Avoid charset provider lookups for UTF-8 QR encoding (#2077)

* Avoid charset provider lookups for UTF-8 QR encoding

* Simplify charset lookup handling

1 files changed, 64 insertions, 0 deletions

diff --git a/core/src/test/java/com/google/zxing/common/CharacterSetECITestCase.java b/core/src/test/java/com/google/zxing/common/CharacterSetECITestCase.java
new file mode 100644
index 000000000..2d98dbe79
--- /dev/null
+++ b/core/src/test/java/com/google/zxing/common/CharacterSetECITestCase.java
@@ -0,0 +1,64 @@
+/*
+ * Copyright 2026 ZXing authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.zxing.common;
+
+import com.google.zxing.FormatException;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
+
+/**
+ * Tests {@link CharacterSetECI}.
+ */
+public final class CharacterSetECITestCase extends Assert {
+
+  @Test
+  public void testStandardCharsets() throws FormatException {
+    assertSame(CharacterSetECI.ISO8859_1, CharacterSetECI.getCharacterSetECI(StandardCharsets.ISO_8859_1));
+    assertSame(CharacterSetECI.ISO8859_1, CharacterSetECI.getCharacterSetECIByName("ISO-8859-1"));
+    assertSame(CharacterSetECI.ISO8859_1, CharacterSetECI.getCharacterSetECIByValue(1));
+    assertSame(StandardCharsets.ISO_8859_1, CharacterSetECI.ISO8859_1.getCharset());
+
+    assertSame(CharacterSetECI.UTF8, CharacterSetECI.getCharacterSetECI(StandardCharsets.UTF_8));
+    assertSame(CharacterSetECI.UTF8, CharacterSetECI.getCharacterSetECIByName("UTF-8"));
+    assertSame(CharacterSetECI.UTF8, CharacterSetECI.getCharacterSetECIByValue(26));
+    assertSame(StandardCharsets.UTF_8, CharacterSetECI.UTF8.getCharset());
+
+    assertSame(CharacterSetECI.ASCII, CharacterSetECI.getCharacterSetECI(StandardCharsets.US_ASCII));
+    assertSame(CharacterSetECI.ASCII, CharacterSetECI.getCharacterSetECIByName("US-ASCII"));
+    assertSame(CharacterSetECI.ASCII, CharacterSetECI.getCharacterSetECIByValue(27));
+    assertSame(StandardCharsets.US_ASCII, CharacterSetECI.ASCII.getCharset());
+
+    assertSame(CharacterSetECI.UnicodeBigUnmarked,
+               CharacterSetECI.getCharacterSetECI(StandardCharsets.UTF_16BE));
+    assertSame(CharacterSetECI.UnicodeBigUnmarked, CharacterSetECI.getCharacterSetECIByName("UTF-16BE"));
+    assertSame(CharacterSetECI.UnicodeBigUnmarked, CharacterSetECI.getCharacterSetECIByValue(25));
+    assertSame(StandardCharsets.UTF_16BE, CharacterSetECI.UnicodeBigUnmarked.getCharset());
+  }
+
+  @Test
+  public void testGB18030UsesPrimaryCharset() throws FormatException {
+    if (Charset.isSupported("GB18030")) {
+      assertSame(CharacterSetECI.GB18030, CharacterSetECI.getCharacterSetECIByName("GBK"));
+      assertSame(CharacterSetECI.GB18030, CharacterSetECI.getCharacterSetECIByValue(29));
+      assertEquals(Charset.forName("GB18030"), CharacterSetECI.GB18030.getCharset());
+    }
+  }
+
+}