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Java example source code file (JpaLocalTxnInterceptor.java)

This example Java source code file (JpaLocalTxnInterceptor.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

class, entitymanager, entitytransaction, exception, inject, internal, jpalocaltxninterceptor, jpapersistservice, methodinterceptor, object, reflection, threadlocal, throwable, transactional, unitofwork

The JpaLocalTxnInterceptor.java Java example source code

/**
 * Copyright (C) 2010 Google, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.inject.persist.jpa;

import com.google.inject.Inject;
import com.google.inject.persist.Transactional;
import com.google.inject.persist.UnitOfWork;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

import java.lang.reflect.Method;

import javax.persistence.EntityManager;
import javax.persistence.EntityTransaction;

/**
 * @author Dhanji R. Prasanna (dhanji@gmail.com)
 */
class JpaLocalTxnInterceptor implements MethodInterceptor {

  // TODO(gak): Move these args to the cxtor & make these final.
  @Inject
  private JpaPersistService emProvider = null;

  @Inject
  private UnitOfWork unitOfWork = null;

  @Transactional
  private static class Internal {}

  // Tracks if the unit of work was begun implicitly by this transaction.
  private final ThreadLocal<Boolean> didWeStartWork = new ThreadLocal();

  public Object invoke(MethodInvocation methodInvocation) throws Throwable {

    // Should we start a unit of work?
    if (!emProvider.isWorking()) {
      emProvider.begin();
      didWeStartWork.set(true);
    }

    Transactional transactional = readTransactionMetadata(methodInvocation);
    EntityManager em = this.emProvider.get();

    // Allow 'joining' of transactions if there is an enclosing @Transactional method.
    if (em.getTransaction().isActive()) {
      return methodInvocation.proceed();
    }

    final EntityTransaction txn = em.getTransaction();
    txn.begin();

    Object result;
    try {
      result = methodInvocation.proceed();

    } catch (Exception e) {
      //commit transaction only if rollback didnt occur
      if (rollbackIfNecessary(transactional, e, txn)) {
        txn.commit();
      }

      //propagate whatever exception is thrown anyway
      throw e;
    } finally {
      // Close the em if necessary (guarded so this code doesn't run unless catch fired).
      if (null != didWeStartWork.get() && !txn.isActive()) {
        didWeStartWork.remove();
        unitOfWork.end();
      }
    }

    //everything was normal so commit the txn (do not move into try block above as it
    //  interferes with the advised method's throwing semantics)
    try {
      txn.commit();
    } finally {
      //close the em if necessary
      if (null != didWeStartWork.get() ) {
        didWeStartWork.remove();
        unitOfWork.end();
      }
    }

    //or return result
    return result;
  }

  // TODO(dhanji): Cache this method's results.
  private Transactional readTransactionMetadata(MethodInvocation methodInvocation) {
    Transactional transactional;
    Method method = methodInvocation.getMethod();
    Class<?> targetClass = methodInvocation.getThis().getClass();

    transactional = method.getAnnotation(Transactional.class);
    if (null == transactional) {
      // If none on method, try the class.
      transactional = targetClass.getAnnotation(Transactional.class);
    }
    if (null == transactional) {
      // If there is no transactional annotation present, use the default
      transactional = Internal.class.getAnnotation(Transactional.class);
    }

    return transactional;
  }

  /**
   * Returns True if rollback DID NOT HAPPEN (i.e. if commit should continue).
   *
   * @param transactional The metadata annotaiton of the method
   * @param e The exception to test for rollback
   * @param txn A JPA Transaction to issue rollbacks on
   */
  private boolean rollbackIfNecessary(Transactional transactional, Exception e,
      EntityTransaction txn) {
    boolean commit = true;

    //check rollback clauses
    for (Class<? extends Exception> rollBackOn : transactional.rollbackOn()) {

      //if one matched, try to perform a rollback
      if (rollBackOn.isInstance(e)) {
        commit = false;

        //check ignore clauses (supercedes rollback clause)
        for (Class<? extends Exception> exceptOn : transactional.ignore()) {
          //An exception to the rollback clause was found, DON'T rollback
          // (i.e. commit and throw anyway)
          if (exceptOn.isInstance(e)) {
            commit = true;
            break;
          }
        }

        //rollback only if nothing matched the ignore check
        if (!commit) {
          txn.rollback();
        }
        //otherwise continue to commit

        break;
      }
    }

    return commit;
  }
}

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