alibaba/nacos · error · IllegalStateException

Malformed \uxxxx encoding.

Error message

Malformed \uxxxx encoding.

What it means

Thrown by OriginTrackedPropertiesPropertiesLoader's readUnicode() when a '\u' escape in a .properties file is followed by something other than four hex digits. Java properties require exactly four hex characters after \u.

Solutions

1. Open the offending .properties file and locate the \u escape near the error.
2. Replace the malformed sequence with a valid four-hex-digit escape (e.g. \u00e9 for é), or use the literal UTF-8 character.
3. If '\u' was meant literally (e.g. in documentation text), escape the backslash as '\\u'.
4. Save the file as UTF-8 and use native characters instead of escapes where possible.
5. Run a properties linter/validator to catch stray escapes.

Example fix

# before (broken escape)
app.title=caf\u00eg

# after (valid escape or literal)
app.title=caf\u00e9
# or, in a UTF-8 file:
app.title=café

String v = Files.readString(Path.of(file));
java.util.regex.Matcher m = java.util.regex.Pattern.compile("\\\\u(?!([0-9a-fA-F]{4})).*").matcher(v);
if (m.find()) {
    throw new IllegalStateException("Malformed \\u escape near: " + m.group());
}

try {
    // load properties via OriginTrackedPropertiesLoader
} catch (IllegalStateException e) {
    if (e.getMessage() != null && e.getMessage().contains("Malformed \\uxxxx")) {
        // point user at the offending .properties file and line
    }
    throw e;
}

When it happens

Trigger: A properties file contains a \uXXXX sequence where at least one of the four characters is not 0-9, a-f, or A-F (e.g. '\u00G1', '\u12', '\uXYZW'), or the sequence is truncated (fewer than four chars before EOF).

Common situations: Hand-edited properties with a malformed unicode escape; an editor or encoding-conversion tool corrupted a \u sequence; a file saved as Latin-1 with stray backslash-u sequences; copy/paste of a literal backslash-u meant as text.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Must be a file directory :
• nacos address
• processors multiple must upper than 1
• processors scale must between 0 and 1
• 400

AI-assisted analysis of alibaba/nacos@9b989acdf1 (2026-08-14). Data as JSON: /api/errors/21370a8438da1488. Report an issue: GitHub.

Appendix: source

Thrown at sys/src/main/java/com/alibaba/nacos/sys/env/OriginTrackedPropertiesLoader.java:227

                this.columnNumber = -1;
                read(true);
            } else if (this.character == 'u') {
                readUnicode();
            }
        }
        
        private void readUnicode() throws IOException {
            this.character = 0;
            for (int i = 0; i < 4; i++) {
                int digit = this.reader.read();
                if (digit >= '0' && digit <= '9') {
                    this.character = (this.character << 4) + digit - '0';
                } else if (digit >= 'a' && digit <= 'f') {
                    this.character = (this.character << 4) + digit - 'a' + 10;
                } else if (digit >= 'A' && digit <= 'F') {
                    this.character = (this.character << 4) + digit - 'A' + 10;
                } else {
                    throw new IllegalStateException("Malformed \\uxxxx encoding.");
                }
            }
        }
        
        public boolean isWhiteSpace() {
            return !this.escaped
                && (this.character == ' ' || this.character == '\t' || this.character == '\f');
        }
        
        public boolean isEndOfFile() {
            return this.character == -1;
        }
        
        public boolean isEndOfLine() {
            return this.character == -1 || (!this.escaped && this.character == '\n');
        }
        
        public boolean isListDelimiter() {

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