Download - 08 Luồng vào ra trong java

7/31/2019 08 Lung vo ra trong java

1/45

Cc lung vo / ra


2/45

Cc lung vo ra 2Nguyn Vit H

Ni dung

Khi nim v lung d liu Lung v tp

Lp File

Truy cp tp tun t Truy cp tp ngu nhin


3/45


Ti liu tham kho

Thinking in Java, chapter 12 Java how to program, chapter 17


4/45


Lung d liu (data streams)

Chng trnh Java nhn v gi d liuthng qua cc i tng l cc thc ththuc mt kiu lung d liu no

Lung (stream) l mt dng d liu n tmt ngun (source) hoc i n mt ch(sink)

Ngun v ch c th l tp (file), b nh,mt tin trnh (process), hay thit b (bnphm, mn hnh, )


5/45


Lung byte v char

Lung byte: thao tc theo n v byte InputStream

OutputStream

Lung char: thao tc vi k tReader

Writer


6/45


InputStream

int read()

int read(byte buf[])

int read(byte buf[], int

offset, int length)

void close()


7/45


OutputStream

int write(int c)

int write(byte buf[])

int write(byte buf[], int

offset, int length)

void close()

void flush()


8/45


Reader

int read()

int read(char buf[])

int read(char buf[], int

offset, int length) void close()


9/45


Writer

int write(int c)

int write(char buf[])

int write(char buf[], int

offset, int length) void close()

void flush()


10/45


11/45


Ph h ca OutputStream


12/45


Ph h ca Reader


13/45


Ph h ca Writer


14/45


i tng vo / ra

nhp hoc xut d liu, chng ta phito ra i tng vo hoc ra

i tng vo hoc ra thuc kiu lung

tng ng v phi c gn vi mtngun d liu hoc mt ch tiu th dliu


15/45


S dng b m

B m l mt k thut tng tnh hiu qu ca thao

tc vo / ra c v ghi d liu theo khi gim s ln thao tc vi thit b

Thay v ghi trc tip ti thit b th chng trnh ghi ln

bm khi bm y th d liu c ghi ra thit b theo khi c th ghi vo thi im bt k bng phng thc flush()

Thay v c trc tip t thit b th chng trnh c tbm khi bm rng th d liu c c theo khi t thit b


16/45


Nhp xut qua thit b chunConsole I/O

System.out cho php in ra lung ra chun l i tng ca lp PrintStream

System.err cho php in ra lung thng bo

li chun l i tng ca lp PrintStream

System.in cho php c vo t thit b vochun l i tng ca lp InputStream


17/45


18/45


V d:InputStreamReader reader = new InputStreamReader(System.in);

BufferedReader in = new BufferedReader(reader);---

String s;

try {s = in.readLine();

}

catch (IOException e) {...}


19/45


Lp File

Mt trong cc ngun v ch d liu thngthng l tp

Lp File cung cp cc chc nng c bn

thao tc vi tpnm trong gi java.io

to tp, m tp, cc thng tin v tp v th

mc


20/45


To i tng File

File myFile;

myFile = new File(data.txt);

myFile = new File(myDocs, data.txt);

Th mc cng c coi nh l mt tpFile myDir = new File(myDocs);

File myFile = new File(myDir, data.txt);

c phng thc ring thao tc vi th mc


21/45


Cc phng thc Tn tp

String getName()

String getPath()

String getAbsolutePath()

String getParent()

boolean renameTo(File newName)

Kim tra tpboolean exists()

boolean canWrite()

boolean canRead()

boolean isFile()boolean isDirectory()

boolean isAbsolute()


22/45


23/45


Thao tc vi tp k t

c t tpFileReader: c k t t tp

BufferedReader: c c bm (c tng

dng readLine()) Ghi ra tpFileWriter: ghi k t ra tp

PrintWriter: ghi theo dng (print() v println())


24/45


V d:c vo t tpFile file = new File(data.txt);

FileReader reader = new FileReader(file);BufferedReader in = new BufferedReader(reader);

String s;

try {

s = in.readLine();}

catch (IOException e) {

}


25/45


V d:c vo (cont.)File file = new File(data.txt);

FileReader reader = new FileReader(file);

BufferedReader in = new BufferedReader(reader);Abc abc = new Abc();

abc.read(in);

abc.doSomething();


26/45


V d:c vo (cont.)class Abc {

public void read(BufferedReader in) {

String s;try {

s = in.readLine();

...

}catch (IOException e) {}

}

public void doSomething() {...}

...}


27/45


28/45


V d: Ghi ra (cont.)class Abc {

...public void write(PrintStream out) {

...

try {

out.println(s);

out.close();

}

catch (IOException e) {...}

}

}


29/45


V d: Ghi ra (cont.)class Abc {

...public String write() {

String buf;

buf += ...

return buf;

}

}


30/45


V d: File copyimport java.io.*;

public class CopyFile {

public static void main(String args[]) {

try {

FileReader src = new FileReader(args[0]);

BufferedReader in = new BufferedReader(src);

FileWriter des = new FileWriter(args[1]);

PrintWriter out = new PrintWriter(des);

String s;

s = in.readLine();

while (s != null) {out.println(s);

s = in.readLine();

}

in.close();

out.close();

}catch (IOException e) {

e.printStackTrace();

}

}

}


31/45


32/45


Thao tc vi tp d liu (tun t)

c d liu FileInputStream: c d liu t tp

DataInputStream: c d liu kiu nguyn thy

ObjectInputStream: c i tng

Ghi d liu FileOutputStream: ghi d liu ra tp

DataOutputStream: ghi d liu kiu nguyn thy

ObjectOutputStream: ghi i tng


33/45


34/45


Ghi d liu nguyn thy (tun t)import java.io.*;

public class TestDataOutputStream {

public static void main(String args[]) {int a[] = {2, 3, 5, 7, 11};

try {

FileOutputStream fout = new FileOutputStream(args[0]);

DataOutputStream dout = new DataOutputStream(fout);

for (int i=0; i


35/45


c d liu nguyn thy (tun t)import java.io.*;

public class TestDataInputStream {


try {

FileInputStream fin = new FileInputStream(args[0]);

DataInputStream din = new DataInputStream(fin);

while (true) {System.out.println(din.readInt());

}

}

catch (EOFException e) {

}

catch (IOException e) {e.printStackTrace();

}

}

}


36/45


i tng tun t

Mt i tng c th c lu trong bnh ti nhiu vng nh khc nhaucc thuc tnh khng phi l kiu nguyn thy

i tng mun ghi / c c phi thuclp c ci t giao din Serializabley l giao din nhn, khng c phng thc


37/45


import java.io.Serializable;

class Recordimplements Serializable {

private String name;

private float score;

public Record(String s, float sc) {

name = s;

score = sc;}

public String toString() {

return "Name: " + name + ", score: " + score;

}}


38/45


39/45


import java.io.*;

public class TestObjectInputStream {public static void main(String args[]) {

Record r;

try {

FileInputStream fin = new FileInputStream(args[0]);

ObjectInputStream in = new ObjectInputStream(fin);

while (true) {

r = (Record) in.readObject();

System.out.println(r);

}

}

catch (EOFException e) {

System.out.println("No more records");

}

catch (ClassNotFoundException e) {

System.out.println("Unable to create object");

}

catch (IOException e) {e.printStackTrace();

}

}

}


40/45


Lp RandomAccessFile

L mt lp c lp (k tha trc tip tObject)

m nhn vic c v ghi d liu ngu

nhinci t cc giao din DataInput v DataOutput

Kch thc bn ghi phi cnh


41/45


import java.io.*;

public class WriteRandomFile {


int a[] = { 2, 3, 5, 7, 11, 13 };

try {

File fout = new File(args[0]);RandomAccessFile out;

out = new RandomAccessFile(fout, "rw");

for (int i=0; i


42/45


import java.io.*;

public class ReadRandomFile {


try {

File fin = new File(args[0]);RandomAccessFile in = new RandomAccessFile(fin, "r");

int recordNum = (int) (in.length() / 4);

for (int i=recordNum-1; i>=0; i--) {

in.seek(i*4);

System.out.println(in.readInt());}

}

catch (IOException e) {

e.printStackTrace();

}}

}


43/45


Lp Scanner

L lp mi h tr nhp d liu, k thatrc tip t Object (t Java 1.5)

Khi to vi i s l i tng vo

(lung, tp, xu k t) C cc phng thc h tr nhp trc tipnextType, hasNextType


44/45


Scanner sc = new Scanner(System.in);int i = sc.nextInt();

---

Scanner sc;

sc = new Scanner(new File("myNumbers"));

while (sc.hasNextLong()) {

long aLong = sc.nextLong();

}

--

String str = 2 3 5 7;

Scanner sc = new Scanner(str);

while (sc.hasNextInt()) {

System.out.println(sc.nextInt());

}


45/45


class Abc {

public void read(Scanner sc) {

...}

public void doSomething() {...}

...

}

Download - 08 Luồng vào ra trong java

Top Related