利用HDFS java API增删改查操作
利用HDFS java API增删改查操作
利用HDFS java API增删改查操作
在做这个实验的时候需要特别注意下面三个问题：
1、hdfs安全模式需要关闭命令：./hadoop dfsadmin -safemode leave
2、工程中依赖的版本必须和集群的一致，否则也会报 version不一致错误
3、hadoop集群用户权限的问题，以及各个目录的作用
目前为什么会有这三个问题的原因待查！！！
未验证目前使用hadoop的版本（release-0.20.0）是否支持webhdfs，反正我是怎么都连接不上啊！！！
从这上面看，0.20.0 可能是不支持的
https://jira.springsource.org/browse/IMPALA-15?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
Serengeti Distro:
Apache Hadoop:1.0.1
GreenPlum HD:1.1(Apache Hadoop 1.0.0)
CloudEra: CDH3(Apache Hadoop 0.20.2, WebHDFS is not supported in this version)
Hortonworks: 1.0.7 (Apache Hadoop 1.0.2)
步骤如下：
工程结构,如图：
工程结构
上代码 O(∩_∩)O哈哈~
pom.xml配置如下：
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd">
4.0.0
com.yun.hdfs
hdfs
0.0.1-SNAPSHOT
UTF-8
maven-assembly-plugin
false
jar-with-dependencies
com.yun.hdfs.WangPan
make-assembly
package
assembly
org.apache.hadoop
hadoop-core
0.20.2
jar
compile
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WangPan.java 主方法用于调用：
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package com.yun.hdfs;
import java.io.IOException;
public class WangPan {
private static String result =
"";
public static void main(String[] args) {
try {
// 判断命令输入是否正确
if (args[0] != null && !"".equals(args[0]) && args.length > 0) {
if ("upload".equals(args[0])) {
result = "upload:" + WangPanUtils.uploadFile(args);
} else if ("delete".equals(args[0])) {
result = "delete:" + WangPanUtils.deleteFile(args);
} else if ("query".equals(args[0])) {
if (WangPanUtils.listFile(args) == null) {
result = "query:fail!";
} else {
result = "query:success";
}
} else if ("read".equals(args[0])) {
result = "read:" + WangPanUtils.readFile(args);
} else {
System.out.println("sorry,wo have no this service!");
}
System.out.println(result);
} else {
System.out.println("fail!");
System.exit(1);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
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WangPanUtils.java增删改查：
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package com.yun.hdfs;
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URI;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FileUtil;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
public class WangPanUtils {
public static String uploadFile(String[] args) throws IOException {
String loaclSrc = args[1];
String dst = args[2];
if (args.length < 3) {
return "fail";
}
InputStream in = new BufferedInputStream(new
FileInputStream(loaclSrc));
Configuration conf = new Configuration();
FileSystem fs = FileSystem.get(URI.create(dst), conf);
OutputStream out = fs.create(new Path(dst));
IOUtils.copyBytes(in, out, 4096, true);
return "success";
}
public static Path[] listFile(String[] args) throws IOException {
if (args.length < 2) {
return null;
}
String dst = args[1];
Configuration conf = new Configuration();
FileSystem fs = FileSystem.get(URI.create(dst), conf);
FileStatus[] statu = fs.listStatus(new Path(dst));
Path[] listPaths = FileUtil.stat2Paths(statu);
return listPaths;
}
public static String deleteFile(String[] args) throws IOException {
if (args.length < 2) {
return "fail";
}
String fileName = args[1];
Configuration config = new Configuration();
FileSystem hdfs = FileSystem.get(URI.create(fileName), config);
Path path = new Path(fileName);
if (!hdfs.exists(path)) {
return "fail";
}
boolean isDeleted = hdfs.delete(path, false);
if (isDeleted) {
return "success";
} else {
return "fail";
}
}
public static String readFile(String[] args) throws IOException {
if(args.length < 3){
return "fail";
}
String dst = args[1];
String newPath = args[2];
Configuration conf = new Configuration();
FileSystem fs = FileSystem.get(URI.create(dst), conf);
FSDataInputStream hdfsInStream = fs.open(new
Path(dst));
OutputStream out = new FileOutputStream(newPath);
byte[] ioBuffer = new byte[1024];
int readLen = hdfsInStream.read(ioBuffer);
while (-1 != readLen) {
out.write(ioBuffer, 0, readLen);
readLen = hdfsInStream.read(ioBuffer);
}
out.close();
hdfsInStream.close();
fs.close();
return "success";
}
}
public static String mkdir(String[] args) throws IOException{
if(args.length < 2){
return "fali";
}
String dst = args[1];
Configuration conf = new Configuration();
FileSystem fs = FileSystem.get(URI.create(dst), conf);
Path path = new Path(dst);
if (fs.exists(path)) {
return "fail";
}
fs.mkdirs(path);
return "success";
}
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PS：需要注意的是，我们需要把这个工程利用maven打包成一个可运行的jar包，使用如下命令：
打包命令
执行命令在每个方法注释上写明了，执行效果如下：
增删改查效果
还需要访问 http://hadoopm:50070/ -> Browse the filesystem 查看hdfs文件操作是否真的成功
web hdfs
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