Java分布式锁之数据库实现

<div id="cnblogs\_post\_body" class="blogpost-body">之前的文章<a href="http://www.cnblogs.com/garryfu/p/7978611.html" target="\_blank">《Java分布式锁实现》</a>中列举了分布式锁的3种实现方式，分别是基于数据库实现，基于缓存实现和基于zookeeper实现。三种实现方式各有可取之处，本篇文章就详细讲解一下Java分布式锁之基于数据库的实现方式，也是最简单最易理解的实现方式。 首先，先来阐述下“锁”的概念，锁作为一种安全防御工具，既能上锁防止别人打开，又能让持有钥匙的人打开锁，这是锁的基本功能。那再来说一下“分布式锁”，分布式锁是在分布式系统(多个独立运行系统)内的锁，相对来说，这把锁的安全级别以及作用范围更大，所以从设计上就要考虑更多东西。 现在来说，怎么基于数据库实现这把分布式锁。其实说白了就是，把锁作为数据资源存入数据库，当持有这把锁的访问者来决定是否开锁。以下详细讲解了数据库的交易同步锁和交易重试补偿锁的实现。 <h4>一、数据库的设计</h4> 数据库锁表的表结构如下： <table style="height: 249px; width: 668px" border="1" align="center"><caption> </caption> <thead> <tr style="background-color: #9cd2d3" dir="ltr"> <td>field</td> <td>type</td> <td>comment</td> </tr> </thead> <tbody> <tr> <td>ID</td> <td>bigint</td> <td>主键</td> </tr> <tr> <td>OUTER\_SERIAL\_NO</td> <td>varchar</td> <td>流水号</td> </tr> <tr> <td>CUST\_NO</td> <td>char</td> <td>客户号</td> </tr> <tr> <td>SOURCE\_CODE</td> <td>varchar</td> <td>锁操作</td> </tr> <tr> <td>THREAD\_NO</td> <td>varchar</td> <td>线程号</td> </tr> <tr> <td>STATUS</td> <td>char</td> <td>锁状态</td> </tr> <tr> <td>REMARK</td> <td>varchar</td> <td>备注</td> </tr> <tr> <td>CREATED\_AT</td> <td>timestamp</td> <td>创建时间</td> </tr> <tr> <td>UPDATED\_AT</td> <td>timestamp</td> <td>更新时间</td> </tr> </tbody> </table> 作为锁的必要属性有5个：系统流水号，客户号，锁操作，线程号和锁状态，下面来解释一下每种属性 流水号：锁的具体指向，比如可以是产品，可以是交易流水号（后面会说到交易同步锁、交易补偿锁的使用方式） 客户号：客户的唯一标识 锁操作：客户的某种操作，比如客户取现操作，取现补偿重试操作 线程号：当前操作线程的线程号，比如取当前线程的uuid 锁状态：P处理中，F失败，Y成功 <h4>二、代码设计</h4> 代码的目录结构如下：  <img src="https://images2017.cnblogs.com/blog/1289521/201712/1289521-20171212153515566-1626398048.png" alt="" width="178" height="231"> 主要贴一下锁操作的核心代码实现： 锁接口定义：DbLockManager.java <div class="cnblogs\_code"><img id="code\_img\_closed\_f2ef6495-555e-4615-bbd9-f8bf37e75ba2" class="code\_img\_closed" src="https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif" alt="" style="display: inline;"><img id="code\_img\_opened\_f2ef6495-555e-4615-bbd9-f8bf37e75ba2" class="code\_img\_opened" style="display: none;" src="https://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif" alt=""> <div id="cnblogs\_code\_open\_f2ef6495-555e-4615-bbd9-f8bf37e75ba2" class="cnblogs\_code\_hide" style="display: none;"><div class="cnblogs\_code\_toolbar"><a href="javascript:void(0);" onclick="copyCnblogsCode(this)" title="复制代码"><img src="https://my.oschina.net//common.cnblogs.com/images/copycode.gif" alt="复制代码"></a></div> <pre>/\*\* \* 锁接口 \* \* @Author fugaoyang \* \*/ public interface DbLockManager {

1</span><span style="color: #008000">/**</span><span style="color: #008000">
2 * 加锁
3 </span><span style="color: #008000">*/</span>
4<span style="color: #0000ff">boolean</span><span style="color: #000000"> lock(String outerSerialNo, String custNo, LockSource source);
5
6</span><span style="color: #008000">/**</span><span style="color: #008000">
7 * 解锁
8 </span><span style="color: #008000">*/</span>
9<span style="color: #0000ff">void</span><span style="color: #000000"> unLock(String outerSerialNo, String custNo, LockSource source, LockStatus targetStatus);

}</pre>

<div class="cnblogs\_code\_toolbar"><a href="javascript:void(0);" onclick="copyCnblogsCode(this)" title="复制代码"><img src="https://my.oschina.net//common.cnblogs.com/images/copycode.gif" alt="复制代码"></a></div></div> View Code</div> 锁接口实现类：DbLockManagerImpl.java <div class="cnblogs\_code"><img id="code\_img\_closed\_e79c666f-0f72-4273-add4-9382bc8c369c" class="code\_img\_closed" src="https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif" alt=""><img id="code\_img\_opened\_e79c666f-0f72-4273-add4-9382bc8c369c" class="code\_img\_opened" style="display: none" src="https://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif" alt=""> <div id="cnblogs\_code\_open\_e79c666f-0f72-4273-add4-9382bc8c369c" class="cnblogs\_code\_hide"> <pre>/\*\* \* \* 数据库锁实现 \* \* @author fugaoyang \* \*/ @Service public class DbLockManagerImpl implements DbLockManager {

1</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">final</span> Logger LOG = LoggerFactory.getLogger(<span style="color: #0000ff">this</span><span style="color: #000000">.getClass());
2
3@Autowired
4</span><span style="color: #0000ff">private</span><span style="color: #000000"> DbSyncLockMapper lockMapper;
5
6@Transactional
7</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">boolean</span><span style="color: #000000"> lock(String outerSerialNo, String custNo, LockSource source) {
8
9    </span><span style="color: #0000ff">boolean</span> isLock = <span style="color: #0000ff">false</span><span style="color: #000000">;
10    TradeSyncLock lock </span>= <span style="color: #0000ff">null</span><span style="color: #000000">;
11    </span><span style="color: #0000ff">try</span><span style="color: #000000"> {
12        lock </span>=<span style="color: #000000"> lockMapper.find(outerSerialNo, custNo, source.getCode());
13
14        </span><span style="color: #0000ff">if</span> (<span style="color: #0000ff">null</span> ==<span style="color: #000000"> lock) {
15            lock </span>= <span style="color: #0000ff">new</span><span style="color: #000000"> TradeSyncLock();
16            createLock(lock, outerSerialNo, custNo, source);
17
18            </span><span style="color: #0000ff">int</span> num =<span style="color: #000000"> lockMapper.insert(lock);
19            </span><span style="color: #0000ff">if</span> (num == 1<span style="color: #000000">) {
20                isLock </span>= <span style="color: #0000ff">true</span><span style="color: #000000">;
21            }
22
23            LOG.info(ThreadLogUtils.getLogPrefix() </span>+ "加入锁，客户号[{}]，锁类型[{}]"<span style="color: #000000">, custNo, source.getCode());
24            </span><span style="color: #0000ff">return</span><span style="color: #000000"> isLock;
25        }
26
27        </span><span style="color: #008000">//</span><span style="color: #008000"> 根据交易类型进行加锁</span>
28        isLock =<span style="color: #000000"> switchSynsLock(lock, source);
29        LOG.info(ThreadLogUtils.getLogPrefix() </span>+ "更新锁，客户号[{}]，锁类型[{}]"<span style="color: #000000">, custNo, source.getCode());
30
31    } </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (Exception e) {
32        LOG.error(ThreadLogUtils.getLogPrefix() </span>+ "交易加锁异常, 客户号：" +<span style="color: #000000"> custNo, e);
33    }
34    </span><span style="color: #0000ff">return</span><span style="color: #000000"> isLock;
35}
36
37@Transactional
38</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">void</span><span style="color: #000000"> unLock(String outerSerialNo, String custNo, LockSource source, LockStatus targetStatus) {
39
40    </span><span style="color: #0000ff">try</span><span style="color: #000000"> {
41        TradeSyncLock lock </span>=<span style="color: #000000"> lockMapper.find(outerSerialNo, custNo, source.getCode());
42
43        </span><span style="color: #0000ff">if</span> (<span style="color: #0000ff">null</span> !=<span style="color: #000000"> lock) {
44            lockMapper.update(lock.getId(), targetStatus.getName(), LockStatus.P.getName(),
45                    ThreadLogUtils.getCurrThreadUuid(), ThreadLogUtils.getCurrThreadUuid());
46        }
47
48        LOG.info(ThreadLogUtils.getLogPrefix() </span>+ "释放锁，客户号[{}]，锁类型[{}]"<span style="color: #000000">, custNo, source.getCode());
49    } </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (Exception e) {
50        LOG.error(ThreadLogUtils.getLogPrefix() </span>+ "释放锁异常, 客户号：{}"<span style="color: #000000">, custNo, e);
51    }
52}
53
54</span><span style="color: #008000">/**</span><span style="color: #008000">
55 * 匹配加锁
56 </span><span style="color: #008000">*/</span>
57<span style="color: #0000ff">private</span> <span style="color: #0000ff">boolean</span><span style="color: #000000"> switchSynsLock(TradeSyncLock lock, LockSource source) {
58    </span><span style="color: #0000ff">boolean</span> isLock = <span style="color: #0000ff">false</span><span style="color: #000000">;
59
60    </span><span style="color: #0000ff">switch</span><span style="color: #000000"> (source) {
61    </span><span style="color: #0000ff">case</span><span style="color: #000000"> WITHDRAW:
62        ;
63        isLock </span>=<span style="color: #000000"> tradeSynsLock(lock);
64        </span><span style="color: #0000ff">break</span><span style="color: #000000">;
65    </span><span style="color: #0000ff">case</span><span style="color: #000000"> WITHDRAW_RETRY:
66        ;
67        isLock </span>=<span style="color: #000000"> retrySynsLock(lock);
68        </span><span style="color: #0000ff">break</span><span style="color: #000000">;
69    </span><span style="color: #0000ff">default</span><span style="color: #000000">:
70        ;
71    }
72    </span><span style="color: #0000ff">return</span><span style="color: #000000"> isLock;
73}
74
75</span><span style="color: #008000">/**</span><span style="color: #008000">
76 * 交易同步锁
77 </span><span style="color: #008000">*/</span>
78<span style="color: #0000ff">private</span> <span style="color: #0000ff">boolean</span><span style="color: #000000"> tradeSynsLock(TradeSyncLock lock) {
79    </span><span style="color: #008000">//</span><span style="color: #008000"> 处理中的不加锁，即不执行交易操作</span>
80    <span style="color: #0000ff">if</span><span style="color: #000000"> (LockStatus.P.getName().equals(lock.getStatus())) {
81        </span><span style="color: #0000ff">return</span> <span style="color: #0000ff">false</span><span style="color: #000000">;
82    }
83
84    </span><span style="color: #0000ff">int</span> num =<span style="color: #000000"> lockMapper.update(lock.getId(), LockStatus.P.getName(), LockStatus.S.getName(),
85            ThreadLogUtils.getCurrThreadUuid(), </span><span style="color: #0000ff">null</span><span style="color: #000000">);
86    </span><span style="color: #0000ff">if</span> (num == 1<span style="color: #000000">) {
87        </span><span style="color: #0000ff">return</span> <span style="color: #0000ff">true</span><span style="color: #000000">;
88    }
89    </span><span style="color: #0000ff">return</span> <span style="color: #0000ff">false</span><span style="color: #000000">;
90}
91
92</span><span style="color: #008000">/**</span><span style="color: #008000">
93 * 补偿同步锁
94 </span><span style="color: #008000">*/</span>
95<span style="color: #0000ff">private</span> <span style="color: #0000ff">boolean</span><span style="color: #000000"> retrySynsLock(TradeSyncLock lock) {
96    </span><span style="color: #008000">//</span><span style="color: #008000"> 处理中或处理完成的不加锁，即不执行补偿操作</span>
97    <span style="color: #0000ff">if</span> (LockStatus.P.getName().equals(lock.getStatus()) ||<span style="color: #000000"> LockStatus.S.getName().equals(lock.getStatus())) {
98        </span><span style="color: #0000ff">return</span> <span style="color: #0000ff">false</span><span style="color: #000000">;
99    }
100
101    </span><span style="color: #0000ff">int</span> num =<span style="color: #000000"> lockMapper.update(lock.getId(), LockStatus.P.getName(), LockStatus.F.getName(),
102            ThreadLogUtils.getCurrThreadUuid(), </span><span style="color: #0000ff">null</span><span style="color: #000000">);
103    </span><span style="color: #0000ff">if</span> (num == 1<span style="color: #000000">) {
104        </span><span style="color: #0000ff">return</span> <span style="color: #0000ff">true</span><span style="color: #000000">;
105    }
106    </span><span style="color: #0000ff">return</span> <span style="color: #0000ff">false</span><span style="color: #000000">;
107}
108
109</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">void</span><span style="color: #000000"> createLock(TradeSyncLock lock, String outerSerialNo, String custNo, LockSource source) {
110    lock.setOuterSerialNo(outerSerialNo);
111    lock.setCustNo(custNo);
112    lock.setSourceCode(source.getCode());
113    lock.setThreadNo(ThreadLogUtils.getCurrThreadUuid());
114    lock.setStatus(LockStatus.P.getName());
115    lock.setRemark(source.getDesc());
116}

}</pre>

</div> View Code</div> 获取当前线程号以及打印uuid工具类ThreadLogUtils.Java <div class="cnblogs\_code"><img id="code\_img\_closed\_25ad7b32-da05-4059-b8e6-077baabc33d8" class="code\_img\_closed" src="https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif" alt=""><img id="code\_img\_opened\_25ad7b32-da05-4059-b8e6-077baabc33d8" class="code\_img\_opened" style="display: none" src="https://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif" alt=""> <div id="cnblogs\_code\_open\_25ad7b32-da05-4059-b8e6-077baabc33d8" class="cnblogs\_code\_hide"> <pre>/\*\* \* \* 线程处理 \* \* @author fugaoyang \* \*/ public class ThreadLogUtils {

1</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> ThreadLogUtils instance = <span style="color: #0000ff">null</span><span style="color: #000000">;
2
3</span><span style="color: #0000ff">private</span><span style="color: #000000"> ThreadLogUtils() {
4    setInstance(</span><span style="color: #0000ff">this</span><span style="color: #000000">);
5}
6
7</span><span style="color: #008000">//</span><span style="color: #008000"> 初始化标志</span>
8<span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">final</span> Object __noop = <span style="color: #0000ff">new</span><span style="color: #000000"> Object();
9</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> ThreadLocal&lt;Object&gt; __flag = <span style="color: #0000ff">new</span> InheritableThreadLocal&lt;Object&gt;<span style="color: #000000">() {
10    @Override
11    </span><span style="color: #0000ff">protected</span><span style="color: #000000"> Object initialValue() {
12        </span><span style="color: #0000ff">return</span> <span style="color: #0000ff">null</span><span style="color: #000000">;
13    }
14};
15
16</span><span style="color: #008000">//</span><span style="color: #008000"> 当前线程的UUID信息，主要用于打印日志；</span>
17<span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> ThreadLocal&lt;String&gt; currLogUuid = <span style="color: #0000ff">new</span> InheritableThreadLocal&lt;String&gt;<span style="color: #000000">() {
18    @Override
19    </span><span style="color: #0000ff">protected</span><span style="color: #000000"> String initialValue() {
20        </span><span style="color: #0000ff">return</span> UUID.randomUUID().toString()<span style="color: #008000">/*</span><span style="color: #008000"> .toUpperCase() </span><span style="color: #008000">*/</span><span style="color: #000000">;
21    }
22};
23
24</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> ThreadLocal&lt;String&gt; currThreadUuid = <span style="color: #0000ff">new</span> ThreadLocal&lt;String&gt;<span style="color: #000000">() {
25    @Override
26    </span><span style="color: #0000ff">protected</span><span style="color: #000000"> String initialValue() {
27        </span><span style="color: #0000ff">return</span><span style="color: #000000"> UUIDGenerator.getUuid();
28    }
29};
30
31</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> clear(Boolean isNew) {
32    </span><span style="color: #0000ff">if</span><span style="color: #000000"> (isNew) {
33
34        currLogUuid.remove();
35
36        __flag.remove();
37
38        currThreadUuid.remove();
39
40    }
41}
42
43</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span><span style="color: #000000"> String getCurrLogUuid() {
44    </span><span style="color: #0000ff">if</span> (!<span style="color: #000000">isInitialized()) {
45        </span><span style="color: #0000ff">throw</span> <span style="color: #0000ff">new</span> IllegalStateException("TLS未初始化"<span style="color: #000000">);
46    }
47
48    </span><span style="color: #0000ff">return</span><span style="color: #000000"> currLogUuid.get();
49}
50
51</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span><span style="color: #000000"> String getCurrThreadUuid() {
52    </span><span style="color: #0000ff">return</span><span style="color: #000000"> currThreadUuid.get();
53}
54
55</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> clearCurrThreadUuid() {
56    currThreadUuid.remove();
57}
58
59</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span><span style="color: #000000"> String getLogPrefix() {
60    </span><span style="color: #0000ff">if</span> (!<span style="color: #000000">isInitialized()) {
61        </span><span style="color: #0000ff">return</span> ""<span style="color: #000000">;
62    }
63
64    </span><span style="color: #0000ff">return</span> "&lt;uuid=" + getCurrLogUuid() + "&gt;"<span style="color: #000000">;
65}
66
67</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">boolean</span><span style="color: #000000"> isInitialized() {
68    </span><span style="color: #0000ff">return</span> __flag.get() != <span style="color: #0000ff">null</span><span style="color: #000000">;
69}
70
71</span><span style="color: #008000">/**</span><span style="color: #008000">
72 * 初始化上下文，如果已经初始化则返回false，否则返回true&lt;br/&gt;
73 *
74 * </span><span style="color: #808080">@return</span>
75 <span style="color: #008000">*/</span>
76<span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">boolean</span><span style="color: #000000"> initialize() {
77    </span><span style="color: #0000ff">if</span><span style="color: #000000"> (isInitialized()) {
78        </span><span style="color: #0000ff">return</span> <span style="color: #0000ff">false</span><span style="color: #000000">;
79    }
80
81    __flag.set(__noop);
82    </span><span style="color: #0000ff">return</span> <span style="color: #0000ff">true</span><span style="color: #000000">;
83}
84
85</span><span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> setInstance(ThreadLogUtils instance) {
86    ThreadLogUtils.instance </span>=<span style="color: #000000"> instance;
87}
88
89</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span><span style="color: #000000"> ThreadLogUtils getInstance() {
90    </span><span style="color: #0000ff">return</span><span style="color: #000000"> instance;
91}

}</pre>

</div> View Code</div> 两种锁的实现的大致思路如下： 1.交易同步锁 当一个客户来取现，第一次进入时，会插入一条当前线程，状态是P，操作是取现的锁，取现成功后根据当前线程号会更新成功； 当一个客户同时多个取现操作时，只有一个取现操作会加锁成功，其它会加锁失败； 当一个客户已经在取现中，这时数据库已经有一条状态P的锁，该客户同时又做了取现，这个取现动作会尝试加锁而退出； 2.交易重试补偿锁 1.当一个客户取现加锁成功，因调用第三方支付接口超时时，后台会对该笔交易重新发起重试打款操作，这时会新加一条当前交易流水号，当前线程号，状态是P，操作是取现重试的锁，重试的支付结果是成功的话，更新该条锁数据为Y状态，否则更新该条数据为F状态； 2.当重试支付失败后，再去重试打款时，发现锁的状态是F，这时把F更新为P，继续重试，根据重试结果更新锁状态。 上面实现的是一个最基本的数据库分布式锁，满足的并发量也是基于数据库所能扛得住的，性能基本可以满足普通的交易量。 后续可以优化的部分： 1.当一个用户同时多次获取lock时，因为目前是用的乐观锁，只会有一个加锁成功，可以优化成加入while(true)循环获取lock，当失败次数到达指定次数时退出，当前的操作结束。 2.当锁表数据量随着时间增大时，可以考虑按用户对锁表进行分表分库，以减小数据库方面的压力。 3.对锁的操作可以抽象出来，作为抽象实现，比如具体的取现操作只关心取现这个业务实现。   因为时间有限，写的比较仓促，希望大家有问题可以提出，相互探讨~~ 完整示例代码后续会更新到github。   <style>p.p1 { margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Monaco }</style> <style>p.p1 { margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Monaco }</style> <style>p.p1 { margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Monaco }</style></div>

Java分布式锁之数据库实现

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