Spring中事务传播特性（Propagation）

先来看一下Transactional源码，

package org.springframework.transaction.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.core.annotation.AliasFor;

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Transactional {
    @AliasFor("transactionManager")
    String value() default "";

    @AliasFor("value")
    String transactionManager() default "";

    Propagation propagation() default Propagation.REQUIRED;

    Isolation isolation() default Isolation.DEFAULT;

    int timeout() default -1;

    boolean readOnly() default false;

    Class<? extends Throwable>[] rollbackFor() default {};

    String[] rollbackForClassName() default {};

    Class<? extends Throwable>[] noRollbackFor() default {};

    String[] noRollbackForClassName() default {};
}

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其中定义了事务的传播特性Propagation

接下来我们看一下Propagation源码

/**
 * Enumeration that represents transaction propagation behaviors for use
 * with the {@link Transactional} annotation, corresponding to the
 * {@link TransactionDefinition} interface.
 *
 * @author Colin Sampaleanu
 * @author Juergen Hoeller
 * @since 1.2
 */
public enum Propagation {

	/**
	 * Support a current transaction, create a new one if none exists.
	 * Analogous to EJB transaction attribute of the same name.
	 * 
This is the default setting of a transaction annotation.
	 */
	REQUIRED(TransactionDefinition.PROPAGATION_REQUIRED),

	/**
	 * Support a current transaction, execute non-transactionally if none exists.
	 * Analogous to EJB transaction attribute of the same name.
	 * 
Note: For transaction managers with transaction synchronization,
	 * {@code SUPPORTS} is slightly different from no transaction at all,
	 * as it defines a transaction scope that synchronization will apply for.
	 * As a consequence, the same resources (JDBC Connection, Hibernate Session, etc)
	 * will be shared for the entire specified scope. Note that this depends on
	 * the actual synchronization configuration of the transaction manager.
	 * @see org.springframework.transaction.support.AbstractPlatformTransactionManager#setTransactionSynchronization
	 */
	SUPPORTS(TransactionDefinition.PROPAGATION_SUPPORTS),

	/**
	 * Support a current transaction, throw an exception if none exists.
	 * Analogous to EJB transaction attribute of the same name.
	 */
	MANDATORY(TransactionDefinition.PROPAGATION_MANDATORY),

	/**
	 * Create a new transaction, and suspend the current transaction if one exists.
	 * Analogous to the EJB transaction attribute of the same name.
	 * 
NOTE: Actual transaction suspension will not work out-of-the-box
	 * on all transaction managers. This in particular applies to
	 * {@link org.springframework.transaction.jta.JtaTransactionManager},
	 * which requires the {@code javax.transaction.TransactionManager} to be
	 * made available to it (which is server-specific in standard Java EE).
	 * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
	 */
	REQUIRES_NEW(TransactionDefinition.PROPAGATION_REQUIRES_NEW),

	/**
	 * Execute non-transactionally, suspend the current transaction if one exists.
	 * Analogous to EJB transaction attribute of the same name.
	 * 
NOTE: Actual transaction suspension will not work out-of-the-box
	 * on all transaction managers. This in particular applies to
	 * {@link org.springframework.transaction.jta.JtaTransactionManager},
	 * which requires the {@code javax.transaction.TransactionManager} to be
	 * made available to it (which is server-specific in standard Java EE).
	 * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
	 */
	NOT_SUPPORTED(TransactionDefinition.PROPAGATION_NOT_SUPPORTED),

	/**
	 * Execute non-transactionally, throw an exception if a transaction exists.
	 * Analogous to EJB transaction attribute of the same name.
	 */
	NEVER(TransactionDefinition.PROPAGATION_NEVER),

	/**
	 * Execute within a nested transaction if a current transaction exists,
	 * behave like {@code REQUIRED} otherwise. There is no analogous feature in EJB.
	 * 
Note: Actual creation of a nested transaction will only work on specific
	 * transaction managers. Out of the box, this only applies to the JDBC
	 * DataSourceTransactionManager. Some JTA providers might support nested
	 * transactions as well.
	 * @see org.springframework.jdbc.datasource.DataSourceTransactionManager
	 */
	NESTED(TransactionDefinition.PROPAGATION_NESTED);


	private final int value;


	Propagation(int value) {
		this.value = value;
	}

	public int value() {
		return this.value;
	}

}

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Propagation是一个枚举类型，其中定了7种类型