Java读写文化总结

Posted 2020-07-18 龍清扬

Java读文件

package 天才白痴梦;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.RandomAccessFile;
import java.io.Reader;

public class JavaIO {
    
    /**
     * 采用的是操作系统底层默认的编码方式，GBK等，非UTF8
     * */
    
    /**
     * 以字节为单位读取文件内容，常用于读取二进制文件，比如图片、影像、声音等文件
     * */
    public static void readFileByBytes(String filename) {
        File file=new File(filename);
        FileInputStream in=null;
        try {
            System.out.println("以字节为单位读取文件,一次读一个字节: ");
            in=new FileInputStream(file);
            int temp=0;
            while ((temp=in.read()) != -1) {
                System.out.println(temp);
            }
            in.close();
        } catch (IOException e) {
            e.printStackTrace();
            return ;
        }
        try {
            System.out.println("以字节为单位读取文件，一次读多个字节： ");
            byte[] temp=new byte[100];
            int byteread=0;
            in=new FileInputStream(file);
            JavaIO.showAvailableBytes(in);
            while ((byteread=in.read(temp)) != -1) {
                System.out.write(temp,0,byteread);
            }
        } catch (Exception e1) {
            e1.printStackTrace();
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e1) {
                    
                }
            }
        }
    }
    /**
     * 以字符为单位读取文件，常用于读文本，数字等类型的文件
     * */
    public static void readFileByChar(String filename) {
        File file=new File(filename);
        Reader reader=null;
        try {
            System.out.println("以字符为单位读取文件内容，一次一个字节：");
            //InputStreamReader类:是字节向字符转换的桥梁
            reader=new InputStreamReader(new FileInputStream(file));
            int temp;
            while ((temp=reader.read()) != -1) {
                if (((char)temp) != ‘\r‘) {
                    System.out.println((char)temp);
                }
            } 
            reader.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            System.out.println("以字符为单位读取文件内容，一次读多个字节： ");
            char[] temp=new char[30];
            int charread=0;
            reader=new InputStreamReader(new FileInputStream(filename));
            while ((charread=reader.read(temp)) != -1) {
                if ((charread == temp.length) && (temp[temp.length-1]!=‘\r‘)) {
                    System.out.println(temp);
                } else {
                    for (int i=0; i<charread; i++) {
                        if (temp[i] == ‘\r‘) {
                            break;
                        } else {
                            System.out.println(temp[i]);
                        }
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    
                }
            }
        }
    }
    /**
     * 以行为单位读取文件，常用于读面向行的格式化文件
     * */
    public static void readFileByLine(String filename) {
        File file=new File(filename);
        BufferedReader reader=null;
        try {
            System.out.println("以行为单位读取文件内容，一次读一整行： ");
            reader=new BufferedReader(new FileReader(file));
            String temp=null;
            int line=1;
            while ((temp=reader.readLine()) != null) {
                System.out.println("line " + line + ": " + temp);
                line++;
            }
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    
                }
            }
        }
    }
    /**
     * 随机读取文件内容
     * */
    public static void readFileByRandomAccess(String filename) {
        RandomAccessFile randomfile=null;
        try {
            System.out.println("随机读取一段文件内容");
            randomfile=new RandomAccessFile(filename,"r");
            long fileLength=randomfile.length();
            int beginIndex=(fileLength > 4 ? 4 : 0);
            randomfile.seek(beginIndex);
            byte[] bytes=new byte[10];
            int byteread=0;
            while ((byteread=randomfile.read(bytes)) != -1) {
                System.out.write(bytes,0,byteread);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (randomfile != null) {
                try {
                    randomfile.close();
                } catch (IOException e) {
                    
                }
            }
        }
    }
    private static void showAvailableBytes(InputStream in) {
        try {
            System.out.println("当前字节输入流中的字节数为：" + in.available());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) {
        String filename="E:\\BaiYiShaoNian.txt";
        JavaIO.readFileByBytes(filename);
        JavaIO.readFileByChar(filename);
        JavaIO.readFileByLine(filename);
        JavaIO.readFileByRandomAccess(filename);
    }
}

Java写文件

package 天才白痴梦;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.OutputStreamWriter;

public class JavaIO2 {

    public static void main(String[] args) throws IOException {
        String Path="E:\\天才白痴梦\\JAVA";
        File file=new File("E:\\天才白痴梦\\JAVA","BaiYiShaoNian.txt");
        if (!file.exists()) {
            try {
                file.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        /**
         * Java写入文件的三种方法
         * */
        FileOutputStream fos=null;
        BufferedWriter bw=null;
        FileWriter fw=null;
        int value=1000;
        
        try {
            fos=new FileOutputStream(new File(Path+"fos.txt"));
            long begin=System.currentTimeMillis();
            for (int i=1; i<=value; i++) {
                fos.write(5);
            }
            long end=System.currentTimeMillis();
            System.out.println("TheCostTime of FileOutputStream is : " + (end-begin));
            fos.close();
            
            bw=new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File(Path+"br.txt")),"UTF8"));
            begin=System.currentTimeMillis();
            for (int i=1; i<=value; i++) {
                bw.write(5);
                bw.newLine();
            }
            bw.close();
            end=System.currentTimeMillis();
            System.out.println("TheCostTime of BufferedWriter is : " + (end-begin));
            
            fw=new FileWriter(Path+"fw.txt");
            begin=System.currentTimeMillis();
            for (int i=1; i<=value; i++) {
                fw.write(5);                
            }
            fw.close();
            end=System.currentTimeMillis();
            System.out.println("TheCostTime of FileWriter is : " + (end-begin));
            
            
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            try {
                fos.close(); //FileOutputStream
                bw.close(); //BufferedWriter
                fw.close(); //FileWriter
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        
    }
}