If there are special characters, InputStream's read () return value will be greater than 255. (the javadoc say the range should be 0-255)

The InputStream knows nothing about encodings. It processes bytes. To make it work, you need to match the database encoding with the JDBC driver and the JVM one as well. If all parties use the same encoding, things should be fine.

In this context, if you think there is a problem with the PostgreSQL Clob handling, try to replicate it with some test from the Hibernate codebase. If it is the ClobProxy, then we need to see why it's failing in the first place.