在部署云 HDFS(Cloud HDFS,CHDFS) 的 JAR 包之后,除了可以使用命令行、大数据组件等方式操作 CHDFS ,还可以通过 Java 代码来访问 CHDFS。本文指导您如何通过 Java 代码访问 CHDFS。
新建 maven 工程,并在 maven 的 pom.xml 中添加以下依赖项(请根据自己实际 hadoop 环境设置 hadoop-common 包的版本)。
<dependencies>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-common</artifactId>
<version>2.8.5</version>
<scope>provided</scope>
</dependency>
</dependencies>
参考如下操作 hadoop 的代码进行修改,其中的配置项及其说明可参见 挂载 CHDFS。
以下只列出部分常见的文件系统操作接口,其他接口请参考 Hadoop FileSystem 接口文档。
package com.qcloud.chdfs.demo;
import org.apache.commons.io.IOUtils;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileChecksum;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import java.io.IOException;
import java.net.URI;
import java.nio.ByteBuffer;
public class Demo {
private static FileSystem initFS() throws IOException {
Configuration conf = new Configuration();
// CHDFS 的配置项可参见 https://www.tencentcloud.com/document/product/1105/36368?from_cn_redirect=1
// 以下配置是必填项
conf.set("fs.ofs.impl", "com.qcloud.chdfs.fs.CHDFSHadoopFileSystemAdapter");
conf.set("fs.AbstractFileSystem.ofs.impl", "com.qcloud.chdfs.fs.CHDFSDelegateFSAdapter");
conf.set("fs.ofs.tmp.cache.dir", "/data/chdfs_tmp_cache");
conf.set("fs.ofs.user.appid", "1250000000");
// 其他可选配置项请参见 https://www.tencentcloud.com/document/product/1105/36368?from_cn_redirect=1
String chdfsUrl = "ofs://f4maaabbb-ccdd.chdfs.ap-guangzhou.myqcloud.com/";
return FileSystem.get(URI.create(chdfsUrl), conf);
}
private static void mkdir(FileSystem fs, Path filePath) throws IOException {
fs.mkdirs(filePath);
}
private static void createFile(FileSystem fs, Path filePath) throws IOException {
// 创建一个文件(如果存在则将其覆盖)
// if the parent dir does not exist, fs will create it!
FSDataOutputStream out = fs.create(filePath, true);
try {
// 写入一个文件
String content = "test write file";
out.write(content.getBytes());
} finally {
IOUtils.closeQuietly(out);
}
}
private static void readFile(FileSystem fs, Path filePath) throws IOException {
FSDataInputStream in = fs.open(filePath);
try {
byte[] buf = new byte[4096];
int readLen = -1;
do {
readLen = in.read(buf);
} while (readLen >= 0);
} finally {
IOUtils.closeQuietly(in);
}
}
private static void queryFileOrDirStatus(FileSystem fs, Path path) throws IOException {
FileStatus fileStatus = fs.getFileStatus(path);
if (fileStatus.isDirectory()) {
System.out.printf("path %s is dir\n", path);
return;
}
long fileLen = fileStatus.getLen();
long accessTime = fileStatus.getAccessTime();
long modifyTime = fileStatus.getModificationTime();
String owner = fileStatus.getOwner();
String group = fileStatus.getGroup();
System.out.printf("path %s is file, fileLen: %d, accessTime: %d, modifyTime: %d, owner: %s, group: %s\n",
path, fileLen, accessTime, modifyTime, owner, group);
}
// 默认的校验类型为 COMPOSITE-CRC32C
private static void getFileCheckSum(FileSystem fs, Path path) throws IOException {
FileChecksum checksum = fs.getFileChecksum(path);
System.out.printf("path %s, checkSumType: %s, checkSumCrcVal: %d\n",
path, checksum.getAlgorithmName(), ByteBuffer.wrap(checksum.getBytes()).getInt());
}
private static void copyFileFromLocal(FileSystem fs, Path chdfsPath, Path localPath) throws IOException {
fs.copyFromLocalFile(localPath, chdfsPath);
}
private static void copyFileToLocal(FileSystem fs, Path chdfsPath, Path localPath) throws IOException {
fs.copyToLocalFile(chdfsPath, localPath);
}
private static void renamePath(FileSystem fs, Path oldPath, Path newPath) throws IOException {
fs.rename(oldPath, newPath);
}
private static void listDirPath(FileSystem fs, Path dirPath) throws IOException {
FileStatus[] dirMemberArray = fs.listStatus(dirPath);
for (FileStatus dirMember : dirMemberArray) {
System.out.printf("dirMember path %s, fileLen: %d\n", dirMember.getPath(), dirMember.getLen());
}
}
// 递归删除标志用于删除目录
// 如果递归为 false 并且 dir 不为空,则操作将失败
private static void deleteFileOrDir(FileSystem fs, Path path, boolean recursive) throws IOException {
fs.delete(path, recursive);
}
private static void closeFileSystem(FileSystem fs) throws IOException {
fs.close();
}
public static void main(String[] args) throws IOException {
// 初始化文件
FileSystem fs = initFS();
// 创建文件
Path chdfsFilePath = new Path("/folder/exampleobject.txt");
createFile(fs, chdfsFilePath);
// 读取文件
readFile(fs, chdfsFilePath);
// 查询文件或目录
queryFileOrDirStatus(fs, chdfsFilePath);
// 获取文件校验和
getFileCheckSum(fs, chdfsFilePath);
// 从本地复制文件
Path localFilePath = new Path("file:///home/hadoop/ofs_demo/data/exampleobject.txt");
copyFileFromLocal(fs, chdfsFilePath, localFilePath);
// 获取文件到本地
Path localDownFilePath = new Path("file:///home/hadoop/ofs_demo/data/exampleobject.txt");
copyFileToLocal(fs, chdfsFilePath, localDownFilePath);
// 重命名
Path newPath = new Path("/doc/example.txt");
renamePath(fs, chdfsFilePath, newPath);
// 删除文件
deleteFileOrDir(fs, newPath, false);
// 创建目录
Path dirPath = new Path("/folder");
mkdir(fs, dirPath);
// 在目录中创建文件
Path subFilePath = new Path("/folder/exampleobject.txt");
createFile(fs, subFilePath);
// 列出目录
listDirPath(fs, dirPath);
// 删除目录
deleteFileOrDir(fs, dirPath, true);
// 关闭文件系统
closeFileSystem(fs);
}
}
编译和运行。
说明:
- 运行前,请确保已正确设置 classpath。classpath 需包含 Hadoop common 包以及 CHDFS 包的路径。
- 对于 EMR 环境,如果您按照 挂载 CHDFS 逐步操作,那么 Hadoop common 包通常在
/usr/local/service/hadoop/share/hadoop/common/
目录下,CHDFS 包通常在/usr/local/service/hadoop/share/hadoop/common/lib/
目录下。
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