Java Online Compiler
Write, compile and run Java code in your browser. Ready-to-run templates, common errors, comparison of the best free compilers.
Free Online Java Developer Tools
11 browser-based tools — compile, convert, encode, generate, and debug without leaving your browser.
☕ 11 tools
🔒 100% client-side
⚡ Free, no sign-up
📋 Java snippets included
Compile
Convert
JSON → Java POJO / Record
Paste JSON, get a Java class. POJO, record, or Lombok @Data. Nested objects and arrays handled.
XML → Java POJO
Convert XML to JAXB, Jackson XML, or plain POJO classes. Attributes and nested elements handled automatically.
Java Beautifier & Formatter
Re-indent minified or messy Java code. Configurable indent size, preserves strings and comments.
Encode & Decode
Base64 Encoder / Decoder
Basic, URL-safe and MIME — the three variants of java.util.Base64, exact match. File upload supported.
Java String Escape & Unescape
Turn text into a valid Java string literal (\n, \", \uXXXX). Also unescapes back to plain text.
JWT Decoder
Decode header, payload and signature of any JSON Web Token. Live expiration status, standard claims explained.
Date & Time
Epoch Timestamp Converter
Convert Unix timestamps ↔ human dates in any time zone. Instant, ZonedDateTime, LocalDateTime snippets.
Cron Expression Parser
Unix, Spring or Quartz cron — decoded in plain English with the next 5 executions. @Scheduled snippet included.
DateTimeFormatter Playground
Type any DateTimeFormatter pattern, see the live output. Locales, time zones, edge cases — all client-side.
Generate
Java Online Compiler — run Java without installing anything
The Java Online Compiler embeds OneCompiler's sandbox, which supports Java 17 and 21 with full standard library access. No account, no download, no IDE startup time. Useful for testing a snippet, reproducing a Stack Overflow bug, or running the code examples from any tutorial on this site.
Convert JSON or XML to Java classes instantly
JSON to POJO
When you need to convert JSON to a Java object, the JSON to POJO tool does it in one paste. It infers types, handles nested objects and arrays, and outputs a POJO, a Java record (Java 14+), or Lombok @Data.
XML to POJO
The XML to Java POJO converter generates JAXB-annotated, Jackson XML, or plain classes. Useful for SOAP services and legacy XML feeds with no existing client library.
Java Beautifier
Need to format Java code quickly without opening IntelliJ IDEA? The Beautifier re-indents your code and normalises brace placement in under a second.
Encoding, decoding and string escaping
Java's java.util.Base64 has three non-interchangeable variants. The Base64 tool matches each one exactly — Basic, URL-safe (-_ instead of +/), and MIME (76-char line wraps).
Escape sequences in Java (\n, \t, \", \\, \uXXXX) are easy to get wrong by hand. The String Escape tool converts any raw text to a valid Java literal and back.
The JWT Decoder splits any JSON Web Token into its three parts, decodes them, and shows every claim — including live exp / nbf status. Nothing is sent to a server. The page also shows how to generate a JWT token in Java with JJWT and Nimbus JOSE + JWT.
Date, time and scheduling
The Epoch Timestamp Converter converts Unix timestamps (10-digit seconds, 13-digit milliseconds) to human-readable dates in any time zone, and back — with the matching java.time snippet.
The Cron Expression Parser explains any Unix, Spring @Scheduled, or Quartz expression in plain English and shows the next 5 execution times in your time zone. The DateTimeFormatter Playground lets you live-test any pattern — yyyy vs YYYY, MM vs mm, XXX vs Z — with locale and time-zone switching.
Frequently asked questions
Is there a free Java compiler online?
Yes — the Java Online Compiler uses OneCompiler's sandbox (Java 17 and 21, no account required).
How do I convert JSON to a Java class?
Paste your JSON into the JSON to POJO tool. It infers types, handles nesting, and outputs a POJO, record, or Lombok @Data class.
How do I generate a UUID in Java?
For v4: UUID.randomUUID(). For v7 (time-ordered, better for database indexes): UuidCreator.getTimeOrderedEpoch() from uuid-creator. Or use the UUID Generator directly.
What is an escape sequence in Java?
A backslash followed by a special character: \n (newline), \t (tab), \" (double quote), \\ (backslash), \uXXXX (Unicode). Use the String Escape tool to convert text automatically.
How do I format Java code online?
Paste into the Java Beautifier. It re-indents blocks and normalises braces without touching your strings or comments.
Do these tools send my data to a server?
Only the Compiler (sends code to OneCompiler). Every other tool processes data entirely in your browser — no network request is made.
How do I decode a JWT token?
Paste your token into the JWT Decoder. It shows the decoded header, all payload claims, and whether the token is currently valid or expired.