问题
I keep getting an error which says 'cannot find symbol' while compiling WordCount.java. I tried importing the other libraries, but it only adds up to the list of errors. Am I missing some component that needs to be added?
javac -classpath /Documents/hadoop/hadoop-1.2.1/hadoop-core-1.2.1.jar:/Documents/hadoop/hadoop-1.2.1/lib/commons-cli-1.2.jar -d wordcount_classes WordCount.java
WordCount.java:4: error: package org.apache.hadoop.fs does not exist
import org.apache.hadoop.fs.Path;
^
WordCount.java:5: error: package org.apache.hadoop.io does not exist
import org.apache.hadoop.io.*;
^
WordCount.java:6: error: package org.apache.hadoop.mapred does not exist
import org.apache.hadoop.mapred.*;
^
WordCount.java:8: error: package org.apache.hadoop.mapred.lib.input does not exist
import org.apache.hadoop.mapred.lib.input.FileInputFormat;
^
WordCount.java:9: error: package org.apache.hadoop.mapred.lib.output does not exist
import org.apache.hadoop.mapred.lib.output.FileOutputFormat;
^
WordCount.java:10: error: package org.apache.hadoop.mapred.lib.input does not exist
import org.apache.hadoop.mapred.lib.input.TextInputFormat;
^
WordCount.java:15: error: cannot find symbol
public static class Map extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {
^
symbol: class MapReduceBase
location: class WordCount
WordCount.java:15: error: cannot find symbol
public static class Map extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {
^
symbol: class Mapper
location: class WordCount
WordCount.java:15: error: cannot find symbol
public static class Map extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {
^
symbol: class LongWritable
location: class WordCount
WordCount.java:15: error: cannot find symbol
public static class Map extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {
^
symbol: class Text
location: class WordCount
WordCount.java:15: error: cannot find symbol
public static class Map extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {
^
symbol: class Text
location: class WordCount
WordCount.java:15: error: cannot find symbol
public static class Map extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {
^
symbol: class IntWritable
location: class WordCount
WordCount.java:16: error: cannot find symbol
private final static IntWritable one = new IntWritable(1);
^
symbol: class IntWritable
location: class Map
WordCount.java:17: error: cannot find symbol
private Text word = new Text();
^
symbol: class Text
location: class Map
WordCount.java:19: error: cannot find symbol
public void map(LongWritable key, Text value, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
^
symbol: class LongWritable
location: class Map
WordCount.java:19: error: cannot find symbol
public void map(LongWritable key, Text value, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
^
symbol: class Text
location: class Map
WordCount.java:19: error: cannot find symbol
public void map(LongWritable key, Text value, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
^
symbol: class OutputCollector
location: class Map
WordCount.java:19: error: cannot find symbol
public void map(LongWritable key, Text value, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
^
symbol: class Text
location: class Map
WordCount.java:19: error: cannot find symbol
public void map(LongWritable key, Text value, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
^
symbol: class IntWritable
location: class Map
WordCount.java:19: error: cannot find symbol
public void map(LongWritable key, Text value, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
^
symbol: class Reporter
location: class Map
WordCount.java:28: error: cannot find symbol
public static class Reduce extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {
^
symbol: class MapReduceBase
location: class WordCount
WordCount.java:28: error: cannot find symbol
public static class Reduce extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {
^
symbol: class Reducer
location: class WordCount
WordCount.java:28: error: cannot find symbol
public static class Reduce extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {
^
symbol: class Text
location: class WordCount
WordCount.java:28: error: cannot find symbol
public static class Reduce extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {
^
symbol: class IntWritable
location: class WordCount
WordCount.java:28: error: cannot find symbol
public static class Reduce extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {
^
symbol: class Text
location: class WordCount
WordCount.java:28: error: cannot find symbol
public static class Reduce extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {
^
symbol: class IntWritable
location: class WordCount
WordCount.java:29: error: cannot find symbol
public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
^
symbol: class Text
location: class Reduce
WordCount.java:29: error: cannot find symbol
public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
^
symbol: class IntWritable
location: class Reduce
WordCount.java:29: error: cannot find symbol
public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
^
symbol: class OutputCollector
location: class Reduce
WordCount.java:29: error: cannot find symbol
public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
^
symbol: class Text
location: class Reduce
WordCount.java:29: error: cannot find symbol
public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
^
symbol: class IntWritable
location: class Reduce
WordCount.java:29: error: cannot find symbol
public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
^
symbol: class Reporter
location: class Reduce
WordCount.java:16: error: cannot find symbol
private final static IntWritable one = new IntWritable(1);
^
symbol: class IntWritable
location: class Map
WordCount.java:17: error: cannot find symbol
private Text word = new Text();
^
symbol: class Text
location: class Map
WordCount.java:34: error: cannot find symbol
output.collect(key, new IntWritable(sum));
^
symbol: class IntWritable
location: class Reduce
WordCount.java:39: error: cannot find symbol
JobConf conf = new JobConf(WordCount.class);
^
symbol: class JobConf
location: class WordCount
WordCount.java:39: error: cannot find symbol
JobConf conf = new JobConf(WordCount.class);
^
symbol: class JobConf
location: class WordCount
WordCount.java:42: error: cannot find symbol
conf.setOutputKeyClass(Text.class);
^
symbol: class Text
location: class WordCount
WordCount.java:43: error: cannot find symbol
conf.setOutputValueClass(IntWritable.class);
^
symbol: class IntWritable
location: class WordCount
WordCount.java:49: error: cannot find symbol
conf.setInputFormat(TextInputFormat.class);
^
symbol: class TextInputFormat
location: class WordCount
WordCount.java:50: error: cannot find symbol
conf.setOutputFormat(TextOutputFormat.class);
^
symbol: class TextOutputFormat
location: class WordCount
WordCount.java:52: error: cannot find symbol
FileInputFormat.setInputPaths(conf, new Path(args[0]));
^
symbol: class Path
location: class WordCount
WordCount.java:52: error: cannot find symbol
FileInputFormat.setInputPaths(conf, new Path(args[0]));
^
symbol: variable FileInputFormat
location: class WordCount
WordCount.java:53: error: cannot find symbol
FileOutputFormat.setOutputPath(conf, new Path(args[1]));
^
symbol: class Path
location: class WordCount
WordCount.java:53: error: cannot find symbol
FileOutputFormat.setOutputPath(conf, new Path(args[1]));
^
symbol: variable FileOutputFormat
location: class WordCount
WordCount.java:55: error: cannot find symbol
JobClient.runJob(conf);
^
symbol: variable JobClient
location: class WordCount
46 errors
回答1:
You can try this one:
javac -classpath hadoop-core-1.2.1.jar:lib/commons-cli-1.2.jar -d [path where u want to put the result] [path]/WordCount.java
回答2:
It seems your classpath doesn't include all required libs and jars.
For hadoop 2.7 you can easily run:
$hadoop classpath
This will return the full list of libs and jars which you need to include in your classpath.
or simpler you can just use the above command when you are compiling your code
$ javac -classpath $(hadoop classpath) -d wordcount_classes WordCount.java
回答3:
It is because the necessary packages are not included in javac classpath.
For hadoop 2.7.3, adding 3 packages works for me:
javac -classpath $HADOOP_HOME$/share/hadoop/common/hadoop-common-2.7.3.jar:$HADOOP_HOME$/share/hadoop/mapreduce/hadoop-mapreduce-client-core-2.7.3.jar:$HADOOP_HOME$/share/hadoop/common/lib/commons-cli-1.2.jar
-d wordcount_classes WordCount.java
回答4:
Some of the other answers cut to the chase and give pragmatic, quick solutions - which will work - but the official Hadoop Wordcount tutorial recommends that you call javac from bin/hadoop. This way, Hadoop will take care of the classpath conflicts for its own libraries.
The above-mentioned tutorial could however mislead you to point HADOOP_CLASSPATH to the wrong lib directory (there are distinct ones for the JDK and the JRE) thus missing tools.jar.*
My solution is to proceed as follow:
$ export HADOOP_PREFIX="${absolute/path/to/your/hadoop/binaries}"
$ export JDK_HOME="${absolute/path/to/your/jdk}"
$ export JAVA_HOME="${JDK_HOME}/jre"
$ export PATH="${JAVA_HOME}/bin:${PATH}"
$ export HADOOP_CLASSPATH="${JDK_HOME}/lib/tools.jar"
$ cd $HADOOP_PREFIX
$ bin/hadoop com.sun.tools.javac.Main ./path/to/WordCount.java
Note that the actual values to assign to JAVA_HOME and HADOOP_PREFIX must point to the locations where those tools are actually installed on your machine.
* it would cause Error: Could not find or load main class com.sun.tools.javac.Main at compile-time
来源：https://stackoverflow.com/questions/22600927/compilation-errors-while-compiling-wordcount-java