So I have the following code where I should read a Text File (This is just the Main Class):
import gui.MenuWindow;
import java.io.IOException;
import javax.swing.JOptionPane;
public class Assessor {
public static void main(String args[]) throws IOException {
FileLoader file = new FileLoader("Example.txt");
try{
new MenuWindow(file.loader());
} catch(Exception exc) {
JOptionPane.showMessageDialog(null, "Error Reading File");
}
}
}
Then I'd have to load the Text into a ListBox using Swing. The thing is that I've found this new code to read a Text File:
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.io.IOException;
public class ReadTextFileExample {
public static void main(String[] args) {
File file = new File("test.txt");
StringBuffer contents = new StringBuffer();
BufferedReader reader = null;
try {
reader = new BufferedReader(new FileReader(file));
String text = null;
// repeat until all lines is read
while ((text = reader.readLine()) != null) {
contents.append(text)
.append(System.getProperty(
"line.separator"));
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
// show file contents here
System.out.println(contents.toString());
}
}
So I'd like to know what is the difference between the following two lines:
FileLoader file = new FileLoader("Example.txt"); //First Code
File file = new File("test.txt"); //Second Code
And... What's the StringBuffer and BufferedReader used to? Thanks!
So I'd like to know what is the difference between the following two lines:
FileLoader file = new FileLoader("Example.txt"); //First Code
File file = new File("test.txt"); //Second Code
The first creates a java.io.FileLoader which Andreas discusses. Since the javadoc says "The constructors of this class assume that the default character encoding and the default byte-buffer size are appropriate", it should never be used.
The second creates a java.io.File which is just a file path with some utility methods that can be used to read directory trees, delete, create, and move files, etc., or it can be used with FileInputStream and other classes to actually access the file contents.
And... What's the StringBuffer and BufferedReader used to? Thanks!
The StringBuffer is used to collect the contents of the file.
The BufferedReader is used to speed up reading of the file. Instead of reading one character at a time, the BufferedReader batches reads using an internal buffer.
This is an exemplary question about learning Java SE, especially regarding the java.io package. I was a bit puzzled in the beginning, but now I am quite sure that you want to compare the FileReader to the File class, which both belong to the same package java.io.
File in the Java SE API:"An abstract representation of file and directory pathnames."In other words, it is there to handle files and directories on the file system within Java. Since Java is an object-oriented language, they made a class for it. Files, i.e. binary and text files, share some attributes in common with directories, as there are: absolute, canonical path and simple name, etc.Of course, File is one of the base classes in the java.io package and many classes like FileReader make use of it for object construction.
FileReader:"Convenience class for reading character files."It comes with a handy constructor that takes a file name or file path as a String. Originally, it was meant to be constructed by a File instance. A Reader instance in general is practical to read text files, in contrast to InputStream, which is used to read binary files. A Reader instance in general is connected to a character set, e.g. "UTF-8" to translate byte to character streams.
Please also have a look at the excellent Java Tutorials provided by Oracle.
I hope the difference between File and FileReader becomes a little clearer. Especially note that there is no I/O, when you instantiate a File instance. To answer your question, the interconnection of the two classes would be:
File file = new File("test.txt"); // 1) Instaniate the file
Reader reader = new FileReader(file); // 2) Instantiate the Reader using the File instance
When you wrap a BufferedReader around a Reader instance, you can read the text file linewise, as:
BufferedReader bufferedReader = new BufferedReader(reader); // 3) Get a "buffered reader" to have access line by line.
StringBuffer comes in, when you want to chain a large number of String objects, since String objects is immutable and string operations like
String s1 = "Star ";
String s2 = "Wars";
s1 = s1 + s2;
are very costly, especially in loops, since at every addition a new String object (left side result) is created, with practically no size limits, apart from the reserved Java VM heap space.
Let me point out that you should better use the StringBuilder class, which is even faster, and is the unsynchronized counter-part of StringBuffer, introduced in the Java 5 release. The feature that StringBuffer is guaranteed to be synchronized among different Thread's is hardly ever used. I never came across it in my whole life as Java programmer.
Related
I used a regular expression to parse a text file to use the resulted group one and two as follows:
write group two in another file
make its name to be group one
Unfortunately, No data is written on the file!
I did not figure out where is the problem, here is my code:
package javaapplication5;
import java.io.*;
import java.util.regex.*;
public class JavaApplication5 {
public static void main(String[] args) {
// TODO code application logic here
try {
FileInputStream fstream = new FileInputStream("C:/Users/Welcome/Desktop/End-End-Delay.txt");
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
File newFile1= new File("C:/Users/Welcome/Desktop/AUV1.txt");
FileOutputStream fos1= new FileOutputStream(newFile1);
BufferedWriter bw1= new BufferedWriter(new OutputStreamWriter(fos1));
String strLine;
while ((strLine = br.readLine()) != null) {
Pattern p = Pattern.compile("sender\\sid:\\s(\\d+).*?End-End\\sDelay:(\\d+(?:\\.\\d+)?)");
Matcher m = p.matcher(strLine);
while (m.find()) {
String b = m.group(1);
String c = m.group(2);
int i = Integer.valueOf(b);
if(i==0){
System.out.println(b);
bw1.write(c);
bw1.newLine();
}
System.out.println(b);
// System.out.println(c);
}
}
}
catch (Exception e) {
System.err.println("Error: " + e.getMessage());
}
}
}
Can anyone here help me to solve this problem and Identify it?
You are using BufferedWriter, and never flush (flushing writer pushes the contents on disk) your writer or even close it at the end of your program.
Due to which, before your content gets written in actual file on disk from BufferedWriter, the program exits and the contents get lost.
To avoid this, either you can call flush just after writing contents in bw1,
bw1.write(c);
bw1.newLine();
bw1.flush();
OR
Before your program ends, you should call,
bw1.close(); // this ensures all content in buffered writer gets push to disk before jvm exists
Calling flush every time you write the data is not really recommended, as it defeats the purpose of buffered writing.
So best is to close the buffered writer object. You can do it in two ways,
Try-with-resources
Manually close the buffered writer object in the end, likely in the finally block so as to ensure it gets called.
Besides all this, you need to ensure that your regex matches and your condition,
if(i==0){
gets executed else code that is writing data in file won't get executed and of course in that case no write will happen in file.
Also, it is strongly recommended to close any of the resources you open like file resources, database (Connection, Statements, ResultSets) resources etc.
Hope that helps.
I have two different ways to read the file but I am not sure how to proceed to converting the text to a string and then an if then statement like...
if string contains ":"
true string = "string"
false string = ,,"string"
package test;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
public class ReadStringFromFileLineByLine {
public static void main(String[] args) {
try {
File file = new File("foo.txt");
FileReader fileReader = new FileReader(file);
BufferedReader bufferedReader = new BufferedReader(fileReader);
StringBuffer stringBuffer = new StringBuffer();
String line;
String trim;
while ((line = bufferedReader.readLine()) != null) {
stringBuffer.append(line);
stringBuffer.append("\n");
}
fileReader.close();
System.out.println("Contents of file:");
System.out.println(stringBuffer.toString());
} catch (IOException e) {
e.printStackTrace();
}
}
}
But I don't believe I am using the trim command appropriately
Your question doesn't really communicate clearly the intent of the program. What exactly are you trying to do? If your file is text-based, there is no "conversion to String" needed. Also "save the file as an output" isn't clear either. Do you want to save a new file, overwrite the existing file, or append the existing file. All of these scenarios are handled differently. Taking this by parts:
First point: Your Scantest class works. Given a file foo.txt in the project folder, the class will print out the contents of the file.
Second point: Your class ReadStringFromFileLineByLine works with my own foo.txt just like the first class. So, there might be something wrong with your test.txt file. This is probably the most important thing when testing (making all conditions equal). If the conditions for testing are not equal, the tests will most likely be inconclusive (which is why I suspect happened in your case).
Third point: None of your classes attempted to make any modifications to the obtained strings or made modifications to the file. If you were to write to a file, you have to consider the following: Append vs. Overwrite. All it takes is the use of a simple boolean value:
FileWriter fw = new FileWriter(file.getAbsoluteFile()); // overwrites contents of file
FileWriter fw = new FileWriter(file.getAbsoluteFile(), true); // appends to file
The FileWriter single argument contructor calls the two-argument constructor passing false to it. Therefore, the FileWriter overwrites instead of appends. This is important because if you handle the file line by line, it is possible that at the end, your file will contain only the last line you "modified." If you choose to append, the new String will be added to the end of the line. So this is not good either. If you want to process a file line by line, made modifications to any given line, AND save the line to the same file, your best option is to use RandomAccessFile. This class allows you to write 'X' number of characters starting on a given offset. In this case, this "offset" is the "address" of the current line; putting it simply: the offset is equal to the number of characters already processed. So, for the first line, the offset is 0, for line 2 is the number of characters in line 1, and so forth.
I can add this as an update if you need it, but I did not see anything in your code that attempted to change the file in any way. I was just going by your title.
I wrote a simple program to read the content from text/log file to html with conditional formatting.
Below is my code.
import java.io.*;
import java.util.*;
class TextToHtmlConversion {
public void readFile(String[] args) {
for (String textfile : args) {
try{
//command line parameter
BufferedReader br = new BufferedReader(new FileReader(textfile));
String strLine;
//Read File Line By Line
while ((strLine = br.readLine()) != null) {
Date d = new Date();
String dateWithoutTime = d.toString().substring(0, 10);
String outputfile = new String("Test Report"+dateWithoutTime+".html");
FileWriter filestream = new FileWriter(outputfile,true);
BufferedWriter out = new BufferedWriter(filestream);
out.write("<html>");
out.write("<body>");
out.write("<table width='500'>");
out.write("<tr>");
out.write("<td width='50%'>");
if(strLine.startsWith(" CustomerName is ")){
//System.out.println("value of String split Client is :"+strLine.substring(16));
out.write(strLine.substring(16));
}
out.write("</td>");
out.write("<td width='50%'>");
if(strLine.startsWith(" Logged in users are ")){
if(!strLine.substring(21).isEmpty()){
out.write("<textarea name='myTextBox' cols='5' rows='1' style='background-color:Red'>");
out.write("</textarea>");
}else{
System.out.println("else if block:");
out.write("<textarea name='myTextBox' cols='5' rows='1' style='background-color:Green'>");
out.write("</textarea>");
} //closing else block
//out.write("<br>");
out.write("</td>");
}
out.write("</td>");
out.write("</tr>");
out.write("</table>");
out.write("</body>");
out.write("</html>");
out.close();
}
//Close the input stream
in.close();
}catch (Exception e){//Catch exception if any
System.err.println("Error: " + e.getMessage());
e.printStackTrace();
}
}
}
public static void main(String args[]) {
TextToHtmlConversion myReader = new TextToHtmlConversion();
String fileArray[] = {"D:/JavaTesting/test.log"};
myReader.readFile(fileArray);
}
}
I was thinking to enhance my program and the confusion is of either i should use Maps or properties file to store search string. I was looking out for a approach to avoid using substring method (using index of a line). Any suggestions are truly appreciated.
From top to bottom:
Don't use wildcard imports.
Don't use the default package
restructure your readFile method in more smaller methods
Use the new Java 7 file API to read files
Try to use a try-block with a resource (your file)
I wouldn't write continuously to a file, write it in the end
Don't catch general Exception
Use a final block to close resources (or the try block mentioned before)
And in general: Don't create HTML by appending strings, this is a bad pattern for its own. But well, it seems that what you want to do.
Edit
Oh one more: Your text file contains some data right? If your data represents some entities (or objects) it would be good to create a POJO for this. I think your text file contains users (right?). Then create a class called Users and parse the text file to get a list of all users in it. Something like:
List<User> users = User.parse("your-file.txt");
Afterwards you have a nice user object and all your ugly parsing is in one central point.
I'm trying to write a program that reads a file (which is a Java source file), makes an Arraylist of certain specified values from that file. and outputs that Arraylist into another resulting file.
I'm using PrintWriter to make the new resulting file. This is a summarised version of my program:
ArrayList<String> exampleArrayList = new ArrayList<String>();
File actualInputFile = new File("C:/Desktop/example.java");
PrintWriter resultingSpreadsheet= new PrintWriter("C:/Desktop/SpreadsheetValues.txt", "UTF-8");
FileReader fr = new FileReader(actualInputFile);
BufferedReader br = new BufferedReader(fr);
String line=null;
while ((line = br.readLine()) != null) {
// code that makes ArrayList
}
for (int i = 0; i < exampleArrayList.size(); i++) {
resultingSpreadsheet.println(exampleArrayList.get(i));
}
resultingSpreadsheet.close();
The problem is that when i run this, nothing gets printed to the resultingSpreadsheet. It's completely empty.
BUT, this program works perfectly (meaning that it prints out everything correctly to the resultingSpreadsheet file) when I replace:
File actualInputFile = new File("C:/Desktop/example.java");
which is the file that I want as my input file, and which has a size of 481 KB,
with:
File smallerInputFile = new File("C:/Desktop/smallerExample.txt");
which is really just a smaller .txt example version of the .java source file, and it has a size of 1.08 KB.
I've tried a few things including flushing the PrintWriter, wrapping it around FileWriter, copy-pasting all the code from the .java file into a text file in case it was an extension problem, but these don't seem to work.
I'm starting to think it must be because of the size of the file that the PrintWriter makes, but it's very possible that that's not the problem. Perhaps I need to put everything in a stream (like it says here: http://docs.oracle.com/javase/6/docs/api/java/io/PrintWriter.html)? If so, how would I do that?
Why is reading the bigger actualInputFile and outputting its data correctly such a problem, when everything works fine for the smallerInputFile?
Can anyone help with this?
Check for exceptions while writing to the the excel sheet , because i really don't think its a problem of size. Below is the sample code that is executing successfully and the file size was approx 1 MB.
public class Test {
/**
* #param args
*/
public static void main(String[] args) {
BufferedReader br = null;
try {
String sCurrentLine;
br = new BufferedReader(new FileReader("D:\\AdminController.java"));
while ((sCurrentLine = br.readLine()) != null) {
System.out.println(sCurrentLine);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (br != null)br.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
}
This should go as a comment, but I do not have the rep. In the documentation it has both write methods and print methods. Have you tried using write() instead?
I doubt it's the size of the file, it may be between the two files you are testing one is .txt, and the other is .java
EDIT: Probably second suggestion of the two. First is just something I noticed with the docs.
The methods of PrintWriter do not throw Exception. Call the checkError() method which would flush the stream as well as return true if an error occurred. It is quite possible that an error occurred processing the larger file, an encoding error for instance.
Check your program. When the file is empty it means that your program doesn't close the PrintWriter before finishing the program.
For example you may have a return in a part of your program which cause that resultingSpreadsheet.close(); have not being run.
I'm learning File I/O using Java.
Following are my codes from two different Java files. One is "File" with the main class, the other is "FileWrite."
I was able to implement string input and output. But the output textfile has gibberish in the beginning and I am not sure why.
[File.Java]
package file;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
public class File {
public static void main(String[] args) {
try (BufferedReader br = new BufferedReader(new FileReader("B:\\fileIn.txt")))
{
String stCurrent;
while ((stCurrent = br.readLine()) != null) {
System.out.println(stCurrent);
}
} catch (IOException e) {
e.printStackTrace();
}
FileWrite fW = new FileWrite();
fW.serializeAddress("Boston", "Canada");
}
}
[FileWrite.Java]
package file;
import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
public class FileWrite {
public void serializeAddress(String city, String country) {
try {
FileOutputStream fout = new FileOutputStream("B:\\address.txt");
ObjectOutputStream obOut = new ObjectOutputStream(fout);
obOut.writeUTF(city);
obOut.writeUTF(country);
obOut.close();
System.out.println("Output Done");
} catch(Exception ex) {
ex.printStackTrace();
}
}
}
Now, on "obOut.writeUTF(city); obOut.writeUTF(country);" I separated out two string inputs. Is there a way to combine them into one? As in obOut.writeUTF(city, counry) instead of two. Or is this only achievable through making these into an object?
[Update]
Imported a couple more and I tried
PrintStream ps = new PrintStream(new FileWriter("B:\\addressPS.txt"));
ps.println(city);
ps.println(country);
ps.close();
But with errors, any clue?
You are doing the right thing keeping them separate already. City and country are different fields.
A very common mistake is not making a distinction between binary and text files/socket streams. You are a mixing the two which will lead to confusion. I suggest you only sue text Writer/Reader or binary Input/OuptutStream unless you have a very clear idea of what you are doing.
In short if you what to write text use
PrintStream ps = new PrintStream(new FileWriter(textFileName));
ps.println(city);
ps.println(country);
ps.close();
writeUTF takes strings also, you don't have to create new object for city and county.
Cant you do obOut.writeUTF(city +" "+country); ?
The gibberish is because .writUTF() writes data in a modified UTF format which is mentioned in the javadocs.
An ObjectOutputStream is generally used to output OBJECTS but I suppose you can use it for strings as well. You can use the respective .readUTF() method in the ObjectInputStream class in order to read the data in your file back.
Also, you have tried to use the try-with-resources block which is new to Java SE7. You should NOT do it the way you have done so. You should do this instead:
try (FileReader fr = new FileReader("B:\\fileIn.txt"); BufferedReader br = new BufferedReader(fr);) {
} catch (FileNotFoundException e1) {
e1.printStackTrace();
} catch (IOException e1) {
e1.printStackTrace();
}
Splitting the FileReader and the BufferedReader will allow Java SE7 to close both the streams with ease. The way you have done it, only the BufferedReader stream will get closed after the try block finishes.
By definition, ObjectOutputStream produces 'gibberish'. It's not intended for human consumption, it is a format used to write out objects so that you can read them back. You're not supposed to be able to make sense of the results in a text editor. To make human-readable content, just use an OutputStreamWriter or even a PrintWriter. In short, your last example is correct, and if you get errors, please edit your question to tell us what the errors are.