；
标签lblListAll=新标签（“列出所有幼童军”）；
lblListAll.addClickHandler（新的ClickHandler（）{
公共作废一次点击（点击事件）{
}
});
水平面板。添加（lblListAll）；
lblListAll.setWidth（“130px”）；
Label lblAccountUpdate=新标签（“账户更新”）；
lblAccountUpdate.addClickHandler（新的ClickHandler（）{
公共作废一次点击（点击事件）{
}
});
添加（lblAccountUpdate）；
lblAccountUpdate.setWidth（“104px”）；
FlexTable FlexTable_1=新的FlexTable（）；
垂直面板。添加（flexTable_1）；
Label lblSurname=新标签（“姓氏”）；
lblSurname.setWordWrap（false）；
lblSurname.setHorizontalAlignment（HasHorizontalAlignment.ALIGN_LEFT）；
lblSurname.setStyleName（“gwt标签登录”）；
flexTable_1.setWidget（0,2，lblSurname）；
标签lblFirstName=新标签（“名字”）；
lblFirstName.setWordWrap（false）；
lblFirstName.setHorizontalAlignment（HasHorizontalAlignment.ALIGN_LEFT）；
lblFirstName.setStyleName（“gwt标签登录”）；
flexTable_1.setWidget（0,3，lblFirstName）；
TextBox姓氏=新的TextBox（）；
flexTable_1.setWidget（1，1，TextBoxName）；
textBoxFirstName=newtextbox（）；
flexTable_1.setWidget（1,2，textBoxFirstName）；
标签lbllookforphoto=新标签（“查找照片”）；
lbllookforphoto.setWordWrap（假）；
lbllookforphoto.setHorizontalAlignment（HasHorizontalAlignment.ALIGN_LEFT）；
lbllookforphoto.setStyleName（“gwt标签登录”）；
flexTable_1.setWidget（2,1，lbllookforphoto）；
flexTable_1.getFlexCellFormatter（）.setRowSpan（2,1,3）；
//将图像查看器附加到文档
flexTable_1.setWidget（0,0，panelImages）；
panelImages.setSize（“120”、“120”）；
flexTable_1.getFlexCellFormatter（）.setRowSpan（0,0,4）；
panelImages.clear（）；
//创建一个新的上载面板并将其附加到文档
//final SingleUploader defaultUploader=新的SingleUploader（IFileInput.FileInputType.LABEL，null）；
final SingleUploader defaultUploader=新的SingleUploader（）；
defaultUploader.setAutoSubmit（false）；
defaultUploader.setValidExtensions（“jpg”）；
defaultUploader.setEnabled（true）；
//添加一个将加载imag的完成处理程序
package org.AwardTracker.client;

import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.ui.Composite;
import com.google.gwt.user.client.ui.FlowPanel;
import com.google.gwt.user.client.ui.VerticalPanel;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.FlexTable;
import com.google.gwt.user.client.ui.TextBox;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.core.client.GWT;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.google.gwt.user.client.rpc.ServiceDefTarget;
import com.google.gwt.user.client.ui.HorizontalPanel;
import com.google.gwt.user.client.ui.Image;
import com.google.gwt.user.client.ui.HasHorizontalAlignment;
import com.google.gwt.user.client.ui.ListBox;
import com.google.gwt.i18n.client.DateTimeFormat;

import gwtupload.client.IFileInput;
import gwtupload.client.IFileInput.FileInputType;
import gwtupload.client.IUploadStatus.Status;
import gwtupload.client.IUploader;
import gwtupload.client.IUploader.UploadedInfo;
import gwtupload.client.MultiUploader;
import gwtupload.client.PreloadedImage;
import gwtupload.client.PreloadedImage.OnLoadPreloadedImageHandler;
import gwtupload.client.SingleUploader;

//import java.awt.image.BufferedImage;
import java.io.File;
import java.lang.String;
import java.sql.Date;
import java.util.List;

import com.google.gwt.user.client.ui.FileUpload;
import com.google.gwt.user.datepicker.client.DateBox;
import com.google.gwt.user.datepicker.client.DateBox.DefaultFormat;

public class EditYouthMemberView extends Composite {

private DBConnectionAsync rpc;
private TextBox textBoxFirstName;
private TextBox textBoxScoutNumber;
private ListBox listBoxSection;
private ListBox listBoxPack;
private TextBox textBoxSurname;
private DateBox dateBoxArchived;
private DateBox dateBoxPackIn;
private DateBox dateBoxPackOut;
private DateBox dateBoxDOB;
// A panel where the thumbnails of upload images will be shown
//final FlowPanel panelImages = new FlowPanel();
final HorizontalPanel panelImages = new HorizontalPanel();


@SuppressWarnings("deprecation")
public EditYouthMemberView(final NavHandler navHandler) {       

    final java.util.Date todays_date = new java.util.Date();

    rpc = (DBConnectionAsync) GWT.create(DBConnection.class);
    ServiceDefTarget target = (ServiceDefTarget) rpc;
    String moduleRelativeURL = GWT.getModuleBaseURL() + "MySQLConnection";
    target.setServiceEntryPoint(moduleRelativeURL);

    VerticalPanel verticalPanel = new VerticalPanel();
    verticalPanel.setStyleName("gwt-Banner");
    initWidget(verticalPanel);

    HorizontalPanel horizontalPanel = new HorizontalPanel();
    horizontalPanel.setStyleName("gwt-Banner");
    verticalPanel.add(horizontalPanel);
    horizontalPanel.setWidth("246px");

    Label lblHome = new Label("Home");
    lblHome.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent event) {
        }
    });
    horizontalPanel.add(lblHome);
    lblHome.setWidth("46px");

    Label lblEditAwards = new Label("Edit Awards");
    lblEditAwards.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent event) {
        }
    });
    horizontalPanel.add(lblEditAwards);
    lblEditAwards.setWidth("85px");

    Label lblListAll = new Label("List all Cub Scouts");
    lblListAll.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent event) {
        }
    });
    horizontalPanel.add(lblListAll);
    lblListAll.setWidth("130px");

    Label lblAccountUpdate = new Label("Account Update");
    lblAccountUpdate.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent event) {
        }
    });
    horizontalPanel.add(lblAccountUpdate);
    lblAccountUpdate.setWidth("104px");

    FlexTable flexTable_1 = new FlexTable();
    verticalPanel.add(flexTable_1);

    Label lblSurname = new Label("Surname");
    lblSurname.setWordWrap(false);
    lblSurname.setHorizontalAlignment(HasHorizontalAlignment.ALIGN_LEFT);
    lblSurname.setStyleName("gwt-Label-Login");
    flexTable_1.setWidget(0, 2, lblSurname);

    Label lblFirstName = new Label("First Name");
    lblFirstName.setWordWrap(false);
    lblFirstName.setHorizontalAlignment(HasHorizontalAlignment.ALIGN_LEFT);
    lblFirstName.setStyleName("gwt-Label-Login");
    flexTable_1.setWidget(0, 3, lblFirstName);

    textBoxSurname = new TextBox();
    flexTable_1.setWidget(1, 1, textBoxSurname);

    textBoxFirstName = new TextBox();
    flexTable_1.setWidget(1, 2, textBoxFirstName);      

    Label lblLookForPhotograph = new Label("Look for photograph:");
    lblLookForPhotograph.setWordWrap(false);
    lblLookForPhotograph.setHorizontalAlignment(HasHorizontalAlignment.ALIGN_LEFT);
    lblLookForPhotograph.setStyleName("gwt-Label-Login");
    flexTable_1.setWidget(2, 1, lblLookForPhotograph);
    flexTable_1.getFlexCellFormatter().setRowSpan(2, 1, 3);

    // Attach the image viewer to the document
    flexTable_1.setWidget(0, 0, panelImages);
    panelImages.setSize("120", "120");
    flexTable_1.getFlexCellFormatter().setRowSpan(0, 0, 4);
    panelImages.clear();

    // Create a new uploader panel and attach it to a document
    //final SingleUploader defaultUploader = new SingleUploader(IFileInput.FileInputType.LABEL, null);
    final SingleUploader defaultUploader = new SingleUploader();
    defaultUploader.setAutoSubmit(false);
    defaultUploader.setValidExtensions("jpg");
    defaultUploader.setEnabled(true);

    // Add a finish handler which will load the image once the upload finishes
    defaultUploader.addOnFinishUploadHandler(onFinishUploaderHandler);
    defaultUploader.getFileInput().getWidget().setStyleName("customButton"); 
    defaultUploader.getFileInput().getWidget().setSize("159px", "27px");
    defaultUploader.avoidRepeatFiles(true);
    //defaultUploader.setServletPath(defaultUploader.getServletPath() + "?caseId=" + caseObj.getId().toString());

    flexTable_1.setWidget(3, 1, defaultUploader);
    flexTable_1.getFlexCellFormatter().setRowSpan(3, 1, 3);

    FlexTable flexTable = new FlexTable();
    verticalPanel.add(flexTable);

    Label lblDOB = new Label("Date of Birth:");
    lblDOB.setWordWrap(false);
    lblDOB.setStyleName("gwt-Label-Login");
    flexTable.setWidget(0, 0, lblDOB);
    lblDOB.setDirectionEstimator(false);
    lblDOB.setHorizontalAlignment(HasHorizontalAlignment.ALIGN_RIGHT);
    lblDOB.setSize("110px", "16px");

    dateBoxDOB = new DateBox();
    dateBoxDOB.setFormat(new DefaultFormat(DateTimeFormat.getFormat("dd-MM-yyyy")));
    flexTable.setWidget(0, 1, dateBoxDOB);
    dateBoxDOB.getDatePicker();

    Label lblSection = new Label("Section:");
    lblSection.setHorizontalAlignment(HasHorizontalAlignment.ALIGN_RIGHT);
    lblSection.setStyleName("gwt-Label-Login");
    flexTable.setWidget(0, 2, lblSection);

    listBoxSection = new ListBox();
    listBoxSection.addItem("Cubs");
    flexTable.setWidget(0, 3, listBoxSection);
    listBoxSection.setVisibleItemCount(1);

    Label lblScoutNumber = new Label("Scout Number:");
    lblScoutNumber.setHorizontalAlignment(HasHorizontalAlignment.ALIGN_RIGHT);
    lblScoutNumber.setStyleName("gwt-Label-Login");
    flexTable.setWidget(1, 0, lblScoutNumber);
    lblScoutNumber.setDirectionEstimator(false);
    lblScoutNumber.setSize("110px", "16px");

    textBoxScoutNumber = new TextBox();
    flexTable.setWidget(1, 1, textBoxScoutNumber);

    Label lblPack = new Label("Pack:");
    lblPack.setHorizontalAlignment(HasHorizontalAlignment.ALIGN_RIGHT);
    lblPack.setStyleName("gwt-Label-Login");
    flexTable.setWidget(1, 2, lblPack);

    listBoxPack = new ListBox();
    listBoxPack.addItem("Explorer");
    listBoxPack.addItem("Pioneer");
    flexTable.setWidget(1, 3, listBoxPack);
    listBoxPack.setVisibleItemCount(1);

    Label lblDateArchived = new Label("Date Archived:");
    lblDateArchived.setHorizontalAlignment(HasHorizontalAlignment.ALIGN_RIGHT);
    lblDateArchived.setStyleName("gwt-Label-Login");
    flexTable.setWidget(2, 0, lblDateArchived);
    lblDateArchived.setSize("110px", "16px");

    dateBoxArchived = new DateBox();
    dateBoxArchived.setFormat(new DefaultFormat(DateTimeFormat.getFormat("dd-MM-yyyy")));
    flexTable.setWidget(2, 1, dateBoxArchived);
    dateBoxArchived.getDatePicker();

    Label lblIn_1 = new Label("In:");
    lblIn_1.setHorizontalAlignment(HasHorizontalAlignment.ALIGN_RIGHT);
    lblIn_1.setStyleName("gwt-Label-Login");
    flexTable.setWidget(2, 2, lblIn_1);

    dateBoxPackIn = new DateBox();
    dateBoxPackIn.setFormat(new DefaultFormat(DateTimeFormat.getFullDateFormat()));
    flexTable.setWidget(2, 3, dateBoxPackIn);
    dateBoxPackIn.getDatePicker();

    Label lblNewLabel_3 = new Label("Out:");
    lblNewLabel_3.setStyleName("gwt-Label-Login");
    flexTable.setWidget(2, 4, lblNewLabel_3);

    dateBoxPackOut = new DateBox();
    dateBoxPackOut.setFormat(new DefaultFormat(DateTimeFormat.getFormat("dd-MM-yyyy")));
    dateBoxPackOut.getDatePicker();

    flexTable.setWidget(2, 5, dateBoxPackOut);

    Button btnAdd = new Button("Add");
    btnAdd.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent event) {
            Integer tracker = 0;
            if (textBoxSurname.getText().length() == 0) {
                tracker = tracker + 1; 
            }
            if (textBoxFirstName.getText().length() == 0) {
                tracker = tracker + 2; 
            }
            //TO DO
            // How do I check that a picture has been selected?
            // if (panelImages.getFilename().length() == 0) {
            //  tracker = tracker + 4; 
            // }
            if (dateBoxDOB.toString().length() == 0) {
                tracker = tracker + 8; 
            }
            if (dateBoxPackIn.toString().length() == 0) {
                tracker = tracker + 16; 
            }

            if (tracker == 1) {
                Window.alert("Please enter a Surname.");
            }
            if (tracker == 2) {
                Window.alert("Please enter a First Name.");
            }
            if (tracker == 3) {
                Window.alert("Please enter Surname and First Name");
            }
            if (tracker == 4) {
                Window.alert("Please select a photograph.");
            }
            if (tracker == 5) {
                Window.alert("Please enter a Surname and select a photograph.");
            }
            if (tracker == 6) {
                Window.alert("Please enter a FirstName and select a photograph.");
            }
            if (tracker == 7) {
                Window.alert("Please enter Surname, First Name and select a photograph");
            }
            if (tracker == 8) {
                Window.alert("Please enter a DOB");
            }
            if (tracker == 9) {
                Window.alert("Please enter a Surname and DOB");
            }
            if (tracker == 10) {
                Window.alert("Please enter a First Name and DOB");
            }
            if (tracker == 11) {
                Window.alert("Please enter a Surname, First Name and DOB");
            }
            if (tracker == 12) {
                Window.alert("Please select a photograph and enter a BOB");
            }
            if (tracker == 13) {
                Window.alert("Please enter a Surname, select a photograph and enter a DOB");
            }
            if (tracker == 14) {
                Window.alert("Please enter a FirstName, select a photograph and enter a DOB");
            }
            if (tracker == 15) {
                Window.alert("Please enter Surname, First Name, select a photograph and enter a DOB");
            }
            if (tracker == 16) {
                Window.alert("Please enter date joined Pack");
            }

            if (tracker == 17) {
                Window.alert("Please enter a Surname and date joined Pack.");
            }
            if (tracker == 18) {
                Window.alert("Please enter a First Name and date joined Pack.");
            }
            if (tracker == 19) {
                Window.alert("Please enter Surname, First Name and date joined Pack");
            }
            if (tracker == 20) {
                Window.alert("Please select a photograph and enter date joined Pack.");
            }
            if (tracker == 21) {
                Window.alert("Please enter a Surname, select a photograph and enter date joined Pack.");
            }
            if (tracker == 22) {
                Window.alert("Please enter a First Name, select a photograph and enter date joined Pack.");
            }
            if (tracker == 23) {
                Window.alert("Please enter Surname, First Name, select a photograph and enter date joined Pack");
            }
            if (tracker == 24) {
                Window.alert("Please enter a DOB and date joined Pack");
            }
            if (tracker == 25) {
                Window.alert("Please enter a Surname, DOB and date joined Pack");
            }
            if (tracker == 26) {
                Window.alert("Please enter a First Name, DOB and date joined Pack");
            }
            if (tracker == 27) {
                Window.alert("Please enter a Surname, First Name, DOB and date joined Pack");
            }
            if (tracker == 28) {
                Window.alert("Please select a photograph, enter a BOB and date joined Pack");
            }
            if (tracker == 29) {
                Window.alert("Please enter a Surname, select a photograph, enter a DOB and date joined Pack");
            }
            if (tracker == 30) {
                Window.alert("Please enter a FirstName, select a photograph, enter a DOB and date joined Pack");
            }
            if (tracker == 31) {
                Window.alert("Please enter Surname, First Name, select a photograph, enter a DOB and date joined Pack");
            }

            //if (tracker == 0) {
            //  AsyncCallback<YthMmbrSectDtls> callback = new CreationHandler<YthMmbrSectDtls>(null);
            //  rpc.createYouthMember(null, textBoxSurname.getText(), textBoxFirstName.getText(), dateBoxDOB.getValue(), 
            //          fileUpload.getFilename(), dateBoxArchived.getValue(), null, listBoxSection.getItemText(listBoxSection.getSelectedIndex()),
            //          listBoxPack.getItemText(listBoxPack.getSelectedIndex()), dateBoxPackIn.getValue(), 
            //          dateBoxPackOut.getValue(), callback);
            //}

        }

    });
    flexTable.setWidget(3, 0, btnAdd);

    Button btnUpdate = new Button("Update");
    btnUpdate.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent event) {
        }
    });
    btnUpdate.setText("Update");
    flexTable.setWidget(3, 1, btnUpdate);

    Button btnCancel = new Button("Cancel");
    btnCancel.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent event) {
        }
    });
    btnCancel.setText("Cancel");
    flexTable.setWidget(3, 2, btnCancel);

    Button btnClearPage = new Button("Clear Page");
    btnClearPage.setText("Clear Page");
    btnClearPage.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent event) {
            textBoxSurname.setText("");
            textBoxFirstName.setText("");
            dateBoxDOB.setValue(null);
            dateBoxPackIn.setValue(todays_date);
            dateBoxPackOut.setValue(null);
            textBoxScoutNumber.setText("");
            dateBoxArchived.setValue(null);
        }
    });
    flexTable.setWidget(3, 3, btnClearPage);
    setStyleName("body");
}

// Load the image in the document and in the case of success attach it to the viewer
private IUploader.OnFinishUploaderHandler onFinishUploaderHandler = new IUploader.OnFinishUploaderHandler() {
    public void onFinish(IUploader uploader) {
        if (uploader.getStatus() == Status.SUCCESS) {
            new PreloadedImage(uploader.fileUrl(), showImage);

            //The server sends useful information to the client by default
            UploadedInfo info = uploader.getServerInfo();
            System.out.println("File name " + info.name);
            System.out.println("File content-type " + info.ctype);
            System.out.println("File size " + info.size);

            // You can send any customised message and parse it
            System.out.println("Server message " + info.message);

        }
    }
};

// Attach an image to the pictures viewer
private OnLoadPreloadedImageHandler showImage = new OnLoadPreloadedImageHandler() {
    public void onLoad(PreloadedImage image) {
        image.setWidth("75px");
        panelImages.add(image);
    }
};

/**
 * Decodes the base64 string into byte array to display image
 * Calls Base64Decode.java
 * @param imageDataString - a {@link java.lang.String}
 * @return byte array
 */
public static byte[] decodeImage(String imageDataString) {
    return Base64Decode.decode(imageDataString);
    }

public IUploader.OnFinishUploaderHandler getOnFinishUploaderHandler() {
    return onFinishUploaderHandler;
}

public void setOnFinishUploaderHandler(IUploader.OnFinishUploaderHandler onFinishUploaderHandler) {
    this.onFinishUploaderHandler = onFinishUploaderHandler;
}

}

private Widget lastImage = null;

private OnLoadPreloadedImageHandler showImage = new OnLoadPreloadedImageHandler() {
  public void onLoad(PreloadedImage image) {
    if (lastImage != null) {
      lastImage.removeFromParent()
    }
    lastImage = image;
    image.setWidth("75px");
    panelImages.add(image);
  }
};