JEditorPane with inline image

I'm attempting to display an inline image in a Java JEditorPane. The code below uses HTML content that properly displays the image in Firefox, but not in the JEditorPane. Any ideas why? Thanks.

import javax.swing.*;
import java.awt.*;

public class InlineImage {

    public InlineImage() {
        JFrame frame=new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JEditorPane edit=new JEditorPane();
        frame.getContentPane().add(edit);
        edit.setContentType("text/html");

        String html = "<html><body>Local image<br><img src=\"data:image/png;charset=utf-8;base64,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\"></body></html>";
        edit.setText(html);

        frame.setSize(500,300);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {new InlineImage();}
}

Solution

You need to add a protocol handler for "data:" so an URL/URLConnection can be opened for it. Alternatively you could create some protocol handler "resource:" for class path resources.

You need a package data with a class Handler (fixed name convention!). This will be the factory class for "data:" return an URLConnection. We will create DataConnection for that.

Installing a protocol handler can be done via System.setProperty. Here I provided Handler.install(); to do that in a generic way.

package test1.data;

import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLStreamHandler;

public class Handler extends URLStreamHandler {

    @Override
    protected URLConnection openConnection(URL u) throws IOException {
        return new DataConnection(u);
    }

    public static void install() {
        String pkgName = Handler.class.getPackage().getName();
        String pkg = pkgName.substring(0, pkgName.lastIndexOf('.'));

        String protocolHandlers = System.getProperty("java.protocol.handler.pkgs", "");
        if (!protocolHandlers.contains(pkg)) {
            if (!protocolHandlers.isEmpty()) {
                protocolHandlers += "|";
            }
            protocolHandlers += pkg;
            System.setProperty("java.protocol.handler.pkgs", protocolHandlers);
        }
    }
}

The URLConnection gives an InputStream to the bytes:

package test1.data;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import javax.xml.bind.DatatypeConverter;

public class DataConnection extends URLConnection {

    public DataConnection(URL u) {
        super(u);
    }

    @Override
    public void connect() throws IOException {
        connected = true;
    }

    @Override
    public InputStream getInputStream() throws IOException {
        String data = url.toString();
        data = data.replaceFirst("^.*;base64,", "");
        System.out.println("Data: " + data);
        byte[] bytes = DatatypeConverter.parseBase64Binary(data);
        return new ByteArrayInputStream(bytes);
    }

}

The clever thing here is to use Base64 decoding of DatatypeConverter in standard Java SE.

P.S.

Nowadays one would use Base64.getEncoder().encode(...).