fastdfs 高并发场景下的异常处理

我们用fastdfs做为商户文件资料的存储，近期随着业务变动，也开始对外提供文件访问服务，发现请求偶尔会报错，异常大概如下：

java.net.SocketException: Connection reset
        at java.net.SocketInputStream.read(SocketInputStream.java:209) ~[na:1.8.0_74]
        at java.net.SocketInputStream.read(SocketInputStream.java:141) ~[na:1.8.0_74]
        at java.net.SocketInputStream.read(SocketInputStream.java:127) ~[na:1.8.0_74]
        at org.csource.fastdfs.ProtoCommon.recvHeader(ProtoCommon.java:168) ~[fastdfs-client-java-1.27.jar!/:na]
        at org.csource.fastdfs.ProtoCommon.recvPackage(ProtoCommon.java:201) ~[fastdfs-client-java-1.27.jar!/:na]
        at org.csource.fastdfs.TrackerClient.getStorages(TrackerClient.java:392) ~[fastdfs-client-java-1.27.jar!/:na]
        at org.csource.fastdfs.TrackerClient.getFetchStorage(TrackerClient.java:296) ~[fastdfs-client-java-1.27.jar!/:na]
        at org.csource.fastdfs.StorageClient.newReadableStorageConnection(StorageClient.java:1647) ~[fastdfs-client-java-1.27.jar!/:na]
        at org.csource.fastdfs.StorageClient.download_file(StorageClient.java:1118) ~[fastdfs-client-java-1.27.jar!/:na]
        at org.csource.fastdfs.StorageClient.download_file(StorageClient.java:1105) ~[fastdfs-client-java-1.27.jar!/:na]



java.io.IOException: recv package size -1 != 10
        at org.csource.fastdfs.ProtoCommon.recvHeader(ProtoCommon.java:169) ~[fastdfs-client-java-1.27.jar!/:na]
        at org.csource.fastdfs.ProtoCommon.recvPackage(ProtoCommon.java:201) ~[fastdfs-client-java-1.27.jar!/:na]
        at org.csource.fastdfs.TrackerClient.getStorages(TrackerClient.java:392) ~[fastdfs-client-java-1.27.jar!/:na]
        at org.csource.fastdfs.TrackerClient.getFetchStorage(TrackerClient.java:296) ~[fastdfs-client-java-1.27.jar!/:na]
        at org.csource.fastdfs.StorageClient.newReadableStorageConnection(StorageClient.java:1647) ~[fastdfs-client-java-1.27.jar!/:na]
        at org.csource.fastdfs.StorageClient.download_file(StorageClient.java:1118) ~[fastdfs-client-java-1.27.jar!/:na]
        at org.csource.fastdfs.StorageClient.download_file(StorageClient.java:1105) ~[fastdfs-client-java-1.27.jar!/:na]
        at com.ielpm.images.viewer.FastDFSClient.downloadFile(FastDFSClient.java:173) ~[classes!/:0.0.1-SNAPSHOT]
        at com.ielpm.images.viewer.ViewController.imgViewer(ViewController.java:53) ~[classes!/:0.0.1-SNAPSHOT]
        at sun.reflect.GeneratedMethodAccessor30.invoke(Unknown Source) ~[na:na]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_74]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_74]

软件环境如下：

• fastdfs：v5.05
• fastdfs_client_java：v1.27

解决方法：

1. 由于fastdfs客户端的实现中，storageClient、trackerServer和storageClient都不是线程安全的，而且，每次调用都会new一个socket连接，调用完成后会关闭，所以不能复用。

2. 在5.05版本中，storage和tracker的默认最大连接数（max_connections）为256，访问量一大就会超出报错，所以要根据场景，适当调整该值的大小。