Can the Jackson parser be used to parse JSON5?

Question

We'd like to parse JSON5 documents in the JVM, but the JSON5-specific libraries available on GitHub all appear to have very low support. As parsers are often magnets for security vulnerabilities, we'd prefer not to use a parser that isn't already being widely used and scrutinised by the community.

This got us to wondering: Can the optional features of the Jackson JSON parser be used to parse JSON5?

Answer 1

tl;dr

By enabling the following optional Jackson parser features:

• ALLOW_UNQUOTED_FIELD_NAMES
• ALLOW_TRAILING_COMMA
• ALLOW_SINGLE_QUOTES
• ALLOW_BACKSLASH_ESCAPING_ANY_CHARACTER
• ALLOW_NON_NUMERIC_NUMBERS
• ALLOW_JAVA_COMMENTS
• ALLOW_LEADING_DECIMAL_POINT_FOR_NUMBERS

it seems possible to support all of JSON5's headline features except for:

• hexadecimal numbers
• trailing decimal points on numbers
• plus signs before numbers
• extra whitespace characters

Detail

Jackson has a number of optional features which can be enabled on a parser to make it more lenient in the way it parses.

Supported Features

Comparing these parser options to the headline features of JSON5, we find that the following are supported:

Object keys may be an ECMAScript 5.1 IdentifierName.

✅ Supported with the ALLOW_UNQUOTED_FIELD_NAMES feature

Objects may have a single trailing comma.

Arrays may have a single trailing comma.

✅ Both supported with the ALLOW_TRAILING_COMMA feature

Strings may be single quoted.

✅ Supported with the ALLOW_SINGLE_QUOTES feature

Strings may span multiple lines by escaping new line characters.

Strings may include character escapes.

✅ Both of these appear to be supported by Jackson's ALLOW_BACKSLASH_ESCAPING_ANY_CHARACTER feature, though the meaning or purpose of escaping here may differ subtly. DYOR.

Numbers may be IEEE 754 positive infinity, negative infinity, and NaN.

✅ Supported with the ALLOW_NON_NUMERIC_NUMBERS feature

Single and multi-line comments are allowed.

✅ Supported with the ALLOW_JAVA_COMMENTS feature.

Partially Supported Features

The following JSON5 feature is partially supported by Jackson:

Numbers may have a leading or trailing decimal point.

✅ Leading decimal points are supported with the ALLOW_LEADING_DECIMAL_POINT_FOR_NUMBERS feature.

⛔️ Jackson doesn't appear to have support for trailing decimal points.

Unsupported Features

There doesn't currently (mid-2021) appear to be any way to configure Jackson to permit the following JSON5 features:

Numbers may be hexadecimal.

Numbers may have a trailing decimal point.

Numbers may begin with an explicit plus sign.

Additional white space characters are allowed.