Resources containing spaces cannot be read from executable jars after #52246

loader/spring-boot-loader/src/main/java/org/springframework/boot/loader/net/util/UrlEncoder.java

@@ -65,20 +65,28 @@ private static String encode(char[] path, int fromIndex) {
 				result[size++] = ch;
 				continue;
 			}
-			if (ch > 0x07FF) {
-				size = escape(result, 0xE0 | ((ch >> 12) & 0x0F), size);
-				size = escape(result, 0x80 | ((ch >> 6) & 0x3F), size);
-				size = escape(result, 0x80 | ((ch >> 0) & 0x3F), size);
-			}
-			else {
-				size = escape(result, 0xC0 | ((ch >> 6) & 0x1F), size);
-				size = escape(result, 0x80 | ((ch >> 0) & 0x3F), size);
-			}
+			size = encode(ch, result, size);
 		}
 		return new String(result, 0, size);
 	}
 
-	private static int escape(char[] result, int ch, int size) {
+	private static int encode(char ch, char[] result, int size) {
+		if (ch <= 0x007F) {
+			size = encodeByteChar(result, ch, size);
+			return size;
+		}
+		if (ch <= 0x07FF) {
+			size = encodeByteChar(result, 0xC0 | ((ch >> 6) & 0x1F), size);
+			size = encodeByteChar(result, 0x80 | ((ch >> 0) & 0x3F), size);
+			return size;
+		}
+		size = encodeByteChar(result, 0xE0 | ((ch >> 12) & 0x0F), size);
+		size = encodeByteChar(result, 0x80 | ((ch >> 6) & 0x3F), size);
+		size = encodeByteChar(result, 0x80 | ((ch >> 0) & 0x3F), size);
+		return size;
+	}
+
+	private static int encodeByteChar(char[] result, int ch, int size) {
 		result[size++] = '%';
 		result[size++] = HexFormat.of().toHighHexDigit(ch);
 		result[size++] = HexFormat.of().toLowHexDigit(ch);

loader/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/protocol/jar/JarUrlClassLoaderTests.java

@@ -102,6 +102,28 @@ void resolveFromNested() throws Exception {
 		}
 	}
 
+	@Test
+	void resolveFromNestedWhenNameNeedsEncoding() throws Exception {
+		ByteArrayOutputStream nestedJarData = new ByteArrayOutputStream();
+		try (JarOutputStream jarOutputStream = new JarOutputStream(nestedJarData)) {
+			jarOutputStream.putNextEntry(new JarEntry("dir with space/a#b.txt"));
+			jarOutputStream.write(42);
+			jarOutputStream.closeEntry();
+		}
+		File jarFile = new File(this.tempDir, "test.jar");
+		try (JarOutputStream jarOutputStream = new JarOutputStream(new FileOutputStream(jarFile))) {
+			writeStoredEntry(jarOutputStream, "nested.jar", nestedJarData.toByteArray());
+		}
+		URL url = JarUrl.create(jarFile, "nested.jar");
+		try (JarUrlClassLoader loader = new TestJarUrlClassLoader(url)) {
+			URL resource = loader.getResource("dir with space/a#b.txt");
+			assertThat(resource).isNotNull();
+			try (InputStream input = resource.openConnection().getInputStream()) {
+				assertThat(input.read()).isEqualTo(42);
+			}
+		}
+	}
+
 	@Test
 	void resolveFromNestedWhenMissingReturnsNull() throws Exception {
 		File jarFile = new File(this.tempDir, "test.jar");

loader/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/util/UrlEncoderTests.java

@@ -20,11 +20,21 @@ void encodeWhenBasicString() {
 		assertThat(UrlEncoder.encode("a/b/C.class")).isEqualTo("a/b/C.class");
 	}
 
+	@Test
+	void encodeWhenHasSingleByteEncodedCharacters() {
+		assertThat(UrlEncoder.encode("a b/c#d%e?f.txt")).isEqualTo("a%20b/c%23d%25e%3ff.txt");
+	}
+
 	@Test
 	void encodeWhenHasDoubleByteEncodedCharacters() {
 		assertThat(UrlEncoder.encode("\u00e1/b/C.class")).isEqualTo("%c3%a1/b/C.class");
 	}
 
+	@Test
+	void encodeWhenHasTrippleByteEncodedCharacters() {
+		assertThat(UrlEncoder.encode("\u6841/b/C.class")).isEqualTo("%e6%a1%81/b/C.class");
+	}
+
 	@Test
 	void encodeWhenHasMixtureOfEncodedAndUnencodedDoubleByteCharacters() {
 		assertThat(UrlEncoder.encode("\u00e1/b/\u00c7.class")).isEqualTo("%c3%a1/b/%c3%87.class");