Error in Logstash Output to PostgreSQL

[ERROR][org.logstash.Logstash]java.lang.IllegalAccessError: tried to access class org.postgresql.Driver$ConnectThread from class org.postgresql.Driver

output{
  US>jdbc{
    driver_jar_path=>"/usr/share/java/postgresql.jar"
    driver_class=>"org.postgresql.Driver"
    connection_string=>"jdbc:postgresql://localhost:5432/testdb"
    statement=>["INSERT INTO test(result1, result2) VALUES(?,?),
      "test1", "test2"
    ]
  }
  stdout {codec=>rubydebug}
}