從數據庫（SQL）檢索圖像（Long Blob）並將其顯示到JLabel中

Question

public void displayPhoto() {
    con = null;
    rs = null;
    PreparedStatement preparedStatement = null;
    BufferedImage bufImg = null;
    String displaySQL = "select * from images where USERNAME =?";
    try {
        con = getDBConnection();
        preparedStatement = con.prepareStatement(displaySQL);
        preparedStatement.setString(1, currentuser.getText().trim());
        rs = preparedStatement.executeQuery();
        while (rs.next()) {
            InputStream in = rs.getBinaryStream("IMAGES");
            bufImg = ImageIO.read(in);
            displayPhoto.setIcon(new ImageIcon(bufImg));
        }

    } catch (Exception ex) {
        ex.printStackTrace();
   }
}

這是我的代碼，上面寫着NullPointersException.

這是完整的錯誤消息

java.lang.NullPointerException
at javax.swing.ImageIcon.<init>(ImageIcon.java:228)
at MyProfile.displayPhoto(MyProfile.java:398)
at MyProfile.<init>(MyProfile.java:197)
at Login.actionPerformed(Login.java:93)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:702)
at java.awt.EventQueue$4.run(EventQueue.java:700)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

我已經做了一個月了，但是仍然無法從數據庫中檢索圖像，對不起，但是我對ImageIO和Stream的東西一無所知，

• displayPhoto = JLabel

並使用setBounds在Container

• IMAGES =列名，
• images =表名，
• currentuser =帶有用戶文字的標簽

怎么做，為什么我會得到這個錯誤？

Answer 1

您應該檢查您的IMAGES列中沒有該用戶的空值。 但是，最可能的原因是ImageIO無法讀取您存儲的字節。 根據ImageIO.read（）javadoc ：

如果沒有注冊的ImageReader聲稱能夠讀取結果流，則返回null。

最可能的原因是IMAGE類型不是ImageIO可以處理的類型，或者它已損壞並且ImageIO無法讀取它。 從JDK 1.7開始，默認情況下，ImageIO僅處理以下圖像類型：

• JPG
• PNG
• BMP
• WBMP
• GIF

如果您的圖片是其他類型，則需要執行額外的步驟來閱讀它們。