File Handling in Java.pdf

https://firstcode.school/file-handling-in-java/

1. FileHandlinginJava
Ingeneralterms,afileisacollectionofinformation.InJava,afileisanabstracttype
thatstoresrelatedinformationtogether.Thisarticlewillletyouknowaboutthefile
anditsvarioususefuloperations.Butbeforegettingtoknowaboutit,youmusthave
aclearideaaboutStreamandFileMethodsinJava.
StandardstreamsinJava:
Astreamisaseriesofdata.IthelpsusperformI/Ooperationswithafile.The
operatingsystemwilldefinethreestandardstreams.TheneedforstandardInput
andOutputusnecessary.Thisiswhereausercantakeinputfromakeyboardand
resultinproducinganoutputonthemonitor.Thoughtheinputandoutputdevices
mayvary,theprocessisthesame.InCandC++,therearethreestandarddevices
STDIN,STDOUTandSTDERR.
Itensuresthatthesestandardstreamsareaccessibleviathemembersofthe
systemclassinJava:
1.StandardInput:Itprovidesinputdatatotheprogram.Thistaskismostly
accomplishedbyakeyboardthatisusedasastandardinputstreamandisdenoted
asSystem.in.
2.StandardOutput:Itprovidestheresultofthedatathatthatprogramproduces.this
outputisusuallydisplayedonthecomputerscreenwhichisthestandardoutput
streamandisdenotedasSystem.out.

2. 3.StandardError:Itdisplaystheerrordatathattheprogramproduces.Thisis
usuallydisplayedonthecomputerscreenthatisusedasthestandarderrorstream
andisrepresentedasSystem.err.
InputStreaminJava:
ThesuperclassofallinputstreamsistheJavaInputStreamclass.Weuseinput
deviceslikethekeyboard,network,etc.,toreadtheinput.ThisInputStreamisalso
anabstractclass.
ThevarioussubclassesoftheInputStreamclassare:
■AudioInputStream
■ByteArrayInputStream
■FileInputStream
■FilterInputStream
■StringBufferUnputStream
■ObjectInputStream
CreatinganInputStreaminjava:
InputStreamobj=newFileInputStream();
S.n
o
Method Description
1 read() Wecanusethistoreadabyteofdatefromtheinputstream.
2
read(byte[]
array)()
Itreadsabytefromthestreamandletsusstorethebyteinthe
mentionedarray.
3 mark() Itmarksthepositionintheinputstreamtillthedataisread.

3. 4 available() Itreturnsthenumberofbytesfromtheinputstream.
5markSupported()Itchecksifthemark()methodandresult()methodinthesystem.
6 reset() Itreturnsthecontroltothepointwherethemarkwasset.
7 skips()
Itskipsandremovesthementionednumberofbytesfromtheinput
stream.
8 close() Itclosestheinputstream.
9 finalize()
Itcleanstheconnectiontothefile.Italsoensuresthattheclose
method
SampleprogramtocreateInputStreamReadertoreadthestandardinputstream
untilthecodewordforquit,‘q’isenteredbytheuser:
importjava.io.*;
publicclassFirstCodeReadConsole {
publicstaticvoidmain(Stringargs[])throwsIOException{
InputStreamReader cin=null;
try{
cin=newInputStreamReader(System.in);
System.out.println("Enterthecharacter'q'toquit.");
charc;
do{
c=(char)cin.read();
System.out.print(c);

4. }while(c!='q');
}finally{
if(cin!=null){
cin.close();
}
}
}
}
Output:
1
2
r
q
q
OutputstreaminJava:
Theoutputstreamgivestheabilitytowritedataintovariousoutputdevices.These
devicesincludethemonitor,printerandevenfile.OutputStreamisanabstract
superclasstorepresenttheoutputstream.
Thevarioussubclassesundertheoutputstreamclassare:
■ByteArrayOutputStream
■FileOutputStream
■StringBufferOutputStream
■DataOutputStream
■PrintStream

5. CreatinganOutputStream:
OutputStreamobj=newFileOutputStream();
S.N
o
Method Description
1 write() Itwritesthespecifiedbytetotheoutputstream.
2
write(byte[]
array)
Itwritesthebyteswhicharegiveninaspecificarraytotheoutput
stream
3 close() Itclosestheoutputstream
4 flush()
Itforcestowriteallthedatapresentinanoutputstreamtoits
destination
5 finalize()
Itcleanstheconnectiontothefile.Itensuresthattheclosemethodifthe
fileoutstreamisinvokedintheabsenceofotherreferencestothe
stream.
OutputStreamsOperationsinJava:
Therearethreemethodstowritethedataintoastream.Thesemethodsare
availableintheIndependentoutputstream.Thesemirrortheread()methods
presentintheInputStreamClass,whichisalsoanabstractclass.
OutputStreamsOperations Description
FileOutputStream Towriteafile

6. ObjecyInputStream Towriteobjectstoastream
ByteArrayOutputStream Towriteanarrayofbytes
PipeOutputStream Towritetoapipedstream
FilterOutputStream Tofiltertheoutputfromanendstream
Basedonthedatatype,thestreamisdividedintotwocategories:
1.ByteStream
2.CharacterStream
ClassificationofI/Ostreamsinjava:
1.ByteStream:
ByteStreamtakesplacewithbytedata.Inthistypeoffilehandlingmethod,thebyte
streamprocessallowsexecutionwithbytedata.
2.CharacterStream:
Ittakesplacewithcharacterdata.Inthistypeoffilehandlingmethod,thecharacter
streamprocessallowsexecutionwithcharacterdata.
JavaFileClassMethods:
S.N
o
Method
Return
Type
Description

7. 1 canRead()Boolean
Usingthismethod,wecancheckifthefilecanbe
readornot.
2createNewFile()BooleanWecanusethismethodtocreateanewfile.
3 canWrite()BooleanItletsuscheckifwecanwriteinthefileornot.
4 exists()Boolean
Itisusedtocheckifthementionedfileisavailable
ornot.
5 delete()Boolean Usingthismethod,wecandeleteafile.
6 getName()String
Wecanusethismethodtofindthenameofthe
file.
7
getAbsolutePath
()
String
Thismethodhelpsusinknowingtheabsolute
pathnameofthefile.
8 length()Long Itletsusattainthesizeofthefilesinbytes
9 list()String[]
Usingthismethod,wecangetthearrayoffilesin
thedirectory
10 mkdir()BooleanWecanusethismethodtocreateanewdirectory
WhatisFilehandlinginJava?
Filehandlingistheprocessofreadingandwritingdataintoafile.TheFileclassin
Javaispresentinthejava.iopackage.Wecansimplyusethefileclassbycreating
anobjectfortheclassandspecifyingthenameofthefileordirectory.

8. WhyisFilehandlingrequired?
Tobeginwith,letusfirstunderstandtheimportanceofthisconcept.
Filehandlingisanintegralpartofeveryprogramminglanguage.Storingtheoutput
ofaprograminafileformatmakesiteasilyretrievable.Therefore,filehandlingisan
essentialpartofprogramming.
JavaFileOperations:
Thevariousoperationsthatwecanperforminafileinjavaarelistedbelow:
■Creatingafile
■Gettingfileinformation
■Writingintoafile
■Readingfromafile
■Deletingafile
1.FilecreationinJava:
TheFileCreationoperationletsuscreateanewfile.Themethodthatperformsthis
actionisthecreateNewFile()method.Itreturnstrueaftersuccessfullycreatinga
newfile.Ifthefieldnamealreadyexists,thismethodreturnsfalse.
SampleprogramtocreateafileinJava:
importjava.io.File;
importjava.IOException;
classFirstCode{
publicstaticvoidmain(Stringargs[]){
try{

9. Filef()=newFile(“D:CreatingFileExample. txt”);
if(f().createNewFile()){
System.out.println(“Thefile”+f().getName()+“iscreatedsuccefully.”);
}else{
System.out.println(“Thefilenamealreadyexistsinthedirectory”);
}
}catch(IOExceptionexception){
System.out.println(“Error!!!”);
exception.printStackTrace();
}
}
}
2.Readfromafile/GetFileInformation:
Weperformthisoperationtoretrievethedatafromthefile.Someofthemethods
thatletusachievethisarename,absolutepath,isreadable,iswriteableandlength.
Sampleprogramtoreadinformationfromafile:
importjava.io.File;
classFirstCode{
publicstaticvoidmain(Stringargs[]){
Filef()=newFile(“D:ReadingFileExample. txt”);
if(f().exists()){
System.out.println(“Thefilenameis:”+f()getName());//togetfilename

10. System.out.println(“Theabsolutepathis:”+f().getAbsolutepath());//togetfile
path
//tocheckitthefileiswriteableornot
System.out.println(“Isthefilewriteable?”+f().canWrite());
//tocheckifthefileisreadableornot
System.out.println(“Isthefilereadable?”+f().canRead());
//togetthelengthofthefile
System.out.println(“Thesizeofthefileinbytesis:”+f().length());
}else{
System.out.println(“Thefiledoesnotexist”);
}
}
}
3.Writeintoafile:
Towriteintoafile,weusetheFileWriterclassandthewrite()method.Thestream
shouldbeclosedusingtheclose()methodtoretrievetheresources.
Sampleprogramtowriteintoafile:
importjava.io.FileWriter;
importjava.io.IOException;
classFirstCode{
publicstaticvoidmain(Stringargs[]){
try{

11. FileWriterfwrite=newFileWriter(“D:FileWritingExample. txt”);
fwrite.write(“LearnJavawithFirstCode”);
fwrite.close();
System.out.println(“Contentissuccessfullywritteninthefile”);
}
catch(IOExceptione){
System.out.println(“Error!!!”);
e.printStackTerrace();
}
}
}
JavaFileWriter:
ThisclassinJavahelpstheprogrammerstocreatenewfilewritingcharacters.It
inheritsfromtheOutputStreamclass.
Theconstructorspresentinthisclassgenerallyassumethatthebyte-buffersizeand
defaultcharacterencodingareacceptable.Todeclaretheseconstructors,wemust
constructOutputStreamWriteronaFileOutputStream.
TheJavaFileWriterisverymuchusefulforwritingstreamsof
characters.constructors
4.Readfromafileinjava:
Toreadthecontentpresentinthefile,weneedtousetheScannerclass.The
streamisclosedusingtheclose()method.WecancreateanobjectfortheScanner

12. classtoimplementthehasNextLine()andnextLine()methods.Thesemethods
retrievetheinformationfromthefile.
JavaFileReader:
TheFileReaderinJavaplaysavitalroleinreadingthedatathatispresentinthe
formofcharacters.Thisisdoneintheformofa‘text’file.TheFileReaderinherits
fromtheInputStreamReaderclass.
Theconstructorsinthisclassassumethedefaultcharacterencodingandthedefault
byteareappropriate.AstheJavaFileReaderisusedonlyforparticularlyreading
streamsofcharacter,youcanusetheFileInputStreamtoreadstreamsofrawbytes.
Methods:
Methods Description
publicintread()throws
IOException
Thismethodreadasinglecharacterandblocksoneuntil
anotheroneisavailable.Thatis,aninput/outputerror
occurs.
publicintread(char[]cbuff[])
throwsIOException
Itreadscharactersintoanarrayandblocksuntila
characterisavailable.
publicabstractintread(char[]
buff,intoff,intlen)whichthrows
anIOException
Itreadcharactersintoaportionofanarray.Itblocksuntil
theinputisavailableoranerroroccursintheinputand
output,ortheendofthestreamisreached.
Parameters:
■cbuff–Destinationbuffer.
■off–Itsetstheoffsetatwhichtostartstoringcharacters.
■len–itusestoseethemaximumnumberofcharacterstoread.

13. ■publiclongskip(longn)throwsIOException:Itskipsthecharactersand
blocksuntilsomecharactersareavailable,anI/Oerroroccursorthe
streamendisreached.
Sampleprogramtoreadfromafile:
importjava.io.File;
importjava.io.FileNotFoundException ;
importjava.util.Scanner;
classFirstCode{
publicstaticvoidmain(Stringargs[]){
try{
Filef=newFile(“D:ReadFromFile.txt”);
Scanners=newScanner(f);
while(s.hasNextLine()){
StringfileData=s.nextLine();
System.out.println(fileData);
}
s.close();
}catch(FileNotFoundException exception){
System.out.println(“Error!!!”);
exception.printStackTrace();
}
}
}

14. Deletingafile:
Knowingtodeleteafileisasimportantascreatingone.Thedelete()method
performsthistask.Weneednotclosethestreamwiththeclose()methodorusethe
FileWriterandScannerclasshere.
Sampleprogramtodeleteafile:
importjava.io.File;
classFirstCode{
publicstaticvoidmain(Stringargs[]){
Filef()=newFile(“D:DeletingFile.txt”);
if(f().delete()){
System.out.println(f().getname()+“Thefileisdeleted”);
}else{
System.out.println(“Error!!!”);
}
}
}
JavaDirectories:
Methodstocreateandmodifyfilesanddirectoriesin
java:
Methods Description

15. renameTo(File
path)
Thefilethatthecurrentobjectrepresentswillberenamedtothepaththat
thefileobjectpassesasanargumenttothemethod.
setreadonly()
Itsetsthefilesthatrepresentthecurrentobjectasread-onlyandreturns
truewhenthetaskissucceeded.
mkdir() Itcreatesadirectorywiththepathspecifiedbythecurrentfileobject.
mkdirs()
Createsthedirectoryrepresentedbythecurrentfileobject,including
parentdirectoriesthatarerequired.
createanewfile()
Itcreatesanewemptyfilewithapathnamedefinedbythecurrentfile
objectaslongasthefileexists.
delete()
Thisdeletesthefileinadirectoryrepresentedbythecurrentfileobjectand
returnstrueifthedeleteissuccessful.
createDirectory(Path,FileAttribute</>)
CreatingDirectoriesinjava:
JavaprovidesacoupleofbeneficialFileutilitymethodsthatareusedtocreate
directories.
■Themkdir()methodcreatesadirectory.Itreturnstrueforsuccessand
falseforfailure.Thefailuredenotesthatthepaththatismentionedinthe
Fileobjectexistsalready.Italsodenotesthatthedirectorycannotbe
createdifthepathdoesnotexist.
■Themkdirs()methodscreatebothadirectoryandalsoparentsofthe
directory.
Sampleprogramtocreateadirectory:
importjava.io.File;

16. publicclassCreateDirFirstCode{
publicstaticvoidmain(Stringargs[]){
Stringdirname="/tmp/user/java/bin" ;
Filed=newFile(dirname);
d.mkdirs();
}
}
ListingdirectoriesinJava
TheFileobjectprovidesthelist()methodtolistdownallthefilesanddirectoriesthat
arepresent.
Sampleprogramtolistthedirectories:
importjava.io.File;
publicclassReadDirFirstCode {
publicstaticvoidmain(String[]args){
Filefile=null;
String[]paths;
try{
file=newFile("/tmp");
paths=file.list();
for(Stringpath:paths){
System.out.println(path);
}

17. }catch(Exceptione){
e.printStackTrace();
}
}
}
Output:
test1.txttest2.txt
ReadDir.java
ReadDir.class
QueryingFilesandDirectoriesinJava:
Method Description
exists()
Itreturnsifthefileordirectoryreferredtobythefileobjectexistsandfalse
otherwise
isfile() Itreturnsifthefileobjectreferstoanexistingfileandfalseotherwise.
canread()Itreturnstrueifitallowsreadingthesilethatisreferredbythefileobject.
canwrite(
)
Itreturnstrueifyouarepermittedtowritethefilereferredbythefileobject.
Constructors:

18. Constructors Description
FileWriter(Filefile)
ThisconstructorconstructsaFileWriterobject
whenafileobjectisgiven.
FileWriter(Filefile,booleanappend)ItconstructsanobjectforFilewriter.
FileWriter(FileDescriptorfd)
ConstructsaFileWriterobjectassociatedusing
afiledescriptor.
FileWriter(StringfileName)
ItconstructsaFileWriterobjectwhenafile
nameisgiven.
publicvoidwrite(intc)throwsIOExceptionItwritesasinglecharacter.
publicvoidwrite(char[]stir)throws
IOException
Itwritesanarrayofcharacter.
publicvoidwrite(Stringstr)throws
IOException
ItwritesastringinJava.
FileWriter(Stringfilename,Booleanappend)
ItconstructsaFileWriterobjectwhenafile
nameispresent.
publicvoidwrite(Stringstr,intoff,intlen)
throwsIOException
ItwritesaportionofaString.
Conclusion:
Thisarticlewouldhavehelpedyouinknowingvariousdetailsaboutfilehandlingin
Java.Youcannowcreateyourownfileandperformvariousfilehandlingoperations
toit.Thisletsyoustorethedataandretrievethemeasily.