The JSON data is parsed in {@linkplain JsonReader#setStrictness(Strictness) lenient mode}.\n *\n * @param reader JSON text\n * @return a parse tree of {@link JsonElement}s corresponding to the specified JSON\n * @throws JsonParseException if there is an IOException or if the specified text is not valid\n * JSON\n * @since 2.8.6\n */\n public static JsonElement parseReader(Reader reader) throws JsonIOException, JsonSyntaxException {\n try {\n JsonReader jsonReader = new JsonReader(reader);\n JsonElement element = parseReader(jsonReader);\n if (!element.isJsonNull() && jsonReader.peek() != JsonToken.END_DOCUMENT) {\n throw new JsonSyntaxException(\"Did not consume the entire document.\");\n }\n return element;\n } catch (MalformedJsonException | NumberFormatException e) {\n throw new JsonSyntaxException(e);\n } catch (IOException e) {\n throw new JsonIOException(e);\n }\n }\n\n /**\n * Returns the next value from the JSON stream as a parse tree. Unlike the other {@code parse}\n * methods, no exception is thrown if the JSON data has multiple top-level JSON elements, or if\n * there is trailing data.\n *\n *
If the {@linkplain JsonReader#getStrictness() strictness of the reader} is {@link\n * Strictness#STRICT}, that strictness will be used for parsing. Otherwise the strictness will be\n * temporarily changed to {@link Strictness#LENIENT} and will be restored once this method\n * returns.","sourceCodeStart":94,"sourceCodeEnd":130,"githubUrl":"https://github.com/google/gson/blob/8b8628c65699bc4421696183c62ae0c1b9b281dc/gson/src/main/java/com/google/gson/JsonParser.java#L94-L130","documentation":"JsonParser.parseReader(Reader) parses exactly one top-level JSON value and then verifies the reader is exhausted; if peek() does not return END_DOCUMENT it throws JsonSyntaxException with this message. It guards against concatenated or trailing garbage after the first JSON value, which the lenient parser would otherwise silently accept.","triggerScenarios":"Calling JsonParser.parseReader(new StringReader(\"{}{}\")) or any input with two top-level values, trailing commas/content, or whitespace-separated documents; feeding a stream that contains a value followed by leftover log text.","commonSituations":"Reading NDJSON/log lines as a single document; concatenated API responses in one buffer; copy-paste artifacts (extra brace) in test fixtures; a Reader that was already partially consumed.","solutions":["Use JsonReader.parseReader only on inputs known to contain one top-level value; strip trailing content.","For multiple top-level values, use JsonStreamParser or read repeatedly with JsonReader in a loop.","Validate/trim the string and check for stray characters after the closing token.","Switch to gson.fromJson(json, type) which enforces single-document semantics with clearer errors."],"exampleFix":"// before\nJsonElement e = JsonParser.parseReader(new StringReader(concatenated));\n\n// after (multiple docs)\nJsonStreamParser it = new JsonStreamParser(new StringReader(concatenated));\nwhile (it.hasNext()) {\n JsonElement e = it.next();\n // ...\n}","handlingStrategy":"validation","validationCode":"String trimmed = json.trim();\n// verify only one top-level value before parseReader\ntry (JsonReader r = new JsonReader(new StringReader(trimmed))) {\n r.setStrictness(Strictness.STRICT);\n // single parse + END_DOCUMENT expectation enforced by parseReader\n}\n","typeGuard":"boolean isSingleDocument(String json) {\n JsonReader r = new JsonReader(new StringReader(json));\n try {\n r.skipValue();\n return r.peek() == JsonToken.END_DOCUMENT;\n } catch (Exception ex) { return false; }\n finally { try { r.close(); } catch (IOException ignored) {} }\n}\n","tryCatchPattern":"try {\n JsonElement e = JsonParser.parseReader(reader);\n} catch (JsonSyntaxException ex) {\n if (ex.getMessage().contains(\"Did not consume\")) {\n // switch to JsonStreamParser for multi-doc input\n } else throw ex;\n}\n","preventionTips":["Use JsonStreamParser when input may contain multiple top-level values.","Strip trailing whitespace/comments before parsing.","Validate test fixtures contain exactly one JSON value."],"tags":["parsing","malformed-json","strictness"],"analyzedSha":"8b8628c65699bc4421696183c62ae0c1b9b281dc","analyzedAt":"2026-08-04T19:12:22.202Z","schemaVersion":2}