eugenp · KevinGilmore · Nov 17, 2025 · Nov 11, 2025 · Nov 11, 2025 · Nov 11, 2025
diff --git a/...ing-conversions-4/src/main/java/com/baeldung/blobstringconverter/BlobStringConverter.java b/...ing-conversions-4/src/main/java/com/baeldung/blobstringconverter/BlobStringConverter.java
@@ -0,0 +1,57 @@
+package com.baeldung.blobstringconverter;
+
+import java.sql.Blob;
+import java.sql.SQLException;
+import java.nio.charset.StandardCharsets;
+import javax.sql.rowset.serial.SerialBlob;
+
+public class BlobStringConverter {
+
+    /**
+     * Converts a java.sql.Blob object to a String using UTF-8 encoding.
+     * @param blob The Blob object to convert.
+     * @return The String representation of the Blob data.
+     * @throws SQLException If a database access error occurs.
+     */
+    public static String blobToString(Blob blob) throws SQLException {
+        if (blob == null) {
+            return null;
+        }
+
+        long length = blob.length();
+
+        // Check for zero length to avoid SerialException: Invalid arguments.
+        if (length == 0) {
+            return ""; 
+        }
+
+        if (length > Integer.MAX_VALUE) {
+             throw new SQLException("Blob is too large for a single String conversion.");
+        }
+
+        // Get the entire Blob content as a byte array. The position starts at 1.
+        byte[] bytes = blob.getBytes(1, (int) length);
+
+        // Convert the byte array to a String using the UTF-8 charset
+        return new String(bytes, StandardCharsets.UTF_8);
+    }
+
+    /**
+     * Converts a String object to a java.sql.Blob using UTF-8 encoding.
+     * @param text The String to convert.
+     * @return A SerialBlob object containing the String data.
+     * @throws SQLException If a database access error occurs.
+     */
+    public static Blob stringToBlob(String text) throws SQLException {
+        if (text == null) {
+            return null;
+        }
+
+        // Convert the String to a byte array using the UTF-8 charset.
+        // This is safe even for an empty string ("") which results in a zero-length byte array.
+        byte[] bytes = text.getBytes(StandardCharsets.UTF_8);
+
+        // Create a SerialBlob object from the byte array
+        return new SerialBlob(bytes);
+    }  
+}
diff --git a/...ersions-4/src/test/java/com/baeldung/blobstringconverter/BlobStringConverterUnitTest.java b/...ersions-4/src/test/java/com/baeldung/blobstringconverter/BlobStringConverterUnitTest.java
@@ -0,0 +1,68 @@
+package com.baeldung.blobstringconverter;
+
+import org.junit.jupiter.api.Test;
+import java.sql.Blob;
+import java.sql.SQLException;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+public class BlobStringConverterUnitTest {
+
+    // Test a standard ASCII string
+    @Test
+    void givenStandardAsciiString_whenPerformingConversion_thenConversionSuccessful() throws SQLException {
+        String originalString = "Hello, world!";
+
+        // String to Blob
+        Blob blob = BlobStringConverter.stringToBlob(originalString);
+        assertNotNull(blob);
+
+        // Blob to String
+        String convertedString = BlobStringConverter.blobToString(blob);
+
+        // Assert the converted string is equal to the original
+        assertEquals(originalString, convertedString);
+    }
+
+    // Test a string with special characters (important for correct encoding)
+    @Test
+    void givenStringWithSpecialCharacters_whenPerformingConversion_thenConversionSuccessful() throws SQLException {
+        // String with non-ASCII characters (e.g., Japanese, German umlaut)
+        String originalString = "Test: こんにちは, äöü";
+
+        // String to Blob
+        Blob blob = BlobStringConverter.stringToBlob(originalString);
+
+        // Blob to String
+        String convertedString = BlobStringConverter.blobToString(blob);
+
+        assertEquals(originalString, convertedString);
+    }
+
+    // Test an empty string
+    @Test
+    void givenEmptyString_whenPerformingConversion_thenConversionSuccessful() throws SQLException {
+        String originalString = "";
+
+        // String to Blob
+        Blob blob = BlobStringConverter.stringToBlob(originalString);
+
+        // Blob to String
+        String convertedString = BlobStringConverter.blobToString(blob);
+
+        assertEquals(originalString, convertedString);
+    }
+
+    // Test null input for conversion methods
+    @Test
+    void givenNullString_whenPerformingConversion_thenConversionSuccessful() throws SQLException {
+        // Test String to Blob with null
+        assertNull(BlobStringConverter.stringToBlob(null), 
+                   "stringToBlob should return null for null input.");
+
+        // Test Blob to String with null
+        assertNull(BlobStringConverter.blobToString(null), 
+                   "blobToString should return null for null input.");
+    }
+}