spring hadoop系列（五）---spring hadoop hbase之HbaseSynchronizationManager

一、源码如下
/**
* Synchronization manager handling the tracking of Hbase resources (specifically tables). Used either manually or through {@link HbaseInterceptor} to bind a table to the thread.
* Each subsequent call made through {@link HbaseTemplate} is aware of the table bound and will use it instead of retrieving a new instance.
* HbaseSynchronizationManager是作为hbase资源同步管理跟踪（特别是表）；可以通过手动管理；也可以结合HbaseInterceptor将table绑定thread
* 随后的操作可以通过表绑定，而不是再重新创建新的对象
* @author Costin Leau
*/
public abstract class HbaseSynchronizationManager {

private static final Log logger = LogFactory.getLog(HbaseSynchronizationManager.class);
    // 创建ThreadLocal 用来存放tableName与Hbase table之间的映射内容
private static final ThreadLocal<Map<String, HTableInterface>> resources = new NamedThreadLocal<Map<String, HTableInterface>>("Bound resources");

/**
* Checks whether any resource is bound for the given key.
* 检查指定的table name 判断与其对应的hbase table resource 是否存在
* @param key key to check
* @return whether or not a resource is bound for the given key
*/
public static boolean hasResource(Object key) {
Object value = doGetResource(key);
return (value != null);
}

/**
* Returns the resource (table) associated with the given key.
* 根据指定的table name  返回对应的hbase table 内容
* @param key association key
* @return associated resource (table)
*/
public static HTableInterface getResource(Object key) {
return doGetResource(key);
}

/**
* Actually checks the value of the resource that is bound for the given key.
* 根据table name  返回对应的hbase table 内容
*/
private static HTableInterface doGetResource(Object actualKey) {
Map<String, HTableInterface> tables = resources.get();
if (tables == null) {
return null;
}
return tables.get(actualKey);
}

/**
* Binds the given resource for the given key to the current thread.
* 将key对应的resources添加到map中，并绑定到当前线程
* @param key the key to bind the value to (usually the resource factory)
* @param value the value to bind (usually the active resource object)
* @throws IllegalStateException if there is already a value bound to the thread
* @see ResourceTransactionManager#getResourceFactory()
*/
public static void bindResource(String key, HTableInterface value) throws IllegalStateException {
Assert.notNull(value, "Value must not be null");
// 判断当前线程中是否包含映射内容
// 若是存在 直接添加新内容
// 若不存在 则先创建map 再将对应的东西 再将map绑定到当前的线程 添加具体内容
Map<String, HTableInterface> map = resources.get();
// set ThreadLocal Map if none found
if (map == null) {
map = new LinkedHashMap<String, HTableInterface>();
resources.set(map);
}
HTableInterface oldValue = map.put(key, value);
if (oldValue != null) {
throw new IllegalStateException("Already value [" + oldValue + "] for key [" + key
+ "] bound to thread [" + Thread.currentThread().getName() + "]");
}
if (logger.isTraceEnabled()) {
logger.trace("Bound value [" + value + "] for key [" + key + "] to thread ["
+ Thread.currentThread().getName() + "]");
}
}

/**
* Unbinds a resource for the given key from the current thread.
* @param key the key to unbind (usually the resource factory)
* @return the previously bound value (usually the active resource object)
* @throws IllegalStateException if there is no value bound to the thread
* @see ResourceTransactionManager#getResourceFactory()
*/
public static HTableInterface unbindResource(String key) throws IllegalStateException {
HTableInterface value = doUnbindResource(key);
if (value == null) {
throw new IllegalStateException("No value for key [" + key + "] bound to thread ["
+ Thread.currentThread().getName() + "]");
}
return value;
}

/**
* Unbinds a resource for the given key from the current thread.
*
* @param key the key to unbind (usually the resource factory)
* @return the previously bound value, or <code>null</code> if none bound
*/
public static Object unbindResourceIfPossible(Object key) {
return doUnbindResource(key);
}

/**
* Actually remove the value of the resource that is bound for the given key.
* 根据指定key（table name） 完成将指定的资源 移除当前线程
*/
private static HTableInterface doUnbindResource(Object actualKey) {
Map<String, HTableInterface> map = resources.get();
if (map == null) {
return null;
}
HTableInterface value = map.remove(actualKey);
// 在解除指定的table name所关联的资源后，防止对应的map不能为空  进行map判断
// Remove entire ThreadLocal if empty...
if (map.isEmpty()) {
resources.remove();
}

if (value != null && logger.isTraceEnabled()) {
logger.trace("Removed value [" + value + "] for key [" + actualKey + "] from thread ["
+ Thread.currentThread().getName() + "]");
}
return value;
}

/**
* Returns the bound tables (by name).
*
* @return names of bound tables
*
*/
public static Set<String> getTableNames() {
Map<String, HTableInterface> map = resources.get();
if (map != null && !map.isEmpty()) {
return Collections.unmodifiableSet(map.keySet());
}
return Collections.emptySet();
}
}