So I'm trying to practice connecting out of one java program to the input of another program and I'm wondering if the way I did it is efficient or if there's a better way. I'm saving a string into a text file in the first program and reading the string then printing it out in the second. Is there a way to just cut out using the text file as a middle man?
Here's my first program:
import java.util.Scanner;
import java.io.*;
public class pip1{
public static void main(String[] args){
String inString = "";
Scanner sc = new Scanner(System.in);
inString = sc.next();
try{
PrintWriter out = new PrintWriter("word.txt");
out.println(inString);
out.close();
} catch(FileNotFoundException ex){ }
}
}
and here is the second:
import java.io.*;
public class pip2{
public static void main(String[] args) {
String fileName = "word.txt";
try {
FileReader fr = new FileReader(fileName);
BufferedReader br = new BufferedReader(fr);
String outString = br.readLine();
br.close();
fr.close();
System.out.println(outString);
} catch (FileNotFoundException ex) {}
catch (IOException ex) {}
}
}
Thanks!
I suppose what you want is a pipe, which acts as a "intermediate wire" between two processes without using an "temporary file".
So I recommend you to read doc about Pipes in JAVA.
Here's a link of tutorial.
Also see javadoc about PipedInputStream
javadoc about PipedOutputStream
What's more, if your OS supports IO redirection from terminal, then just do it without using , as Andy says. This would be the easiest.
Just write to System.out in the first one, read from System.in in your second, and use a pipe to connect the output of the first into the second when you run the two commands:
java pip1 | java pip2
Related
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 currently have the follow method:
try {
URL url = new URL("http://auth.h.gp/HAKUNA%20MATATA.txt");
Scanner s = new Scanner(url.openStream());
}
catch(IOException ex) {
BotScript.log("Something went wrong =/ Error code:");
ex.printStackTrace();
stop();
}
However, how do I check if it contains a word? I've never worked with Scanners before and I found this snippet online.
Thank you.
Okay, that looks good so far.
You can then use Scanner's next() method to get each word. You can also query hasNext() to see if there's another token available to avoid errors.
boolean foundPumbaa = false;
while (s.hasNext()) {
if (s.next().equalsIgnoreCase("pumbaa")) {
foundPumbaa = true;
System.out.println("We found Pumbaa"); // do something
break;
}
}
if (!foundPumbaa) {
System.out.println("We didn't find Pumbaa");
}
EDIT in response to comment:
Yes, you can turn the text into a String. The best way to do this is probably with a BufferedReader.
From the Java Tutorial, "Reading Directly from a URL":
The following small Java program uses openStream() to get an input
stream on the URL http://www.oracle.com/. It then opens a
BufferedReader on the input stream and reads from the BufferedReader
thereby reading from the URL. Everything read is copied to the
standard output stream:
import java.net.*;
import java.io.*;
public class URLReader {
public static void main(String[] args) throws Exception {
URL oracle = new URL("http://www.oracle.com/");
BufferedReader in = new BufferedReader(
new InputStreamReader(oracle.openStream()));
String inputLine;
while ((inputLine = in.readLine()) != null)
System.out.println(inputLine);
in.close();
}
}
In a real program, instead of main throws Exception, you'd have that in a try-catch block and catch an IOException and some various URLExceptions. But this should get you started.
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.
I have a file, I know that file will always contain only one word.
So what should be the most efficient way to read this file ?
Do i have to create input stream reader for small files also OR Is there any other options available?
Well something's got to convert bytes to characters.
Personally I'd suggest using Guava which will allow you to write something like this:
String text = Files.toString(new File("..."), Charsets.UTF_8);
Obviously Guava contains much more than just this. It wouldn't be worth it for this single method, but it's positive treasure trove of utility classes. Guava and Joda Time are two libraries I couldn't do without :)
Use Scanner
File file = new File("filename");
Scanner sc = new Scanner(file);
System.out.println(sc.next()); //it will give you the first word
if you have int,float...as first word you can use corresponding function like nextInt(),nextFloat()...etc.
Efficient you mean performance-wise or code simplicity (lazy programmer)?
If it is the second, then nothing I know beats:
String fileContent = org.apache.commons.io.FileUtils.readFileToString("/your/file/name.txt")
- Use InputStream and Scanner for reading the file.
Eg:
public class Pass {
public static void main(String[] args){
File f = new File("E:\\karo.txt");
Scanner scan;
try {
scan = new Scanner(f);
while(scan.hasNextLine()){
System.out.println(scan.nextLine());
}
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
- Guava Library handles this beautifully and efficiently.
Use BufferedReader and FileReader classes. Only two lines of code will suffice to read one word/one line file.
BufferedReader br = new BufferedReader(new FileReader("Demo.txt"));
System.out.println(br.readLine());
Here is a small program to do so. Empty file will cause to print 'null' as output.
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
public class SmallFileReader
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new FileReader("Demo.txt"));
System.out.println(br.readLine());
}
}
import java.io.*;
import java.util.*;
public class Readfilm {
public static void main(String[] args) throws IOException {
ArrayList films = new ArrayList();
File file = new File("filmList.txt");
try {
Scanner scanner = new Scanner(file);
while (scanner.hasNext())
{
String filmName = scanner.next();
System.out.println(filmName);
}
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}
}}
Above is the code I'm currently attempting to use, it compiles fine, then I get a runtime error of:
java.util.NoSuchElementException
at java.util.Scanner.throwFor(Scanner.java:907)
at java.util.Scanner.next(Scanner.java:1416)
at Readfilm.main(Readfilm.java:15)
I've googled the error and not had anything that helped (I only googled the first 3 lines of the error)
Basically, the program I'm writing is part of a bigger program. This part is to get information from a text file which is written like this:
Film one / 1.5
Film two / 1.3
Film Three / 2.1
Film Four / 4.0
with the text being the film title, and the float being the duration of the film (which will have 20 minutes added to it (For adverts) and then will be rounded up to the nearest int)
Moving on, the program is then to put the information in an array so it can be accessed & modified easily from the program, and then written back to the file.
My issues are:
I get a run time error currently, not a clue how to fix? (at the moment I'm just trying to read each line, and store it in an array, as a base to the rest of the program) Can anyone point me in the right direction?
I have no idea how to have a split at "/" I think it's something like .split("/")?
Any help would be greatly appreciated!
Zack.
Your code is working but it reads just one line .You can use bufferedReader here is an example import java.io.*;
class FileRead
{
public static void main(String args[])
{
try{
// Open the file that is the first
// command line parameter
FileInputStream fstream = new FileInputStream("textfile.txt");
// Get the object of DataInputStream
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String strLine;
//Read File Line By Line
while ((strLine = br.readLine()) != null) {
// Print the content on the console
System.out.println (strLine);
}
//Close the input stream
in.close();
}catch (Exception e){//Catch exception if any
System.err.println("Error: " + e.getMessage());
}
}
}
And here is an split example class StringSplitExample {
public static void main(String[] args) {
String st = "Hello_World";
String str[] = st.split("_");
for (int i = 0; i < str.length; i++) {
System.out.println(str[i]);
}
}
}
I wouldn't use a Scanner, that's for tokenizing (you get one word or symbol at a time). You probably just want to use a BufferedReader which has a readLine method, then use line.split("/") as you suggest to split it into two parts.
Lazy solution :
Scanner scan = ..;
scan.nextLine();