Hibernate with Tomcat and gradle

Question

Disclaimer: I'm a Java newbie. I'm trying to setup Hibernate with Tomcat and Gradle. The build runs correctly but it looks like the persistence.xml file is not read

My project structure is as follow:

├── build.gradle
└── src
└── main
    ├── java
    │   └── com
    │       └── test
    │           ├── domain
    │           │   └── Person.java
    │           └── web
    │               └── EventManagerServlet.java
    └── webapp
        ├── META-INF
        │   └── web.xml
        └── WEB-INF
            └── classes
                └── persistence.xml

The content of the build.gradle file:

apply plugin: 'java'
apply plugin: 'idea'
apply plugin: 'tomcat'
apply plugin: 'war'

sourceCompatibility = 1.5
version = '1.0'

repositories {
    mavenCentral()
}

buildscript {
    repositories {
        jcenter()
    }

    dependencies {
        classpath 'org.gradle.api.plugins:gradle-tomcat-plugin:1.2.3'
    }
}

dependencies {
    compile 'javax.servlet:javax.servlet-api:3.0.1'
    compile group: 'org.hibernate', name: 'hibernate-core', version: '4.3.5.Final'
    compile group: 'mysql', name: 'mysql-connector-java', version: '5.1.13'

    def tomcatVersion = '7.0.11'
    tomcat "org.apache.tomcat.embed:tomcat-embed-core:${tomcatVersion}",
            "org.apache.tomcat.embed:tomcat-embed-logging-juli:${tomcatVersion}"
    tomcat("org.apache.tomcat.embed:tomcat-embed-jasper:${tomcatVersion}") {
        exclude group: 'org.eclipse.jdt.core.compiler', module: 'ecj'
    }
}

war {
    webXml = file('src/main/webapp/META-INF/web.xml')
}

The EventManagerServlet class:

package com.test.web;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;

public class EventManagerServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("com");
        EntityManager entityManager = entityManagerFactory.createEntityManager();
    }
}

The persistence.xml file:

<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="com" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <class>com.test.domain.Person</class>
        <properties>
            <property name="hibernate.archive.autodetection" value="class, hbm"/>
            <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
            <property name="hibernate.connection.password"></property>
            <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate</property>
            <property name="hibernate.connection.username">root</property>
            <property name="hibernate.default_schema">hibernate</property>
            <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
            <property name="hibernate.hbm2ddl.auto" value="create"/>

            <property name="hibernate.c3p0.min_size" value="5"/>
            <property name="hibernate.c3p0.max_size" value="20"/>
            <property name="hibernate.c3p0.timeout" value="300"/>
            <property name="hibernate.c3p0.max_statements" value="50"/>
            <property name="hibernate.c3p0.idle_test_period" value="3000"/>
        </properties>
    </persistence-unit>
</persistence>

When I run ./gradlew tomcatRunWar --stacktrace, the server is running on http://localhost:8080/play but when I try to access the page, I get the following exception:

Servlet.service() for servlet [Event Manager] in context with path [/play] threw exception
javax.persistence.PersistenceException: No Persistence provider for EntityManager named com
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:61)
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:39)

The war directory structure:

├── META-INF
│   ├── MANIFEST.MF
│   └── web.xml
└── WEB-INF
    ├── classes
    │   ├── com
    │   │   └── test
    │   │       ├── domain
    │   │       │   └── Person.class
    │   │       └── web
    │   │           └── EventManagerServlet.class
    │   └── persistence.xml
    ├── lib
    │   ├── antlr-2.7.7.jar
    │   ├── dom4j-1.6.1.jar
    │   ├── hibernate-commons-annotations-4.0.4.Final.jar
    │   ├── hibernate-core-4.3.5.Final.jar
    │   ├── hibernate-jpa-2.1-api-1.0.0.Final.jar
    │   ├── jandex-1.1.0.Final.jar
    │   ├── javassist-3.18.1-GA.jar
    │   ├── javax.servlet-api-3.0.1.jar
    │   ├── jboss-logging-3.1.3.GA.jar
    │   ├── jboss-logging-annotations-1.2.0.Beta1.jar
    │   ├── jboss-transaction-api_1.2_spec-1.0.0.Final.jar
    │   ├── mysql-connector-java-5.1.13.jar
    │   └── xml-apis-1.0.b2.jar
    └── web.xml

EDIT

I had to add in the build.gradle

classpath 'org.hibernate:hibernate-entitymanager:4.1.7.Final'

Answer 1

The persistence.xml file needs to go into the War's WEB-INF/classes/META-INF/ directory. The best way to accomplish this is to put it into src/main/resources/META-INF/. If you also want this to work in tests (which run off class directories rather than a Jar or War), you additionally need to configure:

sourceSets.all {
    output.resourcesDir = output.classesDir
}

Above configuration is required because JPA expects to find the persistence.xml file and the corresponding entity classes in the same class directory or archive, but Gradle defaults to using different output directories for classes and resources.

PS: I assume the main directory is under src, not a sibling of src as shown in your first diagram.