首先保证JDK、Hadoop安装设置成功
可以参考[linux]ubuntu下安装hadoop [linux]ubutnu12.04 下安装jdk1.7
使用hadoop版本为1.2.1，jdk为1.7
在hadoop-1.2.1\src\examples\org\apache\hadoop\examples找到WordCount.java
源码如下：
1 /**
2 * Licensed under the Apache License, Version 2.0 (the "License");
3 * you may not use this file except in compliance with the License.
4 * You may obtain a copy of the License at
5 *
6 * http://www.apache.org/licenses/LICENSE-2.0
7 *
8 * Unless required by applicable law or agreed to in writing, software
9 * distributed under the License is distributed on an "AS IS" BASIS,
10 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
11 * See the License for the specific language governing permissions and
12 * limitations under the License.
13 */
14
15
16 package org.apache.hadoop.examples;
17
18 import java.io.IOException;
19 import java.util.StringTokenizer;
20
21 import org.apache.hadoop.conf.Configuration;
22 import org.apache.hadoop.fs.Path;
23 import org.apache.hadoop.io.IntWritable;
24 import org.apache.hadoop.io.Text;
25 import org.apache.hadoop.mapreduce.Job;
26 import org.apache.hadoop.mapreduce.Mapper;
27 import org.apache.hadoop.mapreduce.Reducer;
28 import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
29 import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
30 import org.apache.hadoop.util.GenericOptionsParser;
31
32 public class WordCount {
33
34 public static class TokenizerMapper
35 extends Mapper<Object, Text, Text, IntWritable>{
36
37 private final static IntWritable one = new IntWritable(1);
38 private Text word = new Text();
39
40 public void map(Object key, Text value, Context context
41 ) throws IOException, InterruptedException {
42 StringTokenizer itr = new StringTokenizer(value.toString());
43 while (itr.hasMoreTokens()) {
44 word.set(itr.nextToken());
45 context.write(word, one);
46 }
47 }
48 }
49
50 public static class IntSumReducer
51 extends Reducer<Text,IntWritable,Text,IntWritable> {
52 private IntWritable result = new IntWritable();
53
54 public void reduce(Text key, Iterable<IntWritable> values,
55 Context context
56 ) throws IOException, InterruptedException {
57 int sum = 0;
58 for (IntWritable val : values) {
59 sum += val.get();
60 }
61 result.set(sum);
62 context.write(key, result);
63 }
64 }
65
66 public static void main(String[] args) throws Exception {
67 Configuration conf = new Configuration();
68 String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
69 if (otherArgs.length != 2) {
70 System.err.println("Usage: wordcount <in> <out>");
71 System.exit(2);
72 }
73 Job job = new Job(conf, "word count");
74 job.setJarByClass(WordCount.class);
75 job.setMapperClass(TokenizerMapper.class);
76 job.setCombinerClass(IntSumReducer.class);
77 job.setReducerClass(IntSumReducer.class);
78 job.setOutputKeyClass(Text.class);
79 job.setOutputValueClass(IntWritable.class);
80 FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
81 FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
82 System.exit(job.waitForCompletion(true) ? 0 : 1);
83 }
84 }
在hadoop主目录下新建classes用于存放编译后的.class文件
mkdir hadoop1.2.1/classes
把WordCount.java放入classes文件夹中
我们直接在classes编译一下WordCount.java
javac WordCount.java -d .
出现如下错误
1 WordCount.java:21: error: package org.apache.hadoop.conf does not exist
2 import org.apache.hadoop.conf.Configuration;
3 ^
4 WordCount.java:22: error: package org.apache.hadoop.fs does not exist
5 import org.apache.hadoop.fs.Path;
6 ^
7 WordCount.java:23: error: package org.apache.hadoop.io does not exist
8 import org.apache.hadoop.io.IntWritable;
9 ^
10 WordCount.java:24: error: package org.apache.hadoop.io does not exist
11 import org.apache.hadoop.io.Text;
12 ^
13 WordCount.java:25: error: package org.apache.hadoop.mapreduce does not exist
14 import org.apache.hadoop.mapreduce.Job;
15 ^
16 WordCount.java:26: error: package org.apache.hadoop.mapreduce does not exist
17 import org.apache.hadoop.mapreduce.Mapper;
18 ^
19 WordCount.java:27: error: package org.apache.hadoop.mapreduce does not exist
20 import org.apache.hadoop.mapreduce.Reducer;
21 ^
22 WordCount.java:28: error: package org.apache.hadoop.mapreduce.lib.input does not exist
23 import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
24 ^
25 WordCount.java:29: error: package org.apache.hadoop.mapreduce.lib.output does not exist
26 import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
27 ^
28 WordCount.java:30: error: package org.apache.hadoop.util does not exist
29 import org.apache.hadoop.util.GenericOptionsParser;
30 ^
31 WordCount.java:35: error: cannot find symbol
32 extends Mapper<Object, Text, Text, IntWritable>{
33 ^
34 symbol: class Mapper
35 location: class WordCount
36 WordCount.java:35: error: cannot find symbol
37 extends Mapper<Object, Text, Text, IntWritable>{
38 ^
39 symbol: class Text
40 location: class WordCount
41 WordCount.java:35: error: cannot find symbol
42 extends Mapper<Object, Text, Text, IntWritable>{
43 ^
44 symbol: class Text
45 location: class WordCount
46 WordCount.java:35: error: cannot find symbol
47 extends Mapper<Object, Text, Text, IntWritable>{
48 ^
49 symbol: class IntWritable
50 location: class WordCount
51 WordCount.java:37: error: cannot find symbol
52 private final static IntWritable one = new IntWritable(1);
53 ^
54 symbol: class IntWritable
55 location: class TokenizerMapper
56 WordCount.java:38: error: cannot find symbol
57 private Text word = new Text();
58 ^
59 symbol: class Text
60 location: class TokenizerMapper
61 WordCount.java:40: error: cannot find symbol
62 public void map(Object key, Text value, Context context
63 ^
64 symbol: class Text
65 location: class TokenizerMapper
66 WordCount.java:40: error: cannot find symbol
67 public void map(Object key, Text value, Context context
68 ^
69 symbol: class Context
70 location: class TokenizerMapper
71 WordCount.java:51: error: cannot find symbol
72 extends Reducer<Text,IntWritable,Text,IntWritable> {
73 ^
74 symbol: class Reducer
75 location: class WordCount
76 WordCount.java:51: error: cannot find symbol
77 extends Reducer<Text,IntWritable,Text,IntWritable> {
78 ^
79 symbol: class Text
80 location: class WordCount
81 WordCount.java:51: error: cannot find symbol
82 extends Reducer<Text,IntWritable,Text,IntWritable> {
83 ^
84 symbol: class IntWritable
85 location: class WordCount
86 WordCount.java:51: error: cannot find symbol
87 extends Reducer<Text,IntWritable,Text,IntWritable> {
88 ^
89 symbol: class Text
90 location: class WordCount
91 WordCount.java:51: error: cannot find symbol
92 extends Reducer<Text,IntWritable,Text,IntWritable> {
93 ^
94 symbol: class IntWritable
95 location: class WordCount
96 WordCount.java:52: error: cannot find symbol
97 private IntWritable result = new IntWritable();
98 ^
99 symbol: class IntWritable
100 location: class IntSumReducer
101 WordCount.java:54: error: cannot find symbol
102 public void reduce(Text key, Iterable<IntWritable> values,
103 ^
104 symbol: class Text
105 location: class IntSumReducer
106 WordCount.java:54: error: cannot find symbol
107 public void reduce(Text key, Iterable<IntWritable> values,
108 ^
109 symbol: class IntWritable
110 location: class IntSumReducer
111 WordCount.java:55: error: cannot find symbol
112 Context context
113 ^
114 symbol: class Context
115 location: class IntSumReducer
116 WordCount.java:37: error: cannot find symbol
117 private final static IntWritable one = new IntWritable(1);
118 ^
119 symbol: class IntWritable
120 location: class TokenizerMapper
121 WordCount.java:38: error: cannot find symbol
122 private Text word = new Text();
123 ^
124 symbol: class Text
125 location: class TokenizerMapper
126 WordCount.java:52: error: cannot find symbol
127 private IntWritable result = new IntWritable();
128 ^
129 symbol: class IntWritable
130 location: class IntSumReducer
131 WordCount.java:58: error: cannot find symbol
132 for (IntWritable val : values) {
133 ^
134 symbol: class IntWritable
135 location: class IntSumReducer
136 WordCount.java:67: error: cannot find symbol
137 Configuration conf = new Configuration();
138 ^
139 symbol: class Configuration
140 location: class WordCount
141 WordCount.java:67: error: cannot find symbol
142 Configuration conf = new Configuration();
143 ^
144 symbol: class Configuration
145 location: class WordCount
146 WordCount.java:68: error: cannot find symbol
147 String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
148 ^
149 symbol: class GenericOptionsParser
150 location: class WordCount
151 WordCount.java:73: error: cannot find symbol
152 Job job = new Job(conf, "word count");
153 ^
154 symbol: class Job
155 location: class WordCount
156 WordCount.java:73: error: cannot find symbol
157 Job job = new Job(conf, "word count");
158 ^
159 symbol: class Job
160 location: class WordCount
161 WordCount.java:78: error: cannot find symbol
162 job.setOutputKeyClass(Text.class);
163 ^
164 symbol: class Text
165 location: class WordCount
166 WordCount.java:79: error: cannot find symbol
167 job.setOutputValueClass(IntWritable.class);
168 ^
169 symbol: class IntWritable
170 location: class WordCount
171 WordCount.java:80: error: cannot find symbol
172 FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
173 ^
174 symbol: class Path
175 location: class WordCount
176 WordCount.java:80: error: cannot find symbol
177 FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
178 ^
179 symbol: variable FileInputFormat
180 location: class WordCount
181 WordCount.java:81: error: cannot find symbol
182 FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
183 ^
184 symbol: class Path
185 location: class WordCount
186 WordCount.java:81: error: cannot find symbol
187 FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
188 ^
189 symbol: variable FileOutputFormat
190 location: class WordCount
191 42 errors
原因是缺少依赖包
因为源码import了好几个hadoop自定义类，非JDK环境自带的类，所以需要把这些依赖包导入eclipse中，不然编译器如何能找到这些类呢，得明确让编译器知道这些类所在位置。
而hadoop的依赖包就是hadoop1.2.1下的几个jar文件，以及hadoop/lib下的jar文件。
有时候不知道源代码使用了哪一个依赖包，所以把全部依赖包告诉编译器，我使用的方法是在~/.bashrc设置一个hadoop_CLASSPATH变量（最好不用使用HADOOP_CLASSPATH变量名，因为在hadoop1.2.1/conf/hadoop-env.sh中有这个变量名，所以最好不要使用）
hadoop_CLASSPATH如下产生。
hadoop_HOME=/home/hadoop/hadoop1.2.1
#HADOOP_HOME不能占用，因为hadoop-env.sh中有使用
for f in $hadoop_HOME/hadoop-*.jar; do
hadoop_CLASSPATH=${hadoop_CLASSPATH}:$f
done
for f in $hadoop_HOME/lib/*.jar; do
hadoop_CLASSPATH=${hadoop_CLASSPATH}:$f
done
看一下javac命令的用法
1 Usage: javac <options> <source files>
2 where possible options include:
3 -g Generate all debugging info
4 -g:none Generate no debugging info
5 -g:{lines,vars,source} Generate only some debugging info
6 -nowarn Generate no warnings
7 -verbose Output messages about what the compiler is doing
8 -deprecation Output source locations where deprecated APIs are used
9 -classpath <path> Specify where to find user class files and annotation processors
10 -cp <path> Specify where to find user class files and annotation processors
11 -sourcepath <path> Specify where to find input source files
12 -bootclasspath <path> Override location of bootstrap class files
13 -extdirs <dirs> Override location of installed extensions
14 -endorseddirs <dirs> Override location of endorsed standards path
15 -proc:{none,only} Control whether annotation processing and/or compilation is done.
16 -processor <class1>[,<class2>,<class3>...] Names of the annotation processors to run; bypasses default discovery process
17 -processorpath <path> Specify where to find annotation processors
18 -d <directory> Specify where to place generated class files
19 -s <directory> Specify where to place generated source files
20 -implicit:{none,class} Specify whether or not to generate class files for implicitly referenced files
21 -encoding <encoding> Specify character encoding used by source files
22 -source <release> Provide source compatibility with specified release
23 -target <release> Generate class files for specific VM version
24 -version Version information
25 -help Print a synopsis of standard options
26 -Akey[=value] Options to pass to annotation processors
27 -X Print a synopsis of nonstandard options
28 -J<flag> Pass <flag> directly to the runtime system
29 -Werror Terminate compilation if warnings occur
30 @<filename> Read options and filenames from file
参数classpath与cp均是设置依赖包的途径
1 -classpath <path> Specify where to find user class files and annotation processors 2 -cp <path> Specify where to find user class files and annotation processors
可以如下编译
javac -cp $hadoop_CLASSPATH WordCount.java -d .
编译成功，classes文件夹出现了一个org的文件夹，点击进去可以发现文件夹的层次是org/apache/hadoop/examples 然后在examples文件夹中看到三个.class
[email protected] ~/hadoop-1.2.1/classes/org/apache/hadoop/examples $ pwd /home/hadoop/hadoop-1.2.1/classes/org/apache/hadoop/examples [email protected] ~/hadoop-1.2.1/classes/org/apache/hadoop/examples $ ls WordCount.class WordCount$IntSumReducer.class WordCount$TokenizerMapper.class
层次结构出现的原因是源代码开始是有一个package org.apache.hadoop.examples;
如果没有，三个c.lass直接出现在classes中。
然后返回classes目录，打包为jar文件
jar -cvf WordCount.jar org
然后当前文件夹就会出现WordCount.jar文件，可以使用jar -tvf WordCount.jar看一下这个包的层次结构
jar -tvf WordCount.jar 0 Fri Aug 15 19:58:32 CST 2014 META-INF/ 68 Fri Aug 15 19:58:32 CST 2014 META-INF/MANIFEST.MF 0 Fri Aug 15 19:53:28 CST 2014 org/ 0 Fri Aug 15 19:53:28 CST 2014 org/apache/ 0 Fri Aug 15 19:53:28 CST 2014 org/apache/hadoop/ 0 Fri Aug 15 19:53:28 CST 2014 org/apache/hadoop/examples/ 1911 Fri Aug 15 19:53:28 CST 2014 org/apache/hadoop/examples/WordCount.class 1790 Fri Aug 15 19:53:28 CST 2014 org/apache/hadoop/examples/WordCount$TokenizerMapper.class 1793 Fri Aug 15 19:53:28 CST 2014 org/apache/hadoop/examples/WordCount$IntSumReducer.class
WordCount.jar打包成功，运行WordCount详解可以参考Hadoop集群（第6期）_WordCount运行详解
hadoop jar WordCount.jar org.apache.hadoop.examples.WordCount input output
org.apache.hadoop.examples.WordCount是程序的主类WordCount.class名字，这里就不需要加.class后缀。如果没有层次结构的话，就直接是
hadoop jar WordCount.jar WordCount input output
WordCount.jar不一定是与主类相同，可以是CountWord.jar或者其他名字，但是上述命令hadoop jar 包名 程序主类名字 输入文件夹 输出文件夹
程序主类名字就一定不能换成其他，得是主类名字，不然不能运行。
[hadoop]命令行编译并运行hadoop例子WordCount,布布扣,bubuko.com
时间： 2024-08-02 06:57:57