（三）storm-kafka源代码走读之怎样构建一个KafkaSpout

上一节介绍了config的相关信息，这一节说下，这些參数各自是什么。在zookeeper中的存放路径是如何的，之前QQ群里有非常多不知道该怎么传入正确的參数来new 一个kafkaSpout，其主要还是參数传递正确就可。

看SpoutConfig的构造函数

public SpoutConfig(BrokerHosts hosts, String topic, String zkRoot, String id) {
        super(hosts, topic);
        this.zkRoot = zkRoot;
        this.id = id;
    }

须要一个BrokerHosts，看代码：

public class ZkHosts implements BrokerHosts {
    private static final String DEFAULT_ZK_PATH = "/brokers";

    public String brokerZkStr = null;
    public String brokerZkPath = null; // e.g., /kafka/brokers
    public int refreshFreqSecs = 60;

    public ZkHosts(String brokerZkStr, String brokerZkPath) {
        this.brokerZkStr = brokerZkStr;
        this.brokerZkPath = brokerZkPath;
    }

    public ZkHosts(String brokerZkStr) {
        this(brokerZkStr, DEFAULT_ZK_PATH);
    }
}

须要brokerZKStr,这个事实上就是hosts列表，多个host以逗号隔开。由于zookeeper解析string时是以逗号分隔的。这里附上zookeeper的解析代码

public ZooKeeper(String connectString, int sessionTimeout, Watcher watcher,
            boolean canBeReadOnly)
        throws IOException
    {
        LOG.info("Initiating client connection, connectString=" + connectString
                + " sessionTimeout=" + sessionTimeout + " watcher=" + watcher);

        watchManager.defaultWatcher = watcher;

        ConnectStringParser connectStringParser = new ConnectStringParser(
                connectString);
        HostProvider hostProvider = new StaticHostProvider(
                connectStringParser.getServerAddresses());
        cnxn = new ClientCnxn(connectStringParser.getChrootPath(),
                hostProvider, sessionTimeout, this, watchManager,
                getClientCnxnSocket(), canBeReadOnly);
        cnxn.start();
    }

当中主要StringParser做解析的，看俺怎样解析的就知道了

public ConnectStringParser(String connectString) {
        // parse out chroot, if any
        int off = connectString.indexOf('/');
        if (off >= 0) {
            String chrootPath = connectString.substring(off);
            // ignore "/" chroot spec, same as null
            if (chrootPath.length() == 1) {
                this.chrootPath = null;
            } else {
                PathUtils.validatePath(chrootPath);
                this.chrootPath = chrootPath;
            }
            connectString = connectString.substring(0, off);
        } else {
            this.chrootPath = null;
        }

        String hostsList[] = connectString.split(",");
        for (String host : hostsList) {
            int port = DEFAULT_PORT;
            int pidx = host.lastIndexOf(':');
            if (pidx >= 0) {
                // otherwise : is at the end of the string, ignore
                if (pidx < host.length() - 1) {
                    port = Integer.parseInt(host.substring(pidx + 1));
                }
                host = host.substring(0, pidx);
            }
            serverAddresses.add(InetSocketAddress.createUnresolved(host, port));
        }
    }

好了，这里就讲到这了。

刚才说到brokerZKStr须要。另一个參数就是zkpath，这个能够自己定，也有个默认值 “/brokers”

SpoutConfig还有个zkroot，这个zkroot事实上就是Consumer端消费的信息存放地方，好了给个样例：

String topic = “test”;  //
        String zkRoot = “/kafkastorm”; //
        String spoutId = “id”; //读取的status会被存在，/kafkastorm/id以下，所以id相似consumer group
        
        BrokerHosts brokerHosts = new ZkHosts("10.1.110.24:2181,10.1.110.22:2181"); // 这里使用默认的/brokers

        SpoutConfig spoutConfig = new SpoutConfig(brokerHosts, topic, zkRoot, spoutId);
        spoutConfig.scheme = new SchemeAsMultiScheme(new StringScheme()); // 下一节介绍 scheme
        
        /*spoutConfig.zkServers = new ArrayList<String>(){{ // 仅仅有在local模式下须要记录读取状态时。才须要设置
            add("10.118.136.107");
        }};
        spoutConfig.zkPort = 2181;*/

spoutConfig.forceFromStart = true; 
spoutConfig.startOffsetTime = -1;//从最新的開始消费 
spoutConfig.metricsTimeBucketSizeInSecs = 6; 
builder.setSpout(SqlCollectorTopologyDef.KAFKA_SPOUT_NAME, new KafkaSpout(spoutConfig), 1);

By default, the offsets will be stored in the same Zookeeper cluster that Storm uses. You can override this via your spout config like this:

spoutConfig.zkServers = ImmutableList.of("otherserver.com");
spoutConfig.zkPort = 2191;

这里就成功建了一个KafkaSpout。假设项目执行成功的话，

能够到zk master上看下相关信息，

./bin/zkCli.sh -server 10.1.110.24:2181

而对于StaticHosts来说，看官方解释：

StaticHosts

This is an alternative implementation where broker -> partition information is static. In order to construct an instance of this class you need to first construct an instance of GlobalPartitionInformation.

    Broker brokerForPartition0 = new Broker("localhost");//localhost:9092
    Broker brokerForPartition1 = new Broker("localhost", 9092);//localhost:9092 but we specified the port explicitly
    Broker brokerForPartition2 = new Broker("localhost:9092");//localhost:9092 specified as one string.
    GlobalPartitionInformation partitionInfo = new GlobalPartitionInformation();
    partitionInfo.addPartition(0, brokerForPartition0);//mapping form partition 0 to brokerForPartition0
    partitionInfo.addPartition(1, brokerForPartition1);//mapping form partition 1 to brokerForPartition1
    partitionInfo.addPartition(2, brokerForPartition2);//mapping form partition 2 to brokerForPartition2
    StaticHosts hosts = new StaticHosts(partitionInfo);

个人觉得是须要开发者，自己知道partition与broker之间的相应关系，正确关联起来。而storm-kafka 0.9.0.1的版本号是。不须要指定，我仅仅须要传入zkServer list，partition总数，由kafkautil利用两个for（遍历全部broker和partition）循环，暂时生成Consumer去连接消费一下试试，假设有数据，那么就把partitionId和brokerHost关系存到Map中去。可想而知0.9.3-rc1为什么要改成这样了。

假设该broker没有该partition信息，后果会如何？？？笔者没有測试过，有測试过的请留言，说一下情况。

Reference

http://www.cnblogs.com/fxjwind/p/3808346.html