Flowable源码注释（二十八）流程定义缓存实现类

Flowable源码地址：https://github.com/flowable/flowable-engine

Flowable-6.7.2 源码注释地址：https://github.com/solojin/flowable-6.7.2-annotated

包路径：org.flowable.engine.impl.persistence.deploy

ProcessDefinitionInfoCache 流程定义缓存实现类

/**
* 默认缓存：将所有内容保留在内存中，除非设置了限制。
* 用Map结构存储缓存信息，缓存实体为ProcessDefinitionInfoCacheObject流程定义缓存对象
*
* @author Tijs Rademakers
*/
public class ProcessDefinitionInfoCache implements DeploymentCache<ProcessDefinitionInfoCacheObject> {
private static final Logger LOGGER = LoggerFactory.getLogger(ProcessDefinitionInfoCache.class);
protected Map<String, ProcessDefinitionInfoCacheObject> cache;
protected CommandExecutor commandExecutor;
/** 不做限制的缓存 */
public ProcessDefinitionInfoCache(CommandExecutor commandExecutor) {
this.commandExecutor = commandExecutor;
// 译者注：Collections.synchronizedMap的同步Map方法效率比较低，因为内部使用的是Synchronized锁，推荐使用JUC包下的ConcurrentHashMap实现
this.cache = Collections.synchronizedMap(new HashMap<>());
}
/** 具有硬限制的缓存：缓存的元素数量不会超过int limit该限制。 */
public ProcessDefinitionInfoCache(CommandExecutor commandExecutor, final int limit) {
this.commandExecutor = commandExecutor;
// 译者注：Collections.synchronizedMap的同步Map方法效率比较低，因为内部使用的是Synchronized锁，推荐使用JUC包下的ConcurrentHashMap实现
this.cache = Collections.synchronizedMap(new LinkedHashMap<String, ProcessDefinitionInfoCacheObject>(limit + 1, 0.75f, true) {
// +1是必需的，因为在删除条目之前先插入该条目
// 加载因子默认值为0.75（参见javadocs）
// true将保留“访问顺序”，这是实现LRU缓存算法（即最近最少使用页面置换算法）所需的字段
private static final long serialVersionUID = 1L;
@Override
protected boolean removeEldestEntry(Map.Entry<String, ProcessDefinitionInfoCacheObject> eldest) {
boolean removeEldest = size() > limit;
if (removeEldest) {
// 已达到缓存限制，{}将被逐出
LOGGER.trace("Cache limit is reached, {} will be evicted", eldest.getKey());
}
return removeEldest;
}
});
}
@Override
public ProcessDefinitionInfoCacheObject get(final String processDefinitionId) {
ProcessDefinitionInfoCacheObject infoCacheObject = null;
Command<ProcessDefinitionInfoCacheObject> cacheCommand = new Command<ProcessDefinitionInfoCacheObject>() {
@Override
public ProcessDefinitionInfoCacheObject execute(CommandContext commandContext) {
return retrieveProcessDefinitionInfoCacheObject(processDefinitionId, commandContext);
}
};
if (Context.getCommandContext() != null) {
infoCacheObject = retrieveProcessDefinitionInfoCacheObject(processDefinitionId, Context.getCommandContext());
} else {
infoCacheObject = commandExecutor.execute(cacheCommand);
}
return infoCacheObject;
}
@Override
public boolean contains(String id) {
return cache.containsKey(id);
}
@Override
public void add(String id, ProcessDefinitionInfoCacheObject obj) {
cache.put(id, obj);
}
@Override
public void remove(String id) {
cache.remove(id);
}
@Override
public void clear() {
cache.clear();
}
@Override
public Collection<ProcessDefinitionInfoCacheObject> getAll() {
return cache.values();
}
@Override
public int size() {
return cache.size();
}
protected ProcessDefinitionInfoCacheObject retrieveProcessDefinitionInfoCacheObject(String processDefinitionId, CommandContext commandContext) {
ProcessDefinitionInfoEntityManager infoEntityManager = CommandContextUtil.getProcessDefinitionInfoEntityManager(commandContext);
ObjectMapper objectMapper = CommandContextUtil.getProcessEngineConfiguration(commandContext).getObjectMapper();
ProcessDefinitionInfoCacheObject cacheObject = null;
if (cache.containsKey(processDefinitionId)) {
cacheObject = cache.get(processDefinitionId);
} else {
cacheObject = new ProcessDefinitionInfoCacheObject();
cacheObject.setRevision(0);
cacheObject.setInfoNode(objectMapper.createObjectNode());
}
ProcessDefinitionInfoEntity infoEntity = infoEntityManager.findProcessDefinitionInfoByProcessDefinitionId(processDefinitionId);
if (infoEntity != null && infoEntity.getRevision() != cacheObject.getRevision()) {
cacheObject.setRevision(infoEntity.getRevision());
if (infoEntity.getInfoJsonId() != null) {
byte[] infoBytes = infoEntityManager.findInfoJsonById(infoEntity.getInfoJsonId());
try {
ObjectNode infoNode = (ObjectNode) objectMapper.readTree(infoBytes);
cacheObject.setInfoNode(infoNode);
} catch (Exception e) {
// 读取进程定义的json info节点时出错
throw new FlowableException("Error reading json info node for process definition " + processDefinitionId, e);
}
}
} else if (infoEntity == null) {
cacheObject.setRevision(0);
cacheObject.setInfoNode(objectMapper.createObjectNode());
}
return cacheObject;
}
}

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