先看下Spring的 事务传播行为类型
事务传播行为类型 | 说明 |
PROPAGATION_REQUIRED | 如果当前没有事务,就新建一个事务,如果已经存在一个事务中,加入到这个事务中。这是 最常见的选择。 |
PROPAGATION_SUPPORTS | 支持当前事务,如果当前没有事务,就以非事务方式执行。 |
PROPAGATION_MANDATORY | 使用当前的事务,如果当前没有事务,就抛出异常。 |
PROPAGATION_REQUIRES_NEW | 新建事务,如果当前存在事务,把当前事务挂起。 |
PROPAGATION_NOT_SUPPORTED | 以非事务方式执行操作,如果当前存在事务,就把当前事务挂起。 |
PROPAGATION_NEVER | 以非事务方式执行,如果当前存在事务,则抛出异常。 |
PROPAGATION_NESTED | 如果当前存在事务,则在嵌套事务内执行。如果当前没有事务,则执行与 PROPAGATION_REQUIRED 类似的操作。 |
当使用 PROPAGATION_NESTED 时, 底层的数据源必须基于 JDBC 3.0 ,并且实现者需要支持保存点事务机制。
readOnly
事务属性中的readOnly标志表示对应的事务应该被最优化为只读事务。这 是一个最优化提示
Timeout
在事务属性中还有定义“timeout”值的选项,指定事务超时为几秒。在JTA中,这将被简单地传递到J2EE服务器的事务协调程序,并据此得到相应的 解释。
在xml中的设置应该是 timeout_11 表示超时为11秒。。
为什么呢。。看下面的源码可知。。
Java代码
/**
* PropertyEditor for TransactionAttribute objects. Takes Strings of form
* <p><code>PROPAGATION_NAME,ISOLATION_NAME,readOnly,timeout_NNNN,+Exception1,-Exception2</code>
* <p>where only propagation code is required. For example:
* <p><code>PROPAGATION_MANDATORY,ISOLATION_DEFAULT</code>
*
* <p>The tokens can be in <strong>any</strong> order. Propagation and isolation codes
* must use the names of the constants in the TransactionDefinition class. Timeout values
* are in seconds. If no timeout is specified, the transaction manager will apply a default
* timeout specific to the particular transaction manager.
*
* <p>A "+" before an exception name substring indicates that
* transactions should commit even if this exception is thrown;
* a "-" that they should roll back.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @since 24.04.2003
* @see org.springframework.transaction.TransactionDefinition
* @see org.springframework.core.Constants
*/
public class TransactionAttributeEditor extends PropertyEditorSupport {
/**
* Format is PROPAGATION_NAME,ISOLATION_NAME,readOnly,timeout_NNNN,+Exception1,-Exception2.
* Null or the empty string means that the method is non transactional.
* @see java.beans.PropertyEditor#setAsText(java.lang.String)
*/
public void setAsText(String s) throws IllegalArgumentException {
if (s == null || "".equals(s)) {
setValue(null);
}
else {
// tokenize it with ","
String[] tokens = StringUtils.commaDelimitedListToStringArray(s);
RuleBasedTransactionAttribute attr = new RuleBasedTransactionAttribute();
for (int i = 0; i < tokens.length; i++) {
String token = tokens[i].trim();
if (token.startsWith(RuleBasedTransactionAttribute.PREFIX_PROPAGATION)) {
attr.setPropagationBehaviorName(token);
}
else if (token.startsWith(RuleBasedTransactionAttribute.PREFIX_ISOLATION)) {
attr.setIsolationLevelName(token);
}
else if (token.startsWith(RuleBasedTransactionAttribute.PREFIX_TIMEOUT)) {
String value = token.substring(DefaultTransactionAttribute.PREFIX_TIMEOUT.length());
attr.setTimeout(Integer.parseInt(value));
}
else if (token.equals(RuleBasedTransactionAttribute.READ_ONLY_MARKER)) {
attr.setReadOnly(true);
}
else if (token.startsWith(RuleBasedTransactionAttribute.PREFIX_COMMIT_RULE)) {
attr.getRollbackRules().add(new NoRollbackRuleAttribute(token.substring(1)));
}
else if (token.startsWith(RuleBasedTransactionAttribute.PREFIX_ROLLBACK_RULE)) {
attr.getRollbackRules().add(new RollbackRuleAttribute(token.substring(1)));
}
else {
throw new IllegalArgumentException("Illegal transaction attribute token: [" + token + "]");
}
}
setValue(attr);
}
}
}
/**
* PropertyEditor for TransactionAttribute objects. Takes Strings of form
* <p><code>PROPAGATION_NAME,ISOLATION_NAME,readOnly,timeout_NNNN,+Exception1,-Exception2</code>
* <p>where only propagation code is required. For example:
* <p><code>PROPAGATION_MANDATORY,ISOLATION_DEFAULT</code>
*
* <p>The tokens can be in <strong>any</strong> order. Propagation and isolation codes
* must use the names of the constants in the TransactionDefinition class. Timeout values
* are in seconds. If no timeout is specified, the transaction manager will apply a default
* timeout specific to the particular transaction manager.
*
* <p>A "+" before an exception name substring indicates that
* transactions should commit even if this exception is thrown;
* a "-" that they should roll back.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @since 24.04.2003
* @see org.springframework.transaction.TransactionDefinition
* @see org.springframework.core.Constants
*/
public class TransactionAttributeEditor extends PropertyEditorSupport {
/**
* Format is PROPAGATION_NAME,ISOLATION_NAME,readOnly,timeout_NNNN,+Exception1,-Exception2.
* Null or the empty string means that the method is non transactional.
* @see java.beans.PropertyEditor#setAsText(java.lang.String)
*/
public void setAsText(String s) throws IllegalArgumentException {
if (s == null || "".equals(s)) {
setValue(null);
}
else {
// tokenize it with ","
String[] tokens = StringUtils.commaDelimitedListToStringArray(s);
RuleBasedTransactionAttribute attr = new RuleBasedTransactionAttribute();
for (int i = 0; i < tokens.length; i++) {
String token = tokens[i].trim();
if (token.startsWith(RuleBasedTransactionAttribute.PREFIX_PROPAGATION)) {
attr.setPropagationBehaviorName(token);
}
else if (token.startsWith(RuleBasedTransactionAttribute.PREFIX_ISOLATION)) {
attr.setIsolationLevelName(token);
}
else if (token.startsWith(RuleBasedTransactionAttribute.PREFIX_TIMEOUT)) {
String value = token.substring(DefaultTransactionAttribute.PREFIX_TIMEOUT.length());
attr.setTimeout(Integer.parseInt(value));
}
else if (token.equals(RuleBasedTransactionAttribute.READ_ONLY_MARKER)) {
attr.setReadOnly(true);
}
else if (token.startsWith(RuleBasedTransactionAttribute.PREFIX_COMMIT_RULE)) {
attr.getRollbackRules().add(new NoRollbackRuleAttribute(token.substring(1)));
}
else if (token.startsWith(RuleBasedTransactionAttribute.PREFIX_ROLLBACK_RULE)) {
attr.getRollbackRules().add(new RollbackRuleAttribute(token.substring(1)));
}
else {
throw new IllegalArgumentException("Illegal transaction attribute token: [" + token + "]");
}
}
setValue(attr);
}
}
}
从上面可以看出 token.substring() 这个方法把前缀timeout_给去掉了。。所以只剩下11了
从源码可看出来,PREFIX_XXXX 大都是这样写的,但前缀却是写在后面的。。觉得是不是命名有点古怪了,应该是XXXX_PREFIX,害我分析了一段时间。不过在源码上面的解释倒很清 楚:
* PropertyEditor for TransactionAttribute objects. Takes Strings of form
* <p><code>PROPAGATION_NAME,ISOLATION_NAME,readOnly,timeout_NNNN,+Exception1,-Exception2</code>
* <p>where only propagation code is required. For example:
* <p><code>PROPAGATION_MANDATORY,ISOLATION_DEFAULT</code>
文笔不好。。就给出个实例,我想一看就该明白了。
Xml代码
<bean id="transactionInterceptor" class="org.springframework.transaction.interceptor.TransactionInterceptor">
<!-- 事务拦截器bean需要依赖注入一个事务管理器 -->
<property name="transactionManager" ref="transactionManager"/>
<property name="transactionAttributes">
<!-- 下面定义事务传播属性-->
<props>
<prop key="get*">PROPAGATION_REQUIRED,readOnly</prop>
<prop key="*">PROPAGATION_REQUIRED,timeout_11</prop>
</props>
</property>
</bean>
<bean id="transactionInterceptor" class="org.springframework.transaction.interceptor.TransactionInterceptor">
<!-- 事务拦截器bean需要依赖注入一个事务管理器 -->
<property name="transactionManager" ref="transactionManager"/>
<property name="transactionAttributes">
<!-- 下面定义事务传播属性-->
<props>
<prop key="get*">PROPAGATION_REQUIRED,readOnly</prop>
<prop key="*">PROPAGATION_REQUIRED,timeout_11</prop>
</props>
</property>
</bean>
总结先到这里。。等深入研究的时候再把写详细些。。。
事务隔离级别
数据库并发操作存在的异常情况:
1. 更新丢失(Lost update):
2. 脏读取(Dirty Reads):
3. 不可重复读取(Non-repeatable Reads):
4. 两次更新问题(Second lost updates problem):
5. 幻读(Phantom Reads):
为了避免上面出现几种情况在标准SQL规范中定义了4个事务隔离级别,不同隔离级别对事务处理不同 。
1.未授权读取(Read Uncommitted):
2. 授权读取(Read Committed):
3. 可重复读取(Repeatable Read):
4. 串行(Serializable):
隔离级别 更新丢失 脏读取 重复读取 幻读
未授权读取 N Y Y Y
授权读取 N N Y Y
可重复 读取 N N N Y
串行 N N N N