We know that Buffered reader and writers read and write data in big chunks
Byte Streams can be used to read int,char and String as well. The only thing is data is in bytes so we don't have to parse it i.e we don't have to do anything like this
int loc = Integer.parseInt(data[0]);
int destination = Integer.parseInt(data[2]);
The reason is byte stream can be used to read and write any of the primitive data types like int double etc and even String even though String is not a primitive data type. And instead of FileReader and FileWriter we use FileInputStream and FileOutputStream
But byte streams reads and writes raw bytes ,one byte at a time data is buffered using BufferedInputStream and BufferedOutputStream
FileInput streams use methods like readInt,readUtf etc to read integers,Strings etc same as writeInt,writeUtf
And since these file input streams deal with binary files so we better create a .dat file and not a .txt file as data is not entirely human readable in this file
Reading data from dat file is easier than reading from text file as we don't have to do any String parsing to get the integer value.
Data input streams take care of building primitive types like int ,double from the bytes in the file
Another inp thing to note is we need to need the format of file we want to read before using byte streams to read data i.e if first letter is a digit then a String then digit etc.Now this is easy if we want to read text file using byte stream as we can open and read the file as it is in human readable form. But it becomes tricky it file is a dat file as in our case below. So in that case either we are creating that file ourself otherwise we wont know
the format in which various data types appeared in that file ,so reading data becomes very tricky.
For example below we know the format while writing data is
locfile.writeInt(location.getLocationId());
locfile.writeUTF(location.getDescription());
Then we read data in the same format as well.
int locId = locfile.readInt();
String description = locfile.readUTF();
The full code is below
public static void main(String[] args) throws IOException {
try(DataOutputStream locfile = new DataOutputStream(new BufferedOutputStream(new FileOutputStream("locations.dat")));)
{
//here location is a user defined class and lacations is map of class objects as values
for(location location:locations.values()){
// writeInt used to write Int values similarly we have methods to write other java primitive types lik writeLong ,writeDouble etc
locfile.writeInt(location.getLocationId());
// writeUTF used to write text data
locfile.writeUTF(location.getDescription());
}
}
public static void readData(String[] args) throws IOException {
try (DataInputStream locfile = new DataInputStream(new BufferedInputStream(new FileInputStream("locations.dat")))) {
boolean endOfFile = false;
while(!endOfFile) {
try {
Map exits = new LinkedHashMap<>();
int locId = locfile.readInt();
String description = locfile.readUTF();
System.out.println("Loc id : " + locId + " description id :"+description);
}
}
//This catch is used to end the while loop
// i.e when we reach end of file set endOfFile = true
// so that while loops after that*//*
catch (EOFException e){
endOfFile = true;
}
}
}
//*If there is any other exception other than eof , i.e any exception
// thrown by try with resources it will be catch by the below catch block*//*
catch (IOException e) {
e.printStackTrace();
}
}