Develop Reference

Printing contents of an imported class to console in java

I'm programming in an online IDE (it is studio.code.org) (For a programming course). I would like to switch to a local IDE, but the online IDE uses some imports that are unavailable to download, but can be used in the code that has been written in the online IDE. This is in java. To make this a more general form of question that applies to (and will help) most people:
This is in java. I'm trying to print the contents of a file out in the console whose path is unknown, but is used as an import. Is it possible? If so, what code do I need to run to print the file out in console (from where I can copy paste it and use it elsewhere).
Here's the source code for something I tried to make this happen (but it didn't work, I'll show what output I got from the console below the code):
import java.io.*;
import org.code.neighborhood.Painter;
public class MyNeighborhood {
public static void main(String[] args) {
try {
Class<?> cls = Class.forName("org.code.neighborhood.Painter");
String fileName = cls.getName().replace('.', File.separatorChar) + ".class";
File file = new File(fileName);
System.out.println("File path: " + file.getAbsolutePath());
FileInputStream fis = new FileInputStream(file);
byte[] buffer = new byte[(int) file.length()];
fis.read(buffer);
fis.close();
System.out.println(new String(buffer));
} catch (Exception e) {
e.printStackTrace();
}
}
}
Output from console:
[JAVALAB] Connecting...
[JAVALAB] Compiling...
[JAVALAB] Compilation successful.
[JAVALAB] Running...
File path: /tmp/org/code/neighborhood/Painter.class
As you may have noticed I have found a file, but it is empty, although I know that the real file that is being imported is certainly not empty.
I do have read access to the system as well since I am able to navigate the root folder by using the code below:
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
public class Main {
public static void main(String[] args) {
boolean readContent = false; // change this to true to read file content, false to read file names
File directory = new File("/");
if (readContent) {
String fileName = "";
readFileContent(directory, fileName);
} else {
String[] fileNames = readFileNames(directory);
if (fileNames == null) {
System.out.println("Directory not found.");
} else {
System.out.println("Files in the directory:");
for (String fileName : fileNames) {
File file = new File(directory, fileName);
if (file.isDirectory()) {
System.out.println("Directory: " + fileName);
} else if (file.isFile()) {
System.out.println("File: " + fileName);
}
}
}
}
}
private static void readFileContent(File directory, String fileName) {
File file = new File(directory, fileName);
if (file.isFile()) {
try (FileReader reader = new FileReader(file)) {
int c;
while ((c = reader.read()) != -1) {
System.out.print((char) c);
}
} catch (IOException e) {
System.out.println("Error reading file: " + e.getMessage());
}
} else {
System.out.println("File not found.");
}
}
private static String[] readFileNames(File directory) {
if (directory.isDirectory()) {
return directory.list();
}
return null;
}
}

How to run Hadoop HDFS command from java code

I'm new in Hadoop! How can I run some hdfs commands from Java code? I've been testing successfully mapreduce with java code and hdfs commands directly from cloudera vm's terminal but now I'd like to learn how to do it with java code.
I've been looking for any materials where to learn but I haven't found yet.
Thanks

I think this may be help to you
I use it execute shell command well .here is the java example
public class JavaRunShell {
public static void main(String[] args){
try {
String shpath=" your command";
Process ps = Runtime.getRuntime().exec(shpath);
ps.waitFor();
}
catch (Exception e) {
e.printStackTrace();
}
}
}

As mentioned by Jagrut, you can use FileSystem API in your java code to interact with hdfs command. Below is the sample code where i am trying to check if a particular directory exists in hdfs or not. If exists, then remove that hdfs directory.
Configuration conf = new Configuration();
Job job = new Job(conf,"HDFS Connect");
FileSystem fs = FileSystem.get(conf);
Path outputPath = new Path("/user/cloudera/hdfsPath");
if(fs.exists(outputPath))
fs.delete(outputPath);
You can also refer to given blogs for further reference -
https://dzone.com/articles/working-with-the-hadoop-file-system-api, https://hadoop.apache.org/docs/r2.8.2/api/org/apache/hadoop/fs/FileSystem.html
https://blog.knoldus.com/2017/04/16/working-with-hadoop-filesystem-api/

You can use the FileSystem API in your Java code to interact with HDFS.

You can use FileSystem API in java code to perform Hdfs commands.
https://hadoop.apache.org/docs/r2.8.2/api/org/apache/hadoop/fs/FileSystem.html
Please find the following sample code.
package com.hadoop.FilesystemClasses;
import java.io.IOException;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.log4j.Logger;
import com.hadoop.Constants.Constants;
public class HdfsFileSystemTasks {
public static Logger logger = Logger.getLogger(HdfsFileSystemTasks.class
.getName());
public FileSystem configureFilesystem(String coreSitePath,
String hdfsSitePath) {
FileSystem fileSystem = null;
try {
Configuration conf = new Configuration();
Path hdfsCoreSitePath = new Path(coreSitePath);
Path hdfsHDFSSitePath = new Path(hdfsSitePath);
conf.addResource(hdfsCoreSitePath);
conf.addResource(hdfsHDFSSitePath);
fileSystem = FileSystem.get(conf);
return fileSystem;
} catch (Exception ex) {
ex.printStackTrace();
return fileSystem;
}
}
public String writeToHDFS(FileSystem fileSystem, String sourcePath,
String destinationPath) {
try {
Path inputPath = new Path(sourcePath);
Path outputPath = new Path(destinationPath);
fileSystem.copyFromLocalFile(inputPath, outputPath);
return Constants.SUCCESS;
} catch (IOException ex) {
ex.printStackTrace();
return Constants.FAILURE;
}
}
public String readFileFromHdfs(FileSystem fileSystem, String hdfsStorePath,
String localSystemPath) {
try {
Path hdfsPath = new Path(hdfsStorePath);
Path localPath = new Path(localSystemPath);
fileSystem.copyToLocalFile(hdfsPath, localPath);
return Constants.SUCCESS;
} catch (IOException ex) {
ex.printStackTrace();
return Constants.FAILURE;
}
}
public String deleteHdfsDirectory(FileSystem fileSystem,
String hdfsStorePath) {
try {
Path hdfsPath = new Path(hdfsStorePath);
if (fileSystem.exists(hdfsPath)) {
fileSystem.delete(hdfsPath);
logger.info("Directory{} Deleted Successfully "
+ hdfsPath);
} else {
logger.info("Input Directory{} does not Exists " + hdfsPath);
}
return Constants.SUCCESS;
} catch (Exception ex) {
System.out
.println("Some exception occurred while reading file from hdfs");
ex.printStackTrace();
return Constants.FAILURE;
}
}
public String deleteLocalDirectory(FileSystem fileSystem,
String localStorePath) {
try {
Path localPath = new Path(localStorePath);
if (fileSystem.exists(localPath)) {
fileSystem.delete(localPath);
logger.info("Input Directory{} Deleted Successfully "
+ localPath);
} else {
logger.info("Input Directory{} does not Exists " + localPath);
}
return Constants.SUCCESS;
} catch (Exception ex) {
System.out
.println("Some exception occurred while reading file from hdfs");
ex.printStackTrace();
return Constants.FAILURE;
}
}
public void closeFileSystem(FileSystem fileSystem) {
try {
fileSystem.close();
} catch (Exception ex) {
ex.printStackTrace();
System.out.println("Unable to close Hadoop filesystem : " + ex);
}
}
}
package com.hadoop.FileSystemTasks;
import com.hadoop.Constants.HDFSParameters;
import com.hadoop.Constants.HdfsFilesConstants;
import com.hadoop.Constants.LocalFilesConstants;
import com.hadoop.FilesystemClasses.HdfsFileSystemTasks;
import org.apache.hadoop.fs.FileSystem;
import org.apache.log4j.Logger;
public class ExecuteFileSystemTasks {
public static Logger logger = Logger.getLogger(ExecuteFileSystemTasks.class
.getName());
public static void main(String[] args) {
HdfsFileSystemTasks hdfsFileSystemTasks = new HdfsFileSystemTasks();
FileSystem fileSystem = hdfsFileSystemTasks.configureFilesystem(
HDFSParameters.CORE_SITE_XML_PATH,
HDFSParameters.HDFS_SITE_XML_PATH);
logger.info("File System Object {} " + fileSystem);
String fileWriteStatus = hdfsFileSystemTasks.writeToHDFS(fileSystem,
LocalFilesConstants.SALES_DATA_LOCAL_PATH,
HdfsFilesConstants.HDFS_SOURCE_DATA_PATH);
logger.info("File Write Status{} " + fileWriteStatus);
String filereadStatus = hdfsFileSystemTasks.readFileFromHdfs(
fileSystem, HdfsFilesConstants.HDFS_DESTINATION_DATA_PATH
+ "/MR_Job_Res2/part-r-00000",
LocalFilesConstants.MR_RESULTS_LOCALL_PATH);
logger.info("File Read Status{} " + filereadStatus);
String deleteDirStatus = hdfsFileSystemTasks.deleteHdfsDirectory(
fileSystem, HdfsFilesConstants.HDFS_DESTINATION_DATA_PATH
+ "/MR_Job_Res2");
hdfsFileSystemTasks.closeFileSystem(fileSystem);
}
}

#HbnKing I tried running your code but I kept getting errors. This is the error i got
java.io.IOException: Cannot run program "your": CreateProcess error=2, The system cannot
find the file specified
at java.lang.ProcessBuilder.start(Unknown Source)
at java.lang.Runtime.exec(Unknown Source)
at java.lang.Runtime.exec(Unknown Source)
at java.lang.Runtime.exec(Unknowenter code heren Source)
at jrs.main(jrs.java:5)

Java - Can't find and load a CSV file

For some reason, although I have already downloaded the CSV files, my program is unable to read them. My code is below, and it checks if the CSV file exists. If it does not, it goes to the URL and downloads and reads the code. However, it always re-downloads the code although it is in the path folder.
private void loadData(String path, String url) throws IOException{
File f = new File(path);
System.out.println("looking for path " + path);
if(f.exists()) {
readSavedFile(path); //method to load data
}
else{
System.out.println("Need to download from internet");
downloadAndRead(url, path);
}
}
This code outputs
looking for path C:\Users\n_000\workspace\Program\GOOG.csv
Need to download from internet.
looking for path C:\Users\n_000\workspace\Program\CHK.csv
Need to download from internet.
The code that I'm using to create the path is this:
String save = "filename"; //in program use this is the name of the stock eg GOOG or CHK
Path currentRelativePath = Paths.get("");
String savedFolder = currentRelativePath.toAbsolutePath().toString() + "\\";
path = savedFolder+save+".csv";

Its working fine,i didn't see any issues,i am posting my tested code,hope it may be useful.
import java.io.File;
import java.io.IOException;
import java.nio.file.Path;
import java.nio.file.Paths;
public class Test {
public static void main(String ar[])
{
Test test=new Test();
}
public Test()
{
String save = "GOOG"; //in program use this is the name of the stock eg GOOG or CHK
Path currentRelativePath = Paths.get("");
String savedFolder = currentRelativePath.toAbsolutePath().toString() + "\\";
String path = savedFolder+save+".csv";
String url=null;
try
{
loadData(path,url);
} catch (IOException e)
{
e.printStackTrace();
}
}
private void loadData(String path, String url) throws IOException
{
File f = new File(path);
System.out.println("looking for path " + path);
if(f.exists()) {
readSavedFile(path); //method to load data
}
else{
System.out.println("Need to download from internet");
downloadAndRead(url, path);
}
}
public void readSavedFile(String path)
{
System.out.println("Reading file");
}
public void downloadAndRead(String url,String path)
{
System.out.println("Downloding file");
}
}

java file.exists doesn't find my file

I'm using Windows7. I've written this simple java code:
package filetest;
import java.io.File;
public class FileTest {
public static void main(String[] args) {
File myfile = new File("C://test//test.txt");
if (myfile.exists()) {
System.out.println("file exists");
} else {
System.out.println("file doesn't exist");
}
}
}
The file DOES exists in C:/test/test.txt, but the answer is that file doesn't exists.
Why?
EDITED:
I've changed the code and it still doesn't find the file, but now it creates the file. So I can write to that directory. And the created file is named "test"
package filetest;
import java.io.File;
import java.util.*;
public class FileTest {
public static void main(String[] args) {
File myfile = new File("C:\\test\\test.txt");
final Formatter newfile;
if (myfile.exists()) {
System.out.println("file exists");
} else {
System.out.println("file doesn't exist");
try {
newfile = new Formatter("C://test//test.txt");
System.out.println("file has been created");
} catch(Exception e) {
System.out.println("Error: " + e);
}
}
}
}

In windows path separator used is '\' for these you need to escape backslash.So your code will be something like:
public class FileTest {
public static void main(String[] args) {
File myfile = new File("C:\\test\\test.txt");
if (myfile.exists()) {
System.out.println("file exists");
} else {
System.out.println("file doesn't exist");
}
}
}

You don't need to double your slashes. You have to user wether "/" or "\\".
EDIT :
The weird thing is that I tried it out and both "/" and "\\" work fine for me. In fact, it works regardless of the number of "/" I use... for example "C:////test/////////test.txt" is okay. You have another problem, and I have no idea of what it could be.

I would recommend using isFile() instead of exists(). Its a better way of checking if the path points to a file rather than if a file exists or not. exists() may return true if your path points to a directory.

#SSorensen In your EDITED code, you added the backslash properly
# line 7
File myfile = new File("C:\\test\\test.txt");
but you forgot to update slashes with backslashes # line 14
newfile = new Formatter("C://test//test.txt");

Failed to move file to another directory using renameTo

import java.io.File;
import org.apache.commons.io.FilenameUtils;
public class Tester {
public static void main(String[] args) {
String rootPath = "F:\\Java\\Java_Project";
File fRoot = new File(rootPath);
File[] fsSub = fRoot.listFiles();
for (File file : fsSub) {
if(file.isDirectory()) continue;
String fileNewPath = FilenameUtils.removeExtension(file.getPath()) + "\\" + file.getName();
File fNew = new File(fileNewPath);
try {
file.renameTo(fNew);
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
I am trying to move the file to another directory,for instance,if the File path is
"C:\out.txt"
than I want to move to
"C:\out\out.txt"
If i try to print the original File and the new original information, the work well,But they just can not move successful.

I suggest to try Java 7 NIO2
Files.move(Path source, Path target, CopyOption... options)