I encountered this using Jackson 2.9.9

The JavaDoc for JsonGenerator.writeString(Reader, len) states that passing a len < 0 will write all contents of the reader. It throws an IndexOutOfBoundsException when the buffer in UTF8JsonGenerator becomes full but is not correctly flushed because the check for a full buffer does not take into account the negative len parameter.

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Index 8000 out of bounds for length 8000 (through reference chain: java.util.ArrayList[2]) at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:394) at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:365) at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:338) at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:123) at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serialize(IndexedListSerializer.java:79) at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serialize(IndexedListSerializer.java:18) at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480) at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319) at com.fasterxml.jackson.databind.ObjectMapper._configAndWriteValue(ObjectMapper.java:3905) at com.fasterxml.jackson.databind.ObjectMapper.writeValue(ObjectMapper.java:3176) at jackson.bug.JacksonBugTest.main(JacksonBugTest.java:36) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:567) at com.intellij.rt.execution.application.AppMainV2.main(AppMainV2.java:131) Suppressed: java.lang.IndexOutOfBoundsException: Range [0, 0 + 8001) out of bounds for length 8000 at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:64) at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckFromIndexSize(Preconditions.java:82) at java.base/jdk.internal.util.Preconditions.checkFromIndexSize(Preconditions.java:343) at java.base/java.util.Objects.checkFromIndexSize(Objects.java:425) at java.base/java.io.ByteArrayOutputStream.write(ByteArrayOutputStream.java:129) at com.fasterxml.jackson.core.json.UTF8JsonGenerator._flushBuffer(UTF8JsonGenerator.java:2085) at com.fasterxml.jackson.core.json.UTF8JsonGenerator.close(UTF8JsonGenerator.java:1127) at com.fasterxml.jackson.databind.util.ClassUtil.closeOnFailAndThrowAsIOE(ClassUtil.java:488) at com.fasterxml.jackson.databind.ObjectMapper._configAndWriteValue(ObjectMapper.java:3907) ... 7 more Caused by: java.lang.ArrayIndexOutOfBoundsException: Index 8000 out of bounds for length 8000 at com.fasterxml.jackson.core.json.UTF8JsonGenerator.writeString(UTF8JsonGenerator.java:503) at jackson.bug.JacksonBugTest$ThingSerializer.serialize(JacksonBugTest.java:45) at jackson.bug.JacksonBugTest$ThingSerializer.serialize(JacksonBugTest.java:40) at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:119) ... 12 more