I have a file I'm using to hold system information that my program needs on execution.
The program will read from it and write to it periodically. How do I do this? Among other problems, I'm having trouble with paths
Example
How do I read/write to this properites file if deploying application as runnable jar
Take a look at the http://docs.oracle.com/javase/6/docs/api/java/util/Properties.html
You can utilize this class to use your key=value pairs in the property/config file
Second part of your question, how to build a runnable jar. I'd do that with maven, take a look at this :
How can I create an executable JAR with dependencies using Maven?
and this :
http://maven.apache.org/guides/getting-started/maven-in-five-minutes.html
I see you're not using maven to build your project altogether
You can't write to a file that exists as part of a ZIP file... it does not exist as a file on the filesystem.
Considered the Preferences API?
To read from a file you can declare a file reader using a scanner as
Scanner diskReader = new Scanner(new File("myProp.properties"));
After then for example if you want to read a boolean value from the properties file use
boolean Example = diskReader.nextBoolean();
If you wan't to write to a file it's a bit more complicated but this is how I do it:
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Random;
import java.util.Scanner;
public class UpdateAFile {
static Random random = new Random();
static int numberValue = random.nextInt(100);
public static void main(String[] args) {
File file = new File("myFile.txt");
BufferedWriter writer = null;
Scanner diskScanner = null;
try {
writer = new BufferedWriter(new FileWriter(file, true));
} catch (IOException e) {
e.printStackTrace();
}
try {
diskScanner = new Scanner(file);
} catch (FileNotFoundException e1) {
e1.printStackTrace();
}
appendTo(writer, Integer.valueOf(numberValue).toString());
int otherValue = diskScanner.nextInt();
appendTo(writer, Integer.valueOf(otherValue + 10).toString());
int yetAnotherValue = diskScanner.nextInt();
appendTo(writer, Integer.valueOf(yetAnotherValue * 10).toString());
try {
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}
static void appendTo(BufferedWriter writer, String string) {
try {
writer.write(string);
writer.newLine();
writer.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
}
And then write to the file by:
diskWriter.write("BlahBlahBlah");
Related
When I display the variable data using System.out.println(data), it displays the content (all lines) of the "filename.txt".
However, when I use myWriter.write(data), it only writes the last line of the initial file.
My task is to read a file (in this case, filename.txt) and copy its content into a new file (new.txt).
package javaapplication13;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.io.PrintWriter;
import java.io.FileWriter;
import java.io.IOException;
public class readFile {
public static String data;
public static void main(String[] args) throws IOException{
try{
File myObj = new File("C:\\Users\\Admin\\Documents\\NetBeansProjects\\JavaApplication13\\src\\javaapplication13\\filename.txt");
try (Scanner myReader = new Scanner(myObj)) {
do{
data = myReader.nextLine();
}
while (myReader.hasNextLine());
PrintWriter out = new PrintWriter("C:\\Users\\Admin\\Documents\\NetBeansProjects\\JavaApplication13\\src\\javaapplication13\\new.txt");
FileWriter myWriter = new FileWriter("C:\\Users\\Admin\\Documents\\NetBeansProjects\\JavaApplication13\\src\\javaapplication13\\new.txt");
myWriter.write(data);
myWriter.close();
out.close();
myReader.close();
}
}
catch (FileNotFoundException e){
System.out.println("An error occurred.");
}
}
}
Every iteration of the loop opens a new writer, and then writes to it, thus overwriting the file. Instead, you should open the writer once, before the loop, and close it once you're done writing. E.g.:
try (FileWriter myWriter = new FileWriter("C:\\Users\\Admin\\Documents\\NetBeansProjects\\JavaApplication13\\src\\javaapplication13\\new.txt")) {
while (myReader.hasNextLine());
myWriter.write(myReader.nextLine());
}
}
I would like to create a new file using filewriter class and use the exact path in file class (don't want to copy/paste the manually, any changes in file writer path, we would like to reflect the instances) to get absolute path of the particular file. Can anyone suggest me how?
First I would create a filewriter and later want to use File to display it's attributes such that any chnages in Fiewriter URL would be displayed.
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
public class files_read {
public static void main(String[] args) {
// TODO Auto-generated method stub
try {
FileWriter FW=new FileWriter("C:/Users/91870/Downloads/Boss.txt");
FW.write("yoyo");
FW.close();
File f=new File(FW);
}
catch(IOException ie)
{
System.out.println("An error occurred.");
ie.printStackTrace();
}
}
}
You should do it the other way around. First create the File instance and then the FileWriter with that File instance.
File f = new File("C:/Users/91870/Downloads/Boss.txt");
FileWriter fw = new FileWriter(f);
...
I made the program in java to convert the text in the file in the uppercase but it erases data instead of converting it
But when I take data from 1 file and write converted data into another file, it works fine.
So I got problem that how can I do this using single file.
Here below is my code, Tell me how to correct this?
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.FileWriter;
public class uppercase{
public static void main(String[] args) {
try {
FileReader reader = new FileReader("e.txt");
FileWriter writer = new FileWriter("e.txt");
int data;
int data2;
while((data=reader.read())!= -1) {
data2=Character.toUpperCase(data);
writer.write(data2);
}
reader.close();
writer.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
this is bad idea, because you are writing to same file you are reading from. You should either:
Load complete file to memory, close it and then dump it to same file.
Save to different file and rename (better)
firstly you open a stream to read from file and append the result to a String variable and at the end of reading, you write all the data to the file:
try {
FileReader reader = new FileReader("e.txt");
String result = "";
int data;
int data2;
while ((data = reader.read()) != -1) {
data2 = Character.toUpperCase(data);
result += (char)data2;
}
reader.close();
System.out.println(result);
FileWriter writer = new FileWriter("e.txt");
writer.write(result);
writer.flush();
writer.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
I am unable to read the properties from the file . When I try to print it gives me null, When I debugged I understood it is not loading the file in function
pro.Load(). However my path is correct, still I am unable to load the file
package AdvancedJava;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Properties;
public class ReadingPropertiesFile {
public static void main(String[] args) throws FileNotFoundException {
Properties pro = new Properties();
String path = "C://Users//310259741//Documents//ProjectManagment//JavaBasics//object.properties";
// BufferedReader reader = new BufferedReader(new FileReader(path));
File f = new File(path);
FileInputStream fis = null;
try {
fis = new FileInputStream(f);
pro.load(fis);
}
catch (IOException e) {
System.out.println(e.getMessage());
}
System.out.println(pro.getProperty("lastname"));
}
}
Properties file contents
firstname = John
lastname = harry
Automation = Selenium
I think the problem is in path:
String path = "C://Users//310259741//Documents//ProjectManagment//JavaBasics//object.properties";
should be like this:
String path = "C:\\Users\\310259741\\Documents\\ProjectManagment\\JavaBasics\\object.properties";
Also make sure you have a correct path to your properties file. If it is inside your project, the path should be like this:
String path = "C:\\...\\ProjectFolder\\src\\main\\resources\\object.properties";
Your example works fine for me. Without a stacktrace though, we won't be able to help you regarding the NPE you're getting.
In any way though, I couple of hints regarding your code. I would suggest using a try - with resources when operating with the FileInputStream to make sure that the resource is going to be closed once done.
You can avoid using new File(path);. Instead I would suggest using Paths from the java.nio.* package. An example of this based on your code snippet would be the following:
public static void main(String[] args) {
Properties properties = new Properties();
try (FileInputStream stream = new FileInputStream(Paths.get("E:\\test\\file.txt").toFile())) {
properties.load(stream);
} catch (IOException e) {
e.printStackTrace();
}
System.out.println(properties.getProperty("lastname"));
}
The advantage of using Paths is that they're (if not mistaken) system agnostic meaning that you won't need to worry about providing the proper path delimiters.
Actually, path should be with another separator
"C:\\Users\\310259741\\Documents\\ProjectManagment\\JavaBasics\\object.properties";
but what I should suggest you - it's to store your app properties files under your resource folder, kinda:
src/main/resources/config.properties
than you gonna be able to access this file like this:
public Properties extractFrom(String fileName) {
Properties properties = new Properties();
try (InputStream inputStream = PropertiesExtractor.class
.getClassLoader().getResourceAsStream(fileName)) {
properties.load(inputStream);
} catch (IOException ex) {
throw new RuntimeException("Cannot load properties", ex);
}
return properties;
}
extractFrom("config.properties");
I've been trying to come up with a class that deletes a line from a text file that starts with a particular number.
What I currently have doesn't show any code errors and also runs without erros; shows "BUILD SUCCESSFUL" on netbeans, but doesn't do anything to the line, or any part of the textfile whatsoever, let alone delete the intended line.
Could anyone please look at my code and please advise me on what I might have done wrong, or is missing?
Thanks a lot in advance.
Heres my code:
package Database;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
public class Edit {
public void removeLineFromFile(String file, String lineToRemove) {
try {
File inFile = new File("/D:/TestFile.txt/");
if (!inFile.isFile()) {
System.out.println("Parameter is not an existing file");
return;
}
//Construct the new file that will later be renamed to the original filename.
File tempFile = new File(inFile.getAbsolutePath() + ".tmp");
BufferedReader br = new BufferedReader(new FileReader(file));
PrintWriter pw = new PrintWriter(new FileWriter(tempFile));
String line = null;
//Read from the original file and write to the new
//unless content matches data to be removed.
while ((line = br.readLine()) != null) {
if (!line.trim().equals(line.startsWith(lineToRemove))) {
pw.println(line);
pw.flush();
}
}
pw.close();
br.close();
//Delete the original file
if (!inFile.delete()) {
System.out.println("Could not delete file");
return;
}
//Rename the new file to the filename the original file had.
if (!tempFile.renameTo(inFile))
System.out.println("Could not rename file");
}
catch (FileNotFoundException ex) {
ex.printStackTrace();
}
catch (IOException ex) {
ex.printStackTrace();
}
}
public static void main(String[] args) {
Edit edit = new Edit();
edit.removeLineFromFile("/D:/TestFile.txt/", "2013001");
}
}
There is a problem with your logic ... you are saying if the line equals to itself that starts with something which will never happen unless the line only consist of the line you want to remove
if (!line.trim().equals(line.startsWith(lineToRemove))
i think needs to be just
if (!line.startsWith(lineToRemove))
Change the if condition to:
if (!line.startsWith(lineToRemove)) {
pw.println(line);
pw.flush();
}