如何在Hadoop中自定义Writable类？

我正在尝试实现Writable类，但是如果在我的类中有嵌套对象，例如list等，我不知道如何实现可写类。任何正文可以帮助我吗？ 谢谢

public class StorageClass implements Writable{ public String xStr; public String yStr; public List sStor //omitted ctors @override public void write(DataOutput out) throws IOException{ out.writeChars(xStr); out.WriteChars(yStr); //WHAT SHOULD I DO FOR List } @override public void readFields(DataInput in) throws IOException{ xStr = in.readLine(); yStr = in.readLine(); //WHAT SHOULD I DO FOR List } } public class SubStorage{ public String x; public String y; } } 

以下是Field类：

 public final class Field implements Comparable, Serializable { private String name; private DataType dataType; private Object value; private FieldType fieldType; public Field(){ } public Field(String name, DataType dataType, FieldType fieldType){ this(name, dataType, null, fieldType); } public Field(String name, DataType type, Object value, FieldType fieldType){ this.name = name; this.dataType = type; this.value = value; this.fieldType = fieldType; } } public enum FieldType { PRI, LOOKUP, SCD, VERSION, OTHER } public enum DataType { UNDEFINED(4) { public int getSizeInBytes(Object value) { return STRING.getSizeInBytes(value); } }, STRING(4) { public int getSizeInBytes(Object value) { if (value == null) { return 0; } return super.getSizeInBytes(value) + (value.toString().length() * 2); // length + chars } }, INT(4), LONG(8), DOUBLE(8), DATETIME(8), BOOLEAN(1), BYTE(1), FLOAT(4), SHORT(2), CHAR(2), DATE(8), TIME(8), BLOB(0) { public int getSizeInBytes(Object value) { if (value == null) { return 0; } return ((byte[])value).length; } }; private final int sizeInBytes; private DataType(int sizeInBytes) { this.sizeInBytes = sizeInBytes; } public int getSizeInBytes(Object value) { return sizeInBytes; } } 

Answer 1

序列化集合非常简单。

 @Override public void readFields(DataInput in) throws IOException { int size = in.readInt(); list= new ArrayList(size); for(int i = 0; i < size; i++){ Field f = new Field(); f.readFields(in); list.add(f); } } @Override public void write(DataOutput out) throws IOException { out.writeInt(list.size()); for (Field l : list) { l.write(out); } } 

Field也必须实现Writable 。

Answer 2

本教程更好地解释： http ： //www.hadoopmaterial.com/2013/10/custom-hadoop-writable-data-type.html