java.io.IOException:Type mismatch in key from map:expected org.apache.hadoop.io.
?
job.setMapOutputKeyClass(IntWritable.class); job.setMapOutputValueClass(Text.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class);
if (key.getClass() != keyClass) {
??????? throw new IOException("Type mismatch in key from map: expected "
????????????????????????????? + keyClass.getName() + ", recieved "
????????????????????????????? + key.getClass().getName());
????? }
????? if (value.getClass() != valClass) {
??????? throw new IOException("Type mismatch in value from map: expected "
????????????????????????????? + valClass.getName() + ", recieved "
????????????????????????????? + value.getClass().getName());
????? }在MapOutputBuffer.collet()会检查实际传过来的Key Value 类型，和MapOutputBuffer初始化指定的KeyClass和ValueClass是否一样。?
keyClass = (Class<K>)job.getMapOutputKeyClass();
valClass = (Class<V>)job.getMapOutputValueClass();
public Class<?> getMapOutputKeyClass() {
??? Class<?> retv = getClass("mapred.mapoutput.key.class", null, Object.class);
??? if (retv == null) {
????? retv = getOutputKeyClass();
??? }
??? return retv;
? }public Class<?> getOutputKeyClass() {
??? return getClass("mapred.output.key.class",
??????????????????? LongWritable.class, Object.class); ?没用指定即采用默认的LongWritable
? }MapOutputBuffer.collet()
public synchronized void collect(K key, V value)??????? throws IOException {...}上述在程序中直接修改是一种方法，还有一种直接在命令行中指定key或者value类型
-D? mapred.mapoutput.key.class=org.apache.hadoop.io.LongWritable或者
-jobconf mapred.mapoutput.key.class=org.apache.hadoop.io.LongWritable