hadoop自定义类型异常java.lang.RuntimeException: java.lang.NoSuchMethodException: twicesort.TwoKey.<init>()

深碍√TFBOYSˉ_ 2022-06-07 04:29 56阅读 0赞

java.lang.RuntimeException: java.lang.NoSuchMethodException: twicesort.TwoKey.<init>()
        at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:131)
        at org.apache.hadoop.io.WritableComparator.newKey(WritableComparator.java:144)
        at org.apache.hadoop.io.WritableComparator.<init>(WritableComparator.java:130)
        at org.apache.hadoop.io.WritableComparator.get(WritableComparator.java:65)
        at org.apache.hadoop.mapred.JobConf.getOutputKeyComparator(JobConf.java:887)
        at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.init(MapTask.java:1001)
        at org.apache.hadoop.mapred.MapTask.createSortingCollector(MapTask.java:401)
        at org.apache.hadoop.mapred.MapTask.access$100(MapTask.java:81)
        at org.apache.hadoop.mapred.MapTask$NewOutputCollector.<init>(MapTask.java:695)
        at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:767)

**重点在这里，java.lang.NoSuchMethodException: twicesort.TwoKey，他说没有这个方法，这个方法是TwoKey的无参构造方法**  
这个细节在hadoop权威指南上也有提到，就在序列化或者自定义类型那章，具体不记得了，我的理解是首先他反序列化的时候先要拿到一个无参的构造对象，然后再进行对象内值的填充。

让我们再来看看hadoop给我提供的类型是不是都有无参的构造方法

public class IntWritable implements WritableComparable<IntWritable> {
      private int value;
    
      public IntWritable() {}
    
      public IntWritable(int value) { set(value); }
      }

public class LongWritable implements WritableComparable<LongWritable> {
      private long value;
    
      public LongWritable() {}
    
      public LongWritable(long value) { set(value); }
      }

public class Text extends BinaryComparable
        implements WritableComparable<BinaryComparable> {
        public Text() {
        bytes = EMPTY_BYTES;
      }
    
      /** Construct from a string. */
      public Text(String string) {
        set(string);
      }
    
      /** Construct from another text. */
      public Text(Text utf8) {
        set(utf8);
      }
    
      /** Construct from a byte array. */
      public Text(byte[] utf8)  {
        set(utf8);
      }
      }

public class BooleanWritable implements WritableComparable<BooleanWritable> { 
      private boolean value;
    
      /** */
      public BooleanWritable() {};
      }

public class ByteWritable implements WritableComparable<ByteWritable> {
      private byte value;
    
      public ByteWritable() {}
    
      public ByteWritable(byte value) { set(value); }
      }

public class ShortWritable implements WritableComparable<ShortWritable> {
      private short value;
    
      public ShortWritable() {
      }
    
      public ShortWritable(short value) {
        set(value);
      }
    }