Java中的奇数方法调用,使用点运算符访问泛型列表
我遇到了一些高级java代码(对我来说:)高级)我需要帮助理解。
在类中有一个嵌套类,如下所示:
private final class CoverageCRUDaoCallable implements
Callable<List<ClientCoverageCRU>>
{
private final long oid;
private final long sourceContextId;
private CoverageCRUDaoCallable(long oid, long sourceContextId)
{
this.oid = oid;
this.sourceContextId = sourceContextId;
}
@Override
public List<ClientCoverageCRU> call() throws Exception
{
return coverageCRUDao.getCoverageCRUData(oid, sourceContextId);
}
}
稍后在外部类中,有一个正在创建的可调用类的实例。我不知道这是什么:
ConnectionHelper.<List<ClientCoverageCRU>> tryExecute(coverageCRUDaoCallable);
对我来说,它看起来不像java语法。你能详细说说这个神秘的语法中发生了什么吗?您可以在下面的代码摘录中看到它被使用。
CoverageCRUDaoCallable coverageCRUDaoCallable = new CoverageCRUDaoCallable(
dalClient.getOid(), sourceContextId);
// use Connection helper to make coverageCRUDao call.
List<ClientCoverageCRU> coverageCRUList = ConnectionHelper
.<List<ClientCoverageCRU>> tryExecute(coverageCRUDaoCallable);
EDITED 添加了 ConnectionHelper 类。
public class ConnectionHelper<T>
{
private static final Logger logger =
LoggerFactory.getLogger(ConnectionHelper.class);
private static final int CONNECTION_RETRIES = 3;
private static final int MIN_TIMEOUT = 100;
public static <T> T tryExecute(Callable<T> command)
{
T returnValue = null;
long delay = 0;
for (int retry = 0; retry < CONNECTION_RETRIES; retry++)
{
try
{
// Sleep before retry
Thread.sleep(delay);
if (retry != 0)
{
logger.info("Connection retry #"+ retry);
}
// make the actual connection call
returnValue = command.call();
break;
}
catch (Exception e)
{
Throwable cause = e.getCause();
if (retry == CONNECTION_RETRIES - 1)
{
logger.info("Connection retries have exhausted. Not trying "
+ "to connect any more.");
throw new RuntimeException(cause);
}
// Delay increased exponentially with every retry.
delay = (long) (MIN_TIMEOUT * Math.pow(2, retry));
String origCause = ExceptionUtils.getRootCauseMessage(e);
logger.info("Connection retry #" + (retry + 1)
+ " scheduled in " + delay + " msec due to "
+ origCause);
+ origCause);
}
}
return returnValue;
}