Java errors
High-intent troubleshooting for parsing and validation errors in Java. Use the exact error message and fix the first real issue.
TL;DR: Validate strictly, fix the first error, then validate again before converting.
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Top tools (local-only)
- JSON Validator
- JSON Repair
- YAML Validator
- CSV Validator
- XML to JSON
- Base64 Encode/Decode
- URL Encode/Decode
- JWT Decoder
JSON parse / deserialize errors
Most issues are not “bad JSON” but wrong content (HTML), truncation, extra characters, invalid escapes, or encoding.
- Cannot deserialize instance of `com.fasterxml.jackson.databind.JsonNode` out of START_ARRAY token
- Cannot deserialize instance of `com.fasterxml.jackson.databind.JsonNode` out of START_OBJECT token
- Cannot deserialize instance of `java.lang.Boolean` out of START_ARRAY token
- Cannot deserialize instance of `java.lang.Boolean` out of START_OBJECT token
- Cannot deserialize instance of `java.lang.Integer` out of START_ARRAY token
- Cannot deserialize instance of `java.lang.Integer` out of START_OBJECT token
- Cannot deserialize instance of `java.lang.String` out of START_ARRAY token
- Cannot deserialize instance of `java.lang.String` out of START_OBJECT token
- Cannot deserialize instance of `java.util.ArrayList` out of START_ARRAY token
- Cannot deserialize instance of `java.util.ArrayList` out of START_OBJECT token
- Cannot deserialize instance of `java.util.LinkedHashMap` out of START_ARRAY token
- Cannot deserialize instance of `java.util.LinkedHashMap` out of START_OBJECT token
- Cannot deserialize instance of `java.util.List` out of START_ARRAY token
- Cannot deserialize instance of `java.util.List` out of START_OBJECT token
- Cannot deserialize instance of `java.util.Map` out of START_ARRAY token
- Cannot deserialize instance of `java.util.Map` out of START_OBJECT token
- Cannot deserialize value of type `com.fasterxml.jackson.databind.JsonNode` from Array value (token `JsonToken.START_ARRAY`)
- Cannot deserialize value of type `com.fasterxml.jackson.databind.JsonNode` from Object value (token `JsonToken.START_OBJECT`)
- Cannot deserialize value of type `java.lang.Boolean` from Array value (token `JsonToken.START_ARRAY`)
- Cannot deserialize value of type `java.lang.Boolean` from Object value (token `JsonToken.START_OBJECT`)
- Cannot deserialize value of type `java.lang.Boolean` from String "1"
- Cannot deserialize value of type `java.lang.Boolean` from String "1.23"
- Cannot deserialize value of type `java.lang.Boolean` from String "2026-02-17T16:30:33Z"
- Cannot deserialize value of type `java.lang.Boolean` from String "false"
- Cannot deserialize value of type `java.lang.Boolean` from String "null"
- Cannot deserialize value of type `java.lang.Boolean` from String "true"
- Cannot deserialize value of type `java.lang.Integer` from Array value (token `JsonToken.START_ARRAY`)
- Cannot deserialize value of type `java.lang.Integer` from Object value (token `JsonToken.START_OBJECT`)
- Cannot deserialize value of type `java.lang.Integer` from String "1"
- Cannot deserialize value of type `java.lang.Integer` from String "1.23"
- Cannot deserialize value of type `java.lang.Integer` from String "2026-02-17T16:30:33Z"
- Cannot deserialize value of type `java.lang.Integer` from String "false"
- Cannot deserialize value of type `java.lang.Integer` from String "null"
- Cannot deserialize value of type `java.lang.Integer` from String "true"
- Cannot deserialize value of type `java.lang.String` from Array value (token `JsonToken.START_ARRAY`)
- Cannot deserialize value of type `java.lang.String` from Object value (token `JsonToken.START_OBJECT`)
- Cannot deserialize value of type `java.time.Instant` from String "1"
- Cannot deserialize value of type `java.time.Instant` from String "1.23"
- Cannot deserialize value of type `java.time.Instant` from String "2026-02-17T16:30:33Z"
- Cannot deserialize value of type `java.time.Instant` from String "false"
- Cannot deserialize value of type `java.time.Instant` from String "null"
- Cannot deserialize value of type `java.time.Instant` from String "true"
- Cannot deserialize value of type `java.time.LocalDateTime` from String "1"
- Cannot deserialize value of type `java.time.LocalDateTime` from String "1.23"
- Cannot deserialize value of type `java.time.LocalDateTime` from String "2026-02-17T16:30:33Z"
- Cannot deserialize value of type `java.time.LocalDateTime` from String "false"
- Cannot deserialize value of type `java.time.LocalDateTime` from String "null"
- Cannot deserialize value of type `java.time.LocalDateTime` from String "true"
- Cannot deserialize value of type `java.util.ArrayList` from Array value (token `JsonToken.START_ARRAY`)
- Cannot deserialize value of type `java.util.ArrayList` from Object value (token `JsonToken.START_OBJECT`)
- Cannot deserialize value of type `java.util.LinkedHashMap` from Array value (token `JsonToken.START_ARRAY`)
- Cannot deserialize value of type `java.util.LinkedHashMap` from Object value (token `JsonToken.START_OBJECT`)
- Cannot deserialize value of type `java.util.List` from Array value (token `JsonToken.START_ARRAY`)
- Cannot deserialize value of type `java.util.List` from Object value (token `JsonToken.START_OBJECT`)
- Cannot deserialize value of type `java.util.Map` from Array value (token `JsonToken.START_ARRAY`)
- Cannot deserialize value of type `java.util.Map` from Object value (token `JsonToken.START_OBJECT`)
- Unexpected character ('<' (code 60)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
- Unexpected end-of-input: expected close marker for Array
- Unexpected end-of-input: expected close marker for Object
- Unrecognized token '...': was expecting ('true', 'false' or 'null')
YAML parse errors
YAML is indentation-sensitive. Fix the first reported line/column, then validate again before converting.
- org.yaml.snakeyaml.composer.ComposerException: found duplicate key
- org.yaml.snakeyaml.parser.ParserException: expected <block end>, but found '<block mapping start>'
- org.yaml.snakeyaml.parser.ParserException: while parsing a block mapping
- org.yaml.snakeyaml.scanner.ScannerException: mapping values are not allowed here
- org.yaml.snakeyaml.scanner.ScannerException: while scanning a simple key
XML parsing errors
XML is strict: a single invalid character or unescaped ampersand can break parsing. Fix the first error and re-validate.
- SAXParseException: Content is not allowed in prolog.
- SAXParseException: The element type must be terminated by the matching end-tag.
- SAXParseException: The entity name must immediately follow the '&' in the entity reference.
- SAXParseException: The markup in the document following the root element must be well-formed.
- SAXParseException: The reference to entity must end with the ';' delimiter.
Encoding / token errors (Base64, URL, JWT)
Encoded strings may contain secrets. Decode locally and normalize Base64URL/percent-encoding safely.
- Illegal base64 character
- Illegal base64 character 2d
- Illegal base64 character 5f
- io.jsonwebtoken.ExpiredJwtException: JWT expired
- io.jsonwebtoken.MalformedJwtException: JWT strings must contain exactly 2 period characters.
- io.jsonwebtoken.SignatureException: JWT signature does not match locally computed signature.
- io.jsonwebtoken.UnsupportedJwtException: Unsupported JWT
- URLDecoder: Illegal hex characters in escape (%) pattern
Related hubs
FAQ (quick)
Start here: Errors hub (runs locally, no upload).
Can I fix Java errors without uploading my data? Yes. no-upload.ru tools run locally in your browser (NO UPLOAD). Start with Errors hub and keep samples redacted if you must share them.
What is the fastest safe workflow? Validate first, fix the smallest broken part, then validate again before converting/exporting. This prevents silent downstream issues.
Why does Java errors happen? Most issues come from copy/paste truncation, wrong encoding, non-strict syntax (comments/trailing commas), or a shape mismatch (array vs object).
Which tool should I start with for Java errors? Start with Errors hub. If you still see errors, follow the related playbook/trend report on this page.
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