JSON Output
JSON output will appear here
Paste Java HashMap, List, or Map.of() code on the left to generate JSON.
Try Java to JSON with sample input
Java to JSON
Convert HashMap, ArrayList, Map.of() and POJO code to JSON
How to convert Java to JSON
Paste Java HashMap, List, or Map.of() code on the left and copy or download JSON on the right.
1
Paste Java code
Paste your Java data structure into the editor. Works with HashMap/ArrayList statements, Map.of(), List.of(), and double-brace initialization. Click "Sample" for a quick demo.
Multiple patterns - Supports Map.of(), new HashMap(){{ }}, sequential put/add calls, and POJO field assignments.
Instant feedback - Parse errors are shown immediately so you can fix the input.
Java Input Example
HashMap<String, Object> config = new HashMap<>();
config.put("host", "localhost");
config.put("port", 5432);
config.put("ssl", true);2
Review JSON output
The converter parses your Java collections and produces formatted, valid JSON instantly. Nested structures, arrays, and all Java primitive types are handled automatically.
Type-aware conversion - Strings, numbers, booleans, null, and chars are all mapped to their JSON equivalents.
Nested support - Maps inside maps, lists inside maps — variable references are fully resolved.
JSON Output Example
{
"host": "localhost",
"port": 5432,
"ssl": true
}3
Copy or download JSON
Use "Copy" to copy JSON to your clipboard for immediate use in APIs or code, or "Download" to save it as a .json file.
One-click copy - Paste JSON directly into your REST client, config file, or test fixture.
Download .json - Save the output as a timestamped .json file for version control or sharing.
Copy or download JSON
2 Actions
Download
Save as java-to-json-{timestamp}.json
Copy
Copy JSON output to clipboard
Tip: The downloaded file is named java-to-json-{timestamp}.json.
Java to JSON FAQs
Common questions about converting Java collections to JSON
The Java to JSON converter supports the most common Java data-structure patterns: sequential put/add statements (HashMap + ArrayList), factory methods (Map.of(), List.of(), Set.of(), Arrays.asList()), double-brace initialization (new HashMap<>(){{ put(...); }}), and field assignments on POJO-style objects. Nested structures — maps inside maps, lists inside maps — are fully resolved in the output.
Java primitives and their wrappers map directly: String → JSON string, int/long/float/double (including L, f, d suffixes) → JSON number, boolean → JSON true/false, null → JSON null. char literals are converted to single-character strings. Type-cast expressions like (String) value are automatically stripped. Hex literals like 0xFF are converted to their decimal number equivalents.
Yes. The Java to JSON converter fully resolves variable references across statements. Declare an ArrayList<String> roles, fill it with add(), then pass the variable name to a HashMap put() call — the tool nests the array correctly in the JSON output. The same works for HashMap inside HashMap, producing deeply nested JSON objects.
Absolutely. Map.of("key1", val1, "key2", val2, ...) is parsed as a JSON object, and List.of(v1, v2, ...) / Arrays.asList(...) / Set.of(...) are parsed as JSON arrays. Map.ofEntries(Map.entry("k", v), ...) is also supported. These one-liner factory patterns are popular in modern Java (11+) codebases.
JSON is a language-agnostic text format for data exchange. Java's HashMap/LinkedHashMap are runtime objects that can hold typed references, support complex keys, and are not directly serializable to text. JSON objects only support string keys and JSON-typed values. Java to JSON conversion bridges this gap — the tool extracts key-value pairs from Java collection syntax and produces valid, portable JSON that any language or API can consume.
Yes — all Java to JSON parsing happens entirely in your browser using client-side TypeScript. Your Java code is never sent to any server, making this tool safe for proprietary or sensitive codebases. No account is required, there are no usage limits, and it is completely free to use.
JSON EDITOR
Edit, format, and beautify JSON
JSON VALIDATOR
Validate, fix, and inspect JSON
JSON ANALYZER
Compare, measure, and map JSON
EXPORT & SHARE
Convert JSON to other formats
IMPORT TO JSON
Convert other formats to JSON
CODE & FORMATTERS
Generate code and format other languages