org.apache.hadoop.fs-BlockLocation

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工具类吧

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 package org.apache.hadoop.fs;

 import org.apache.hadoop.io.*;
 //IO包下的类还没涉及到。遇到一个分析一个。
 import java.io.*;

 /*
  * A BlockLocation lists hosts, offset and length
  * of block.
  *
  */
 //记录block的元数据信息，如所在host，长度和偏移量
 public class BlockLocation implements Writable {
 //针对集群块位置的类
   static {               // register a ctor
     WritableFactories.setFactory
       (BlockLocation.class,
        new WritableFactory() {
          public Writable newInstance() { return new BlockLocation(); }
        });
   }
 //注册了一个Writable子类BlockLocation的工厂。内部类。详细可看http://book.2cto.com/201305/21915.html
   private String[] hosts; //hostnames of datanodes
   //节点的主机名数组
   private String[] names; //hostname:portNumber of datanodes
   //节点的名称数组。名称的格式。
   private String[] topologyPaths; // full path name in network topology
   //节点在网络拓扑结构中的地址
   private long offset;  //offset of the of the block in the file
   //块在文件中的偏移量
   private long length;
   //块长度

   /**
    * Default Constructor
    */
   public BlockLocation() {
     this(new String[0], new String[0],  0L, 0L);
   }
 //默认构造方法
   /**
    * Constructor with host, name, offset and length
    */
   public BlockLocation(String[] names, String[] hosts, long offset,
                        long length) {
     if (names == null) {
       this.names = new String[0];
     } else {
       this.names = names;
     }
     if (hosts == null) {
       this.hosts = new String[0];
     } else {
       this.hosts = hosts;
     }
     this.offset = offset;
     this.length = length;
     this.topologyPaths = new String[0];
   }
 //根据名称主机偏移量长度初始化一个块对象
   /**
    * Constructor with host, name, network topology, offset and length
    */
   public BlockLocation(String[] names, String[] hosts, String[] topologyPaths,
                        long offset, long length) {
     this(names, hosts, offset, length);
     if (topologyPaths == null) {
       this.topologyPaths = new String[0];
     } else {
       this.topologyPaths = topologyPaths;
     }
   }
 //根据.........
   /**
    * Get the list of hosts (hostname) hosting this block
    */
   public String[] getHosts() throws IOException {
     if ((hosts == null) || (hosts.length == 0)) {
       return new String[0];
     } else {
       return hosts;
     }
   }
 //获得块的主机
   /**
    * Get the list of names (hostname:port) hosting this block
    */
   public String[] getNames() throws IOException {
     if ((names == null) || (names.length == 0)) {
       return new String[0];
     } else {
       return this.names;
     }
   }
 //。。。。
   /**
    * Get the list of network topology paths for each of the hosts.
    * The last component of the path is the host.
    */
   public String[] getTopologyPaths() throws IOException {
     if ((topologyPaths == null) || (topologyPaths.length == 0)) {
       return new String[0];
     } else {
       return this.topologyPaths;
     }
   }
   //。。。。。
   /**
    * Get the start offset of file associated with this block
    */
   public long getOffset() {
     return offset;
   }
   //。。。。。
   /**
    * Get the length of the block
    */
   public long getLength() {
     return length;
   }
   //。。。。。
   /**
    * Set the start offset of file associated with this block
    */
   public void setOffset(long offset) {
     this.offset = offset;
   }
 //。。。。。
   /**
    * Set the length of block
    */
   public void setLength(long length) {
     this.length = length;
   }
 //。。。。。
   /**
    * Set the hosts hosting this block
    */
   public void setHosts(String[] hosts) throws IOException {
     if (hosts == null) {
       this.hosts = new String[0];
     } else {
       this.hosts = hosts;
     }
   }
 //。。。。。
   /**
    * Set the names (host:port) hosting this block
    */
   public void setNames(String[] names) throws IOException {
     if (names == null) {
       this.names = new String[0];
     } else {
       this.names = names;
     }
   }
 //。。。。。
   /**
    * Set the network topology paths of the hosts
    */
   public void setTopologyPaths(String[] topologyPaths) throws IOException {
     if (topologyPaths == null) {
       this.topologyPaths = new String[0];
     } else {
       this.topologyPaths = topologyPaths;
     }
   }
 //。。。。。
   /**
    * Implement write of Writable
    */
   public void write(DataOutput out) throws IOException {
     out.writeLong(offset);
     out.writeLong(length);
     out.writeInt(names.length);
     for (int i=0; i < names.length; i++) {
       Text name = new Text(names[i]);
       name.write(out);
     }
     out.writeInt(hosts.length);
     for (int i=0; i < hosts.length; i++) {
       Text host = new Text(hosts[i]);
       host.write(out);
     }
     out.writeInt(topologyPaths.length);
     for (int i=0; i < topologyPaths.length; i++) {
       Text host = new Text(topologyPaths[i]);
       host.write(out);
     }
   }
   //把块信息写到输出流中。用到了Writable子类Long,Int,Text的Write方法。序列化
   /**
    * Implement readFields of Writable
    */
   public void readFields(DataInput in) throws IOException {
     this.offset = in.readLong();
     this.length = in.readLong();
     int numNames = in.readInt();
     this.names = new String[numNames];
     for (int i = 0; i < numNames; i++) {
       Text name = new Text();
       name.readFields(in);
       names[i] = name.toString();
     }
     int numHosts = in.readInt();
     for (int i = 0; i < numHosts; i++) {
       Text host = new Text();
       host.readFields(in);
       hosts[i] = host.toString();
     }
     int numTops = in.readInt();
     Text path = new Text();
     for (int i = 0; i < numTops; i++) {
       path.readFields(in);
       topologyPaths[i] = path.toString();
     }
   }
   //把块信息从输入流中读出来。....。反序列化
   public String toString() {
     StringBuilder result = new StringBuilder();
     result.append(offset);
     result.append(',');
     result.append(length);
     for(String h: hosts) {
       result.append(',');
       result.append(h);
     }
     return result.toString();
   }
   //。。。。。。
 }