mapreduce运行报错

前提：

确保 hadoop/bin 目录下的文件是完整的，直接从 apache 下载的会缺少文件，可以自己编译或从 GitHub 上下载其他人编译好的文件

确保软件 32 位或 64 位，保持一致

报出错误：

Exception in thread "main" java.lang.UnsatisfiedLinkError: org/apache/hadoop/io/nativeio/NativeIO$Windows.access0(Ljava/lang/String;I)Z
    at org.apache.hadoop.io.nativeio.NativeIO$Windows.access(NativeIO.java:640)
    at org.apache.hadoop.fs.FileUtil.canRead(FileUtil.java:1223)
    at org.apache.hadoop.fs.FileUtil.list(FileUtil.java:1428)
    at org.apache.hadoop.fs.RawLocalFileSystem.listStatus(RawLocalFileSystem.java:468)
    at org.apache.hadoop.fs.FileSystem.listStatus(FileSystem.java:1868)
    at org.apache.hadoop.fs.FileSystem.listStatus(FileSystem.java:1910)
    at org.apache.hadoop.fs.FileSystem$4.<init>(FileSystem.java:2072)
    at org.apache.hadoop.fs.FileSystem.listLocatedStatus(FileSystem.java:2071)
    at org.apache.hadoop.fs.ChecksumFileSystem.listLocatedStatus(ChecksumFileSystem.java:693)
    at org.apache.hadoop.mapreduce.lib.input.FileInputFormat.singleThreadedListStatus(FileInputFormat.java:312)
    at org.apache.hadoop.mapreduce.lib.input.FileInputFormat.listStatus(FileInputFormat.java:274)
    at org.apache.hadoop.mapreduce.lib.input.FileInputFormat.getSplits(FileInputFormat.java:396)
    at org.apache.hadoop.mapreduce.JobSubmitter.writeNewSplits(JobSubmitter.java:310)
    at org.apache.hadoop.mapreduce.JobSubmitter.writeSplits(JobSubmitter.java:327)
    at org.apache.hadoop.mapreduce.JobSubmitter.submitJobInternal(JobSubmitter.java:200)
    at org.apache.hadoop.mapreduce.Job$11.run(Job.java:1570)
    at org.apache.hadoop.mapreduce.Job$11.run(Job.java:1567)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:774)
    at java.base/javax.security.auth.Subject.doAs(Subject.java:427)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1729)
    at org.apache.hadoop.mapreduce.Job.submit(Job.java:1567)
    at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:1588)
    at com.hadoop.mapreduce.wordcount.WordCountDriver.main(WordCountDriver.java:40)

解决方法：强制加载hadoop.dll

另外：https://www.cnblogs.com/jhxxb/p/10723369.html

报出错误：

Exception in thread "main" org.apache.hadoop.mapred.FileAlreadyExistsException: Output directory file:/D:/hadoop/output1 already exists
    at org.apache.hadoop.mapreduce.lib.output.FileOutputFormat.checkOutputSpecs(FileOutputFormat.java:164)
    at org.apache.hadoop.mapreduce.JobSubmitter.checkSpecs(JobSubmitter.java:277)
    at org.apache.hadoop.mapreduce.JobSubmitter.submitJobInternal(JobSubmitter.java:143)
    at org.apache.hadoop.mapreduce.Job$11.run(Job.java:1570)
    at org.apache.hadoop.mapreduce.Job$11.run(Job.java:1567)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:774)
    at java.base/javax.security.auth.Subject.doAs(Subject.java:427)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1729)
    at org.apache.hadoop.mapreduce.Job.submit(Job.java:1567)
    at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:1588)
    at com.hadoop.mapreduce.wordcount.WordCountDriver.main(WordCountDriver.java:40)