I have instantiated a BufferedReader to read an input stream. It has a boolean ready() method that returns false until the reader can be read. Now I have
BufferedReader br = new BufferedReader(new InputStreamReader(myProcess.getInputStream()));
try {
while (!br.ready()) {
}
String line = br.readLine();
...
} catch (IOException e) {
...
What PMD warns me about is the empty while block and I guess PMD is right. How can I rewrite the code?
you don't want to use ready(). readLine() is a blocking call, just call it.
the standard usage of BufferedReader is:
String line = null;
while((line = br.readLine) != null) {
// do stuff with line here ...
}
You could try this:
BufferedReader br = new BufferedReader(new InputStreamReader(myProcess.getInputStream()));
try {
String line;
while ( null != (line = br.readLine() )) {
...
}
...
} catch (IOException e) { ... }
A way to rewrite it is
while(!br.ready());
But a more readable way to do this is to read only when the buffer is ready
while(br.ready()){
String line = br.readLine();
...
}
Related
I am getting data from php file in android java class using
BufferedReader reader = new BufferedReader(new
InputStreamReader(con.getInputStream()));.
This code is in my php file is
echo "abc";
echo "xyz";
This is the code of my java file.
BufferedReader reader = new BufferedReader(new InputStreamReader(con.getInputStream()));
String line = null;
Complete_line = null;// Read Server Response
while ((line = reader.readLine()) != null) {
System.out.println(line);
break;
}
But when I read from Buffer reader it will read a whole one line, or it will print "line" string as "abcxyz". But I want them as two lines as they are two different lines in the PHP file.
try this,
BufferedReader reader = null;
StringBuffer response = new StringBuffer();
try {
reader = new BufferedReader(new InputStreamReader(in));
String line = "";
while ((line = reader.readLine()) != null) {
response.append(line+"\n");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
In PHP, unless you seperate the 2 lines a a newline character \n, the two echos are the same. To seperate echos into different lines, you need to end the strings with \n, like this:
echo "abc\n";
echo "xyz\n";
Isn't there a cleaner way of doing the following (eliminating the need for initializing line prior to the while block)? It just seems unnecessary to intialize a variable prior to its usage instead of doing something like while ((String line = br.readLine) != null) {}. If not, why not?
BufferedReader reader = null;
try
{
File file = new File("sample-file.dat");
reader = new BufferedReader(new FileReader(file));
String line;
while ((line = reader.readLine()) != null)
{
System.out.println(line);
}
}
catch (IOException e)
{
e.printStackTrace();
}
finally
{
try
{
reader.close();
}
catch (IOException e)
{
e.printStackTrace();
}
}
No, you cannot avoid initializing the variable. However, you can use Try-With-Resources to make it a lot cleaner.
try (BufferedReader reader = new BufferedReader(new FileReader("sample-file.dat"))) {
String line;
while ((line = reader.readLine()) != null)
{
System.out.println(line);
}
}
catch (IOException e)
{
e.printStackTrace();
}
Just adding this for completions sake, if anyone is using Java 8, you have access to the Stream API. Using this you can just simply do the following:
BufferedReader reader = new BufferedReader(...);
reader.lines().forEach(System.out::println);
And if you're wondering, the code under the hood that produces this does check for null lines.
No you can't declare (and use) a variable in the while loop expression evaluation step. But, you can eliminate the finally block by using a try-with-resources
try (
File file = new File("sample-file.dat");
BufferedReader reader = new BufferedReader(new FileReader(file));
) {
String line;
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
No, you can't declare a variable inside the condition definition except in a for loop. Can't really say why - perhaps because the condition is not supposed to be somewhere you initialize things, whereas a for initialization step is.
But anyway, especially in cases where the loop conditions are complicated, some coders prefer to use
while (true) {
String line = reader.readLine();
if ( line == null )
break;
System.out.println(line);
}
But it's really a matter of style.
I have method which writes some data to file. I use PrintWriter, BufferedWriter and FileWriter as shown below
public void writeToFile(String FileName){
PrintWriter pw = null;
try {
pw = new PrintWriter(new BufferedWriter(new FileWriter(FileName)));
for(Cars car : list){
pw.println(car.getType());
pw.println(car.getMaxSpeed());
pw.println(car.getOwner());
pw.println();
pw.flush();
}
pw.close();
}
catch(IOException ex){
System.err.println(ex);
}
}
Now how can I read this data from file? I tried to use InputStreamReader, BufferedReader and FileInputStream, but my NetBeans shows me an error message
public void readFromFile() throws IOException {
InputStreamReader fr = null;
try {
fr = new InputStreamReader(new BufferedReader(new FileInputStream(new FileReader("c:\\cars.txt"))));
System.out.println(fr.read());
} catch (Exception ex) {
System.out.println(ex.getMessage());
} finally {
fr.close();
}
}
What is wrong with this method?
BufferedReader in = new BufferedReader(new FileReader("file.in"));
BufferedWriter out = new BufferedWriter(new FileWriter("file.out"));
String line = in.readLine(); // <-- read whole line
StringTokenizer tk = new StringTokenizer(line);
int a = Integer.parseInt(tk.nextToken()); // <-- read single word on line and parse to int
out.write(""+a);
out.flush();
There are several problems in your code :
1) An InputStreamReader takes an InputStream as an argument not a Reader. See http://docs.oracle.com/javase/6/docs/api/java/io/InputStreamReader.html.
2) The FileInputStream does not accept a Reader as argument as well (it takes a File, a FileDescriptor, or a String). See : http://docs.oracle.com/javase/6/docs/api/java/io/FileInputStream.html
3) A BufferedReader reads the File line by line normally. The read() method only reads a single character.
A possible solution could be :
fr = new BufferedReader(new InputStreamReader(new FileInputStream(new File("c:\\cars.txt"))));
String line = "";
while((line = fr.readLine()) != null) {
System.out.println(line);
}
Btw : It would be easier for others to help you, if you provide the exact error-message or even better the StackTrace.
Simple error: Cannot resolve constructor 'FileInputStream(java.io.FileReader)', required constructor not exist in API.
Your original code was:
new PrintWriter(new BufferedWriter(new FileWriter(FileName)));
so for reading, you need
new PrintReader(new BufferedReader(new FileReader(FileName)));
but PrintReader is not needed (not exist), so all you need is:
new BufferedReader(new FileReader(FileName))
PrinterWriter prints formatted representations of objects to a text-output stream, but when reading text is always formatted, so PrinterReader not exist.
You are writing line by line, so also read line by line :) Example:
public void readFromFile() throws IOException {
BufferedReader bufferedReader = null;
try {
String sCurrentLine;
bufferedReader = new BufferedReader(new FileReader("c:\\cars.txt"));
while ((sCurrentLine = bufferedReader.readLine()) != null) {
System.out.println(sCurrentLine);
}
} catch (Exception ex) {
System.out.println(ex.getMessage());
} finally {
bufferedReader.close();
}
}
or better (JDK7)
void readFromFile() throws IOException {
Path path = Paths.get("c:\\cars.txt");
try (BufferedReader reader = Files.newBufferedReader(path, Charset.defaultCharset())){
String line = null;
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
}
}
everyone, I have a process that needs to get standard output and log/error/exception output from the subprocess. The standard output is fine, but I can't get ErrorStream, therefore the program is stuck there because of that. Here is my simple code. There is nothing magic, but why can't I get the error stream here? Thanks for looking at it.
BufferedReader standard =
new BufferedReader(new InputStreamReader(process.getInputStream()));
BufferedReader error =
new BufferedReader(new InputStreamReader(process.getErrorStream()));
String line = null;
while ((line = standard.readLine()) != null) {
System.out.println(line);
}
while ((line = error.readLine()) != null) {
System.out.println(line);
}
Now, as suggested, i used two threads to process the output and error streams, but still had the same problem, as follows. Can anybody give me some insights? Thanks.
ProcessBuilder pb = new ProcessBuilder(listArgs);
pb.redirectErrorStream();
Process process = pb.start();
StreamThread output = new StreamThread(process.getInputStream());
StreamThread error = new StreamThread(process.getErrorStream());
output.start();
error.start();
while (true) {
try {
output.join();
break;
}
catch (InterruptedException ie) {
ie.printStackTrace();
}
}
The definition of the StreamThread:
public static class StreamThread extends Thread{
private InputStream input = null;
public StreamThread(InputStream in){
input = in;
}
String line = null;
public void start(){
BufferedReader reader = new BufferedReader(new InputStreamReader(input));
try{
while( (line=reader.readLine()) != null ){
System.out.println(line);
}
reader.close();
}catch (IOException e){
e.printStackTrace();
}
}
}
Look at your loops:
while ((line = standard.readLine()) != null) {
System.out.println(line);
}
while ((line = error.readLine()) != null) {
System.out.println(line);
}
You're going to keep reading from the output stream until it's finished - which is likely to be when the process terminates. Only then do you start reading the error stream.
You should probably put at least one of these into a different thread, so you can read from both streams at the same time.
I have a text file and a class (Reader) that reads the text file and stores each line in a String [].
String name;
String [] lines;
Reader(String name){
this.name = name;
}
public String toString(){
return this.name;
}
public readFile(String filename){
String line = "";
int i = 0;
try{
BufferedReader reader = new BufferedReader(new FileReader(filename));
while(line = reader.readLine()) != null){
lines[i] = line;
i++;
}// while
reader.close();
}
catch(etc...){}
}
I wish to print each array element in table on my jsp page.
Reader r = new Reader("test");
out.print(r.toString());
works and prints 'test' but...
r.readFile("test.txt")
for (int i=0; i < r.lines.length; i++)
out.print(r.lines[i])
does not... However if I run this on the command line its prints the lines [ ] fine
How do I go about doing it in web context?
Try replacing the following:
BufferedReader reader = new BufferedReader(new FileReader(filename));
with
BufferedReader reader = new BufferedReader(new InputStreamReader(this.getClass().getResourceAsStream(filename)));
That should work since the input file is in the same package as Reader.
Update:
I think the problem lies in the TeamData.
readFile("skytest\\data.file")
That's not a valid path to the file. Neither in filesystem, nor in the classpath.
Since, the data.file is in the classpath, you can use getResourceAsStream to load it.
And, since skytest is the root directory (package), "/skytest/data.file" would also be valid here (the leading / means relative package root). Or, since the file lies in the same package as the TeamData, just the file name should be enough "data.file".
So, use of the following:
readFile("data.file")
And change the following:
BufferedReader reader = new BufferedReader(new FileReader(requiredFile));
to
BufferedReader reader = new BufferedReader(new InputStreamReader(this.getClass().getResourceAsStream(requiredFile)));
Also, the following is really a bad practice (that's called swallowing the exception):
catch (IOException ioe) {
//do something about the exception here
return false;
}
Try something like this:
BufferedReader reader = null;
try
{
reader = new BufferedReader(new FileReader(new File("path/to/filename.txt")));
String nextLine = reader.readLine();
while (nextLine != null)
{
System.out.println(nextLine); // do stuff with the line you read in.
nextLine = reader.readLine();
}
reader.close();
}
catch (FileNotFoundException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}