fix: refresh ImageIO plugins before PDF conversion

server/src/test/java/cn/keking/service/PdfToJpgServiceTests.java

@@ -0,0 +1,51 @@
+package cn.keking.service;
+
+import org.junit.jupiter.api.Test;
+
+import javax.imageio.ImageIO;
+import javax.imageio.spi.IIORegistry;
+import javax.imageio.spi.ImageReaderSpi;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class PdfToJpgServiceTests {
+
+    @Test
+    void shouldRediscoverJbig2ReaderAfterInitialRegistryMiss() {
+        IIORegistry registry = IIORegistry.getDefaultInstance();
+        List<ImageReaderSpi> providers = findJbig2Providers(registry);
+        assertFalse(providers.isEmpty(), "jbig2-imageio must be present on the test class path");
+
+        try {
+            providers.forEach(registry::deregisterServiceProvider);
+            assertFalse(hasJbig2Reader());
+
+            PdfToJpgService.refreshImageIoPlugins();
+
+            assertTrue(hasJbig2Reader());
+        } finally {
+            providers.forEach(registry::registerServiceProvider);
+        }
+    }
+
+    private static List<ImageReaderSpi> findJbig2Providers(IIORegistry registry) {
+        Iterator<ImageReaderSpi> providers = registry.getServiceProviders(
+                ImageReaderSpi.class,
+                provider -> Arrays.stream(((ImageReaderSpi) provider).getFormatNames())
+                        .anyMatch("JBIG2"::equalsIgnoreCase),
+                true
+        );
+        List<ImageReaderSpi> result = new ArrayList<>();
+        providers.forEachRemaining(result::add);
+        return result;
+    }
+
+    private static boolean hasJbig2Reader() {
+        return ImageIO.getImageReadersByFormatName("JBIG2").hasNext();
+    }
+}