[Java] various methods for reading and writing files and small examples

1. Use filewriter and filereader to read and write files

Import Java. io. *; <br/> public class javaapplication2 {</P> <p>/** <br/> * @ Param ARGs the command line arguments <br/> */<br/> public static void main (string [] ARGs) throws filenotfoundexception, ioexception {</P> <p> filewriter fw = new filewriter ("test.txt"); <br/> FW. write ("dddd"); // just do this .. it will automatically convert to its unicode encoding .. or FW. write (INT) C); force conversion. <br/> FW. append ("wwwwww"); <br/> FW. flush (); <br/> FW. close ( ); </P> <p> filereader Fr = new filereader ("test.txt"); <br/> int CH = 0; <br/> while (CH = Fr. read ())! =-1) <br/>{< br/> system. Out. Print (char) CH); <br/>}< br/>}Ii. Examples of Multiple File Reading Methods

1. Read File Content by byte
2. Read File Content by character
3. Read File Content by row
4. Randomly Read File Content

<Br/> package readfile; <br/> Import Java. io. bufferedreader; <br/> Import Java. io. file; <br/> Import Java. io. fileinputstream; <br/> Import Java. io. filereader; <br/> Import Java. io. ioexception; <br/> Import Java. io. inputstream; <br/> Import Java. io. inputstreamreader; <br/> Import Java. io. randomaccessfile; <br/> Import Java. io. reader; <br/> public class readfromfile {<br/>/** <br/> * reads files in bytes. It is often used to read binary files, slices, sounds, Images and other files. <Br/> * @ Param filename file name <br/> */<br/> Public static void readfilebybytes (string filename) {<br/> file = new file (filename); <br/> inputstream in = NULL; <br/> try {<br/> system. out. println ("Read File Content in bytes, one byte at a time :"); <br/> // read one byte at a time <br/> In = new fileinputstream (File); <br/> int tempbyte; <br/> while (tempbyte = in. read ())! =-1) {<br/> system. out. write (tempbyte); <br/>}< br/> in. close (); <br/>}catch (ioexception e) {<br/> E. printstacktrace (); <br/> return; <br/>}< br/> try {<br/> system. out. println ("Read File Content in bytes, read multiple bytes at a time :"); <br/> // read multiple bytes at a time <br/> byte [] tempbytes = new byte [100]; <br/> int byteread = 0; <br/> In = new fileinputstream (filename); <br/> readfromfile. showavailablebytes (in); <br/> // read multiple bytes into the byte array. Read is the number of bytes read at a time <br/> while (byteread = in. Read (tempbytes ))! =-1) {<br/> system. out. write (tempbytes, 0, byteread); <br/>}< br/>} catch (exception E1) {<br/> e1.printstacktrace (); <br/>} finally {<br/> If (in! = NULL) {<br/> try {<br/> in. close (); <br/>} catch (ioexception E1) {<br/>}< br/>/** <br/> * reads a file in characters, commonly used for reading text, numbers, and other types of files <br/> * @ Param filename file name <br/> */<br/> Public static void readfilebychars (string filename) {<br/> file = new file (filename); <br/> reader = NULL; <br/> try {<br/> system. out. println ("Read File Content in characters, one byte at a time:"); <br/> // read one character at a time <br/> reader = N EW inputstreamreader (New fileinputstream (File); <br/> int tempchar; <br/> while (tempchar = reader. Read ())! =-1) {<br/> // for Windows, when the RN characters are together, a line break is displayed. <Br/> // if the two characters are displayed separately, the rows are changed twice. <Br/> // Therefore, block R or N. Otherwise, there will be a lot more blank lines. <Br/> If (char) tempchar )! = 'R') {<br/> system. out. print (char) tempchar); <br/>}< br/> reader. close (); <br/>}catch (exception e) {<br/> E. printstacktrace (); <br/>}< br/> try {<br/> system. out. println ("Read File Content in characters, multiple bytes read at a time :"); <br/> // read multiple characters at a time <br/> char [] tempchars = new char [30]; <br/> int charread = 0; <br/> reader = new inputstreamreader (New fileinputstream (filename); <br/> // read multiple characters into the character array, charread is the number of characters read at a time <B R/> while (charread = reader. Read (tempchars ))! =-1) {<br/> // If (charread = tempchars. length) & (tempchars [tempchars. length-1]! = 'R') {<br/> system. out. print (tempchars); <br/>}else {<br/> for (INT I = 0; I <charread; I ++) {<br/> If (tempchars [I] = 'R') {<br/> continue; <br/>}< br/> else {<br/> system. out. print (tempchars [I]); <br/>}< br/>} catch (exception E1) {<br/> e1.printstacktrace (); <br/>}finally {<br/> If (reader! = NULL) {<br/> try {<br/> reader. close (); <br/>} catch (ioexception E1) {<br/>}< br/>/** <br/> * read files in behavior units, commonly used to read row-oriented formatted files <br/> * @ Param filename file name <br/> */<br/> Public static void readfilebylines (string filename) {<br/> file = new file (filename); <br/> bufferedreader reader = NULL; <br/> try {<br/> system. out. println ("read the file content in the unit of action, one whole row at a time:"); <br/> reader = new bufferedreade R (New filereader (File); <br/> string tempstring = NULL; <br/> int line = 1; <br/> // read a row at a time, until the end of reading null is the file <br/> while (tempstring = reader. readline ())! = NULL) {<br/> // display the row number <br/> system. out. println ("line" + LINE + ":" + tempstring); <br/> line ++; <br/>}< br/> reader. close (); <br/>}catch (ioexception e) {<br/> E. printstacktrace (); <br/>}finally {<br/> If (reader! = NULL) {<br/> try {<br/> reader. close (); <br/>} catch (ioexception E1) {<br/>}< br/>/** <br/> * Randomly Read File content <br/> * @ Param filename file name <br/> */<br/> Public static void readfilebyrandomaccess (string filename) {<br/> randomaccessfile randomfile = NULL; <br/> try {<br/> system. out. println ("randomly read a file:"); <br/> // open a random access file stream in read-only mode <br/> randomfile = new randomaccessfile (filenam E, "R"); <br/> // file length, number of bytes <br/> long filelength = randomfile. length (); <br/> // start position of the file to be read <br/> int beginindex = (filelength> 4 )? 4: 0; <br/> // move the start position of the read file to the beginindex position. <Br/> randomfile. seek (beginindex); <br/> byte [] bytes = new byte [10]; <br/> int byteread = 0; <br/> // read 10 bytes at a time. If the file content is less than 10 bytes, read the remaining bytes. <Br/> // assign the number of bytes read at a time to byteread <br/> while (byteread = randomfile. Read (bytes ))! =-1) {<br/> system. out. write (bytes, 0, byteread); <br/>}< br/>} catch (ioexception e) {<br/> E. printstacktrace (); <br/>}finally {<br/> If (randomfile! = NULL) {<br/> try {<br/> randomfile. close (); <br/>} catch (ioexception E1) {<br/>}< br/>/** <br/> * display the remaining bytes in the input stream count <br/> * @ Param in <br/> */<br/> Private Static void showavailablebytes (inputstream in) {<br/> try {<br/> system. out. println ("number of bytes in the Current byte input stream:" + in. available (); <br/>} catch (ioexception e) {<br/> E. printstacktrace (); <br/>}< br/> Public static void main (string [] ARGs) {<br/> string filename = "D: /t.txt "; <br/> readfromfile. readfilebybytes (filename); <br/> readfromfile. readfilebychars (filename); <br/> readfromfile. readfilebylines (filename); <br/> readfromfile. readfilebyrandomaccess (filename); <br/>}< br/>