通过postgres中的bytea数据类型通过SetIcon更新JLabel [英] Updating JLabel via SetIcon from bytea data type in postgres

问题描述

我正在从Wolfram | Alpha检索gif图像。为了最大限度地减少查询，我想存储这些图像，并且只在数据更改时查询W | A，所以我将图像存储为我的 bytea 数据类型postgres db。 保存部分似乎正在起作用，因为有数据。 的System.out.println（rs.getString（ fnPlotImg））产生这样的： \x4275666665726564496d6167654035356437373834323a2074797065203d203120446972656374436f6c6f724d6f64656c3a20726d61736b3d66663030303020676d61736b3d6666303020626d61736b3d666620616d61736b3d3020496e7465676572496e7465726c65617665645261737465723a207769647468203d2032303020686569676874203d20313335202342616e6473203d203320784f6666203d203020794f6666203d203020646174614f66667365745b305d2030

I am retrieving gif images from Wolfram|Alpha. In an effort to minimize queries I want to store those images and only query W|A when the data is changed, so I am storing the images as a bytea data type in my postgres db. The "save" portion seems to be working because there is data. System.out.println(rs.getString("fnPlotImg")) yields this: \x4275666665726564496d6167654035356437373834323a2074797065203d203120446972656374436f6c6f724d6f64656c3a20726d61736b3d66663030303020676d61736b3d6666303020626d61736b3d666620616d61736b3d3020496e7465676572496e7465726c65617665645261737465723a207769647468203d2032303020686569676874203d20313335202342616e6473203d203320784f6666203d203020794f6666203d203020646174614f66667365745b305d2030

我已经能够使用这段代码成功更新W | A中的图像：

I have been able to successfully update the image from W|A using this bit of code:

String path = ((WAImage) element).getURL();
URL url = new URL(path);
BufferedImage image = ImageIO.read(url);
picLabel.setIcon(new ImageIcon(image));

我想用数据库中的图像更新我的应用程序并尝试此代码：

I would like to update my application with the image from the database and have attempted this code:

byte[] ba = rs.getBytes("fnPlotImg");
try{
    picLabel.setIcon(new ImageIcon(ba));
} catch (NullPointerException e) {
    e.printStackTrace();
}

我的理由是bytea是一个字节数组，getBytes（）应该是检索一个字节数组，ImageIcon（）应该处理一个字节数组。但是，如果我没有构建一个空指针异常，它就会出错。我认为这是因为我没有正确地将图像保存到DB或者我没有正确地检索它。

My rationale is that bytea is a byte array, getBytes() is supposed to retrieve a byte array, and ImageIcon() is supposed to handle a byte array.However, if I don't build in a null pointer exception it errors out. I presume this is because I am not saving the image to DB correctly or I am not retrieving it correctly.

欢迎所有的想法，我感到疲惫所以我'我会在早上用新鲜的眼睛检查。

All thoughts are welcome, I'm getting fatigued so I'll check in the morning with fresh eyes.

推荐答案

我没有安装PostgreSQL，但我认为你应该写/读图像格式而不是 BufferedImage 数据。

I don't have a installation of PostgreSQL available, but I think you should be writing/reading the image format and not the BufferedImage data.

例如，写作可能看起来像。 ..

For example, writing might look something like...

Connection con = ...;
BufferedImage img = ...;
try (PreparedStatement stmt = con.prepareStatement("insert into tableofimages (image) values (?)")) {
    try (ByteArrayOutputStream baos = new ByteArrayOutputStream()) {
        ImageIO.write(img, "png", baos);
        try (ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray())) {
            stmt.setBinaryStream(1, bais);
            int rows = stmt.executeUpdate();
            System.out.println(rows + " rows updated");
        }
    }
} catch (SQLException | IOException exp) {
    exp.printStackTrace();
}

阅读可能看起来像......

And reading might look something like...

Connection con = ...;
try (PreparedStatement stmt = con.prepareStatement("select image from tableofimages")) {
    try (ResultSet rs = stmt.executeQuery()) {
        while (rs.next()) {
            try (InputStream is = rs.getBinaryStream(1)) {
                BufferedImage img = ImageIO.read(is);
            }
        }
    }
} catch (SQLException | IOException exp) {
    exp.printStackTrace();
}

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