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4.5. Logging
Hibernate utilizes Simple Logging Facade for Java (SLF4J) in order to log various system events. SLF4J can direct your logging output to several logging frameworks (NOP, Simple, log4j version 1.2, JDK 1.4 logging, JCL or logback) depending on your chosen binding. In order to setup logging you will need
slf4j-api.jar in your classpath together with the jar file for your preferred binding - slf4j-log4j12.jar in the case of Log4J. See the SLF4J documentation for more detail. To use Log4j you will also need to place a log4j.properties file in your classpath. An example properties file is distributed with Hibernate in the src/ directory.
It is recommended that you familiarize yourself with Hibernate's log messages. A lot of work has been put into making the Hibernate log as detailed as possible, without making it unreadable. It is an essential troubleshooting device. The most interesting log categories are the following:
Table 4.9. Hibernate Log Categories
| Category | Function |
|---|---|
org.hibernate.SQL | Log all SQL DML statements as they are executed |
org.hibernate.type | Log all JDBC parameters |
org.hibernate.tool. hbm2ddl | Log all SQL DDL statements as they are executed |
org.hibernate.pretty | Log the state of all entities (max 20 entities) associated with the session at flush time |
org.hibernate.cache | Log all second-level cache activity |
org.hibernate. transaction | Log transaction related activity |
org.hibernate.jdbc | Log all JDBC resource acquisition |
org.hibernate.hql. ast.AST | Log HQL and SQL ASTs during query parsing |
org.hibernate.secure | Log all JAAS authorization requests |
org.hibernate | Log everything. This is a lot of information but it is useful for troubleshooting |
When developing applications with Hibernate, you should almost always work with
debug enabled for the category org.hibernate.SQL, or, alternatively, the property hibernate.show_sql enabled.
