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[Java教程]Java中的文件输入输出流


最近学习了如何读取输出文件,贴上部分代码:

TestInputStream1():

String strFile = "Data/DataGroup.cpp";

File = new File(strFile);

InputStream in = null; 

in = new FileInputStream(file);

//创建合适文件大小的数组,一次性把数据从文件中读出

b1 = new byte[(int)file.length()];

// 读取文件中的内容到b[]数组,如果read()返回读取的字节内容,

// 当内容为空时返回-1,可以以此作为判断文件内容是否读取完毕        

in.read(b1);       

in.close();

textArea.append(new String(b1));

 

TestInputStream2():

int iSize = 1024;

boolean blSleep = true;

String strFile = "Data/DataGroup.cpp";

File file = new File(strFile);

int iCount = (int)file.length()/iSize;

InputStream in = null;     

in = new FileInputStream(file);        

b2 =new byte[iSize];

int temp = 0;

int no = 0;

while((temp = in.read()) != -1){

                                     no++;

                                     in.read(b2);                        

                                     System.out.println(new String(b2));                                   

                                     if(no < iCount){

                                               in.read(b2);

                                               System.out.println(new String(b2));

                                     }

                                     else{

                                               blSleep = false;

                                               System.out.print((char)temp);

                                     }

                            }

in.close();

 

 

 

 

 

 

执行TestInputStream1(),后:

TestOutputStream():读文本文件,然后显示到组件,写到另外一个文件)

// 写文件时的相关变量

String strOut = "*Data/DataGroup_copy.cpp";

File file = new File(strOut);

OutputStream output = null;

output = new FileOutputStream(file);

output.write(b1);

output.close();

 

TestPrintStream()://读取并输出屏幕上,输出到文件上

String strFile = "Data/DataGroup.cpp";

File file = new File(strFile);

InputStream in = null;     

in = new FileInputStream(file);

//创建合适文件大小的数组,一次性把数据从文件中读出

b1 = new byte[(int)file.length()];              

// 读取文件中的内容到b[]数组,如果read()返回读取的字节内容,

// 当内容为空时返回-1,可以以此作为判断文件内容是否读取完毕        

in.read(b1);       

in.close();

               

// 将数据输出到屏幕

PrintStream printStream = new PrintStream(System.out);

printStream.println(new String(b1));

printStream.flush();    // 彻底完成输出并清空缓冲区

printStream.close();

       

// 将数据输出到文件

File filePrint = new File("Data/print.cpp");

printStream = new PrintStream(filePrint);

printStream.println(new String(b1));

printStream.close();   

 

 

 

 

 

 

 

 

 

 

 

TestDataInputStream()

// 键盘输入(如何自适应根据用户输入的数据多少分配空间)

byte b[] = new byte[12];

DataInputStream dataInputStream = new DataInputStream(System.in);

String str = null;

dataInputStream.read(b);

dataInputStream.close();

System.out.println(new String(b));

       

// 文件输入

String strFile = "Data/表2-5.txt";     

byte byFile[] = null;

File file = new File(strFile);

InputStream instream = null;       

instream = new FileInputStream(file);

dataInputStream = new DataInputStream(instream);       

float temp = (float) 0.0;

str = null;

byFile = new byte[(int)file.length()];

dataInputStream.read(byFile);

dataInputStream.close();       

System.out.println(new String(byFile));

 

TestDataInputStream2()//二进制

System.out.println("从文件中每次读取一个数值");

DataInputStream dataInputStream = null;        

       

// 文件输入     

String strFile = "Data/表2-5_Copy.txt";    

File file = new File(strFile);

InputStream instream = null;       

instream = new FileInputStream(file);

   

dataInputStream = new DataInputStream(instream);       

       

System.out.println("二进制文件读取结果的输出!");

float temp = (float) 0.0;          

// 判断是否文件结束

while(dataInputStream.available() > 0){

    temp = dataInputStream.readFloat();

    System.out.println(temp);

           

instream.close();

    dataInputStream.close();

TestDataOutputStream()

DataOutputStream outputStream = null;

DataInputStream inputStream = null;

// 文件输入

byte byFile[] = null;

File file = new File("Data/表2-5.txt");

InputStream instream = null;       

instream = new FileInputStream(file);

inputStream = new DataInputStream(instream);       

String str = null;

byFile = new byte[(int)file.length()];

inputStream.read(byFile);

str = new String(byFile);          

inputStream.close();

String strSplit[] = str.split(" ");

System.out.println(strSplit.length);

// 把字符串str中的数据一个一个写入文件中(二进制格式文件)

String strFile = "Data/表2-5_Copy.txt";

file = new File(strFile);

OutputStream out = null;

out = new FileOutputStream(file);

outputStream = new DataOutputStream(out);          

        for(int i = 0;i < strSplit.length;i++){

            float temp = Float.valueOf(strSplit[i]);

            System.out.println(temp);

            outputStream.writeFloat(temp);

        }

            out.close();

            outputStream.close();  

    }

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TestBufferReaderAndBufferedWriter()

// 键盘输入 

InputStreamReader isr = new InputStreamReader(System.in);

BufferedReader br = new BufferedReader(isr) ;

String str = null;

str = br.readLine();

isr.close();

br.close();

System.out.println(str);

// 读文件

str = null;

String strFile = "Data/result_表2-5.txt";

       

if(isr != null)             isr = null;        

isr = new InputStreamReader(new FileInputStream(new File(strFile)));

br = new BufferedReader(isr);          

// 写文件

String strWrite = "Data/result_表2-5_copy.txt";

OutputStreamWriter out = null;

BufferedWriter bw = null;

       

out = new OutputStreamWriter(new FileOutputStream(new File(strWrite)));

bw = new BufferedWriter(out);  

 

// Java中有没有类似于rewind函数,即对指针进行重定位?????????

isr = new InputStreamReader(new FileInputStream(new File(strFile)));

br = new BufferedReader(isr);  

str = null;

   

while((str = br.readLine()) != null){

    System.out.println(str);

    bw.write(str);  // 在使用readLine读取时,换行符已经被取消

    bw.newLine();

}          

bw.close();

out.close();