How to convert FileInputStream into string in java?

Question

In my java project, I'm passing FileInputStream to a function, I need to convert (typecast FileInputStream to string), How to do it.??

public static void checkfor(FileInputStream fis) {
 String a=new String;
 a=fis //how to do convert fileInputStream into string
 print string here
}

• Nikolay Kuznetsov: what are you trying to achieve? naive is fis.toString();
• akaIDIOT: Well, there's always, fis.toString(), though that might probably not what you wanted. Why would you want to turn fis into a String?
• Arpit: you want the content of file input stream into string ?
• the_marcelo_r: Here's a good resource for you to start: docs.oracle.com/javase/tutorial/essential/io
• Puce: Note: It's recommended to use the new NIO.2 File API instead of FileInputStream: docs.oracle.com/javase/tutorial/essential/io/file.html

Answer 1

You can't directly convert it to string. You should implement something like this Add this code to your method

 //Commented this out because this is not the efficient way to achieve that
 //StringBuilder builder = new StringBuilder();
 //int ch;
 //while((ch = fis.read()) != -1){
 // builder.append((char)ch);
 //}
 // 
 //System.out.println(builder.toString());

Use Aubin's solution:

public static String getFileContent(
 FileInputStream fis,
 String encoding ) throws IOException
 {
 try( BufferedReader br =
 new BufferedReader( new InputStreamReader(fis, encoding )))
 {
 StringBuilder sb = new StringBuilder();
 String line;
 while(( line = br.readLine()) != null ) {
 sb.append( line );
 sb.append( '\n' );
 }
 return sb.toString();
 }
}

• Arsen Alexanyan: May be :) I think he is not looking for the efficient way, he is just trying to learn
• AgilePro: Actually, reading characters can be more efficient that reading lines which are strings, because a to make a String, you have top copy each of the characters in to the String, and that is only to return a String which is then copied to another String....
• Arsen Alexanyan: @Aubin Why it is not efficient?
• AgilePro: The native methods for moving a block of byte or characters can be faster than a loop that handles each character. However, what is more important is to look at whether there is needless extra search, converting, and copying of data, which accounts for more overhead than the character loop overhead. By the way, this answer is putting a byte into a character, which is a problem.
• Arsen Alexanyan: @AgilePro Why it is a problem converting byte into character?

Answer 2

public static String getFileContent(
 FileInputStream fis,
 String encoding ) throws IOException
 {
 try( BufferedReader br =
 new BufferedReader( new InputStreamReader(fis, encoding )))
 {
 StringBuilder sb = new StringBuilder();
 String line;
 while(( line = br.readLine()) != null ) {
 sb.append( line );
 sb.append( '\n' );
 }
 return sb.toString();
 }
}

• Paul Vargas: Depending on the requirements of the Original Poster, perhaps needed the file encoding and line separator (or read as it appears in the file).
• Aubin: Yes, you're right but when reading stream to RAM we may accept the line terminator will be normalized into \n (assumption to debate)
• Puce: The close should happen in a finally block, or better in a try-with-resource block.
• AgilePro: You need to specify the character encoding. You can not assume that the platform default encoding will be correct.
• bhushan23: I'm using file as a parameter to this function and if a condition satisfies then i have to print whole path of a file that's why i took fileinputstream as a parameter....

Answer 3

Using Apache commons IOUtils function

import org.apache.commons.io.IOUtils;
InputStream inStream = new FileInputStream("filename.txt");
String body = IOUtils.toString(inStream, StandardCharsets.UTF_8.name()); 

• Farid: This won't work in all cases as encoding could be different from UTF_8

Answer 4

Don't make the mistake of relying upon or needlessly converting/losing endline characters. Do it character by character. Don't forget to use the proper character encoding to interpres the stream.

public String getFileContent( FileInputStream fis ) {
 StringBuilder sb = new StringBuilder();
 Reader r = new InputStreamReader(fis, "UTF-8"); //or whatever encoding
 int ch = r.read();
 while(ch >= 0) {
 sb.append(ch);
 ch = r.read();
 }
 return sb.toString();
}

If you want to make this a little more efficient, you can use arrays of characters instead, but to be honest, looping over the characters can be still quite fast.

public String getFileContent( FileInputStream fis ) {
 StringBuilder sb = new StringBuilder();
 Reader r = new InputStreamReader(fis, "UTF-8"); //or whatever encoding
 char[] buf = new char[1024];
 int amt = r.read(buf);
 while(amt > 0) {
 sb.append(buf, 0, amt);
 amt = r.read(buf);
 }
 return sb.toString();
}

• AgilePro: Actually, there is good reason to believe it is more efficient than the code that is scanning for, and manipulating, the end of line characters, then copying that into a string for return. Character by character efficiently works with the native content of the stream.
• AgilePro: sorry, forgot the Reader to convert bytes to chars.
• Roger Lindsjö: You can not declare a variable in the while expression part. And the read of a Reader returns int, not char.
• AgilePro: Yes, I actually prefer to keep the declaration out of the block condition, even though it means you have two lines with read statements. I have changed it thus.

Answer 5

From an answer I edited here:

static String convertStreamToString(java.io.InputStream is) {
 if (is == null) {
 return "";
 }
 java.util.Scanner s = new java.util.Scanner(is);
 s.useDelimiter("\\A");
 String streamString = s.hasNext() ? s.next() : "";
 s.close();
 return streamString;
}

This avoids all errors and works well.

Answer 6

Use following code ---->

try {
 FileInputStream fis=new FileInputStream("filename.txt");
 int i=0; 
 while((i = fis.read()) !=-1 ) { // to reach until the laste bytecode -1
 System.out.print((char)i); /* For converting each bytecode into character */ 
 }
 fis.close();
} catch(Exception ex) {
 System.out.println(ex); 
}