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<!doctype html>
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Java - 非著名Java程序员
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<h1>Spring事务管理</h1>
<div class="a-content">
<div class="a-content-text">
<p><code>@Transactional</code> 保证事务一致性。<br />
当出现异常时，会回滚</p>
<p>隔离级别：<br />
隔离级别是指多个并发事务之间的隔离程度。与开发相关的场景主要包括：脏读取、重复读、幻读。</p>
<pre class="line-numbers"><code class="language-plain_text">package org.springframework.transaction.annotation;
public enum Isolation {
DEFAULT(-1),
READ_UNCOMMITTED(1),
READ_COMMITTED(2),
REPEATABLE_READ(4),
SERIALIZABLE(8);
private final int value;
private Isolation(int value) {
this.value = value;
}
public int value() {
return this.value;
}
}
</code></pre>
<p>Isolation枚举类中定义了5个表示隔离级别的值</p>
<p>DEFAULT 默认值，表示使用底层数据库的默认隔离级别。对大部分数据库而言，就是READ_COMMITED</p>
<p>READ_UNCOMMITED：该隔离级别表示，一个事务可以读取另一个事务修改但是还未提交的数据。不能防止脏读和不可重复读。很少使用。</p>
<p>READ_COMMITED:该隔离级别表示，只能读取另一个事务已经提交的数据。该事务级别可以防止脏读，也是大多数情况下的推荐值。</p>
<p>REPEATABLE_READ:该隔离级别表示一个事务在整个过程中可以多次重复执行某个查询，并返回相同结果。在多次查询之间有新增的值会被忽略。可以防止不可重复读和脏读。</p>
<p>SERIALIZABLE：所有的事务依次逐个执行，这样事务之间就完全不可能产生干扰，也就是说，该级别可以防止脏读、不可重复读以及幻读。但是这将严重影响程序的性能。通常情况下也不会用到该级别</p>
<p>指定方法：</p>
<pre class="line-numbers"><code class="language-plain_text">@Transactional(isolation = Isolation.DEFAULT)
</code></pre>
<p>传播行为：</p>
<pre class="line-numbers"><code class="language-plain_text">package org.springframework.transaction.annotation;
public enum Propagation {
REQUIRED(0),
SUPPORTS(1),
MANDATORY(2),
REQUIRES_NEW(3),
NOT_SUPPORTED(4),
NEVER(5),
NESTED(6);
private final int value;
private Propagation(int value) {
this.value = value;
}
public int value() {
return this.value;
}
}
</code></pre>
<p>Propagation枚举类中定义了6个表示传播行为的枚举值：<br />
REQUIRED：如果当前存在事务，则加入该事务；如果当前没有事务，则创建一个新的事务。<br />
SUPPORTS：如果当前存在事务，则加入该事务；如果当前没有事务，则以非事务的方式继续运行。<br />
MANDATORY：如果当前存在事务，则加入该事务；如果当前没有事务，则抛出异常。<br />
REQUIRES_NEW：创建一个新的事务，如果当前存在事务，则把当前事务挂起。<br />
NOT_SUPPORTED：以非事务方式运行，如果当前存在事务，则把当前事务挂起。<br />
NEVER：以非事务方式运行，如果当前存在事务，则抛出异常。<br />
NESTED：如果当前存在事务，则创建一个事务作为当前事务的嵌套事务来运行；如果当前没有事务，则该取值等价于REQUIRED</p>
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<span class="date">2020/10/21 20:09 下午</span>
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