Java – What hibernate error java.lang.ClassNotFoundException: javax.persistence.Persistence means

hibernatejavajpaservlets

I have a simple servlet project with Tomcat 7 and Hibernate 4.3, but I'm getting an error when I try to use Hibernate but don't known what is happening.

Basically, my servlet calls Persistence.createEntityManagerFactory(PERSISTENCE_UNIT), with the factory, it calls factory.createEntityManager() and with the entity manager, it will try to persist an object made with the parameters from Http request.
The server is raising an exception of java.lang.ClassNotFoundException: javax.persistence.Persistence when I call the first method to get the factory from Persistence. Here is the stack:

(unit1 is my package)

java.lang.ClassNotFoundException: javax.persistence.Persistence
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1714)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1559)
    at unit1.dao_hibernate.HibernateDaoAluno.inserir(HibernateDaoAluno.java:16)
    at unit1.servlet.CadastroAluno.doPost(CadastroAluno.java:29)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

Here is HibernateDaoAluno.java:16 line:

EntityManagerFactory factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT);

Consider

private static final String PERSISTENCE_UNIT = "lpoo2_unit1";

And here is my persistence.xml file, in META-INF folder:

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
         http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
        version="2.0">

    <persistence-unit name="lpoo2_unit1">
        <!-- provedor/implementacao do JPA -->
        <provider>org.hibernate.ejb.HibernatePersistence</provider>

        <!-- entidade mapaeada -->
        <class>unit1.model.Aluno</class>
        <class>unit1.model.Disciplina</class>
        <class>unit1.model.Professor</class>
        <class>unit1.model.Turma</class>

        <properties>
            <!-- dados da conexao -->
            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost/lpoo2" />
            <property name="javax.persistence.jdbc.user" value="root" />
            <property name="javax.persistence.jdbc.password" value="root" />

            <!-- propriedades do hibernate -->
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect" />
            <property name="hibernate.show_sql" value="false" />
            <property name="hibernate.format_sql" value="true" />

            <!-- atualiza o banco, gera as tableas se for preciso -->
            <property name="hibernate.hbm2ddl.auto" value="update" />

        </properties>
    </persistence-unit>

</persistence>

What am I doing wrong? I need help. Thank you!

Best Answer

Your classpath misses the javax.persistence library. This is part of the Java EE SDK (which you might use when developing your application but it is not part of the Java SE SDK which you surely use to run your Tomcat application server.

Solution:

  • Add the javax.persistence Library to the classpath
  • (Or) Use a Java EE environment to run your tomcat.

Remember you can add libraries to either the classpath when calling java, set it as argument for your tomcat, add it to shared library or add it to your web-application's 'lib' directory.

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