JavaSE:16、Java IO

学习资源1

学习资源 2

1、文件字节流


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args)  {
         //try-with-resource语法,自动close
            try(FileInputStream file = new FileInputStream("E:/text.txt")) {
                System.out.println("");
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

读入


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args)  {
         //try-with-resource语法,自动close
            try(FileInputStream file = new FileInputStream("E:/text.txt")) {
           int i;
            while((i=file.read())!=-1) {  //读一个字符，没有返回-1
                System.out.print((char) i);
            }
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args)  {
         //try-with-resource语法,自动close
            try(FileInputStream file = new FileInputStream("E:/text.txt")) {
          byte[] b = new byte[3];
          while(file.read(b)!=-1)   //一次读入三个字符
          {
              System.out.println(new String(b));
          }
             //   Hel
                //   lo
               // Wor
                 //    ldr
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args)  {
         //try-with-resource语法,自动close
            try(FileInputStream file = new FileInputStream("E:/text.txt")) {
          byte[] b = new byte[file.available()];//返回有多少个字节可读
          file.read(b);
              System.out.println(new String(b));
             //Hello World
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

输出


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args)  {
         //覆盖文件原有内容
            try(FileOutputStream file = new FileOutputStream("E:/text.txt")) {
            file.write("hello".getBytes());//字符串转为byte数组才行
            file.write("world".getBytes(),2,3);
            //hellorld;
            file.flush(); //刷新
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args)  {
         //在文件后面接着写

            try(FileOutputStream file = new FileOutputStream("E:/text.txt",true)) {
            file.write("hello".getBytes());//字符串转为byte数组才行
            file.write("world".getBytes(),2,3);
            //hellorldhellorld
            file.flush(); //刷新
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

文件拷贝


    import java.io.*;
    import java.util.*;

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

            try(FileOutputStream outputStream = new FileOutputStream("E:/textout.txt");
                FileInputStream inputStream = new FileInputStream("E:/text.txt")) {
                byte[] bytes = new byte[10];    //使用长度为10的byte[]做传输媒介
                int tmp;   //存储本地读取字节数
                while ((tmp = inputStream.read(bytes)) != -1) {   //直到读取完成为止
                    outputStream.write(bytes, 0, tmp);
                }
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

2、文件字符流

读纯文本文件，一次读一个字符，中英文均可

读入


    import java.io.*;
    import java.util.*;

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

            try(FileReader reader = new FileReader(new File("src/in.txt"))) {
            System.out.println(reader.read());//你
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

输出


    import java.io.*;
    import java.util.*;

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

            try(FileWriter  writer = new FileWriter("src/our.txt");) {
            writer.write("Hello World");//不用转为byte数组
                writer.flush();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

拷贝文件


    import java.io.*;
    import java.util.*;

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

            try(FileWriter  writer = new FileWriter("src/out.txt");
               FileReader reader = new FileReader("src/in.txt")) {
             char[]  c=new char[100];
             int len;
             while((len=reader.read(c))!=-1)
                 writer.write(c,0,len);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

3、文件对象


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args)  {
           File file=new File("src/in.txt");
           System.out.println(file.exists());//true
           System.out.println(file.isFile());//true
           System.out.println(file.getAbsolutePath());//该文件的绝对路径

        }
    }


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args) throws IOException {
           File file=new File("filetest");
           file.mkdir();//创建文件夹
           file=new File("filetest/test.txt");
           file.createNewFile();//创建文件
        }
    }

文件拷贝+进度条


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args) throws IOException {
           File file=new File("src/in.txt");
           try(FileInputStream in=new FileInputStream(file);
            FileOutputStream out=new FileOutputStream("src/out.txt")) {
            byte[]  by=new byte[20];
            long len=file.length();
            long sum=0;  int chalen;
            while((chalen=in.read(by))!=-1)
            {
                sum+=chalen;
                out.write(by,0,chalen);
                System.out.println("已拷贝："+(double)sum/len*100+"%");
//                已拷贝：12.658227848101266%
//                    已拷贝：25.31645569620253%
//                    已拷贝：37.9746835443038%
//                    已拷贝：50.63291139240506%
//                    已拷贝：63.29113924050633%
//                    已拷贝：75.9493670886076%
//                    已拷贝：88.60759493670885%
//                    已拷贝：100.0%
            }
           }catch (Exception e)
           {
               e.getStackTrace();
           }
        }
    }

4、缓冲流

缓冲字节流


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args)  {
           try(BufferedInputStream in=new BufferedInputStream(new FileInputStream("src/in.txt"));)
           {
               in.mark(0);
               System.out.print((char)in.read());
               System.out.print((char)in.read());
               System.out.println((char)in.read());//hel
               in.reset(); //从mark处开始读
                System.out.print((char)in.read());
               System.out.print((char)in.read());
               System.out.print((char)in.read());//hel
           }
           catch(Exception e)
           {
               e.getStackTrace();
           }
        }
    }


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args)  {
           try(BufferedOutputStream out=new BufferedOutputStream(new FileOutputStream("src/out.txt"));)
           {
               out.write("Hello World!".getBytes());;
           }
           catch(Exception e)
           {
               e.getStackTrace();
           }
        }
    }

缓冲字符流


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args)  {
           try(BufferedReader in=new BufferedReader(new FileReader("src/in.txt"));)
           {
               System.out.println(in.readLine());//helloworld
           }
           catch(Exception e)
           {
               e.getStackTrace();
           }
        }
    }


    import java.io.*;
    import java.util.*;

    public class Main {
        public static  void main(String[] args)  {
           try(BufferedWriter out=new BufferedWriter(new FileWriter("src/out.txt"));)
           {
               out.write("hello");
               out.newLine();
               out.write("world");
//               hello 
//               world
           }
           catch(Exception e)
           {
               e.getStackTrace();
           }
        }
    }

5、转换流


    import java.io.*;
    import java.util.*;

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

            try(OutputStreamWriter out=new OutputStreamWriter(new FileOutputStream("src/out.txt"));)
            {
                out.write("你好");
            }
            catch(Exception e)
            {
                e.getStackTrace();
            }
        }
    }


    import java.io.*;
    import java.util.*;

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

            try(InputStreamReader in=new InputStreamReader(new FileInputStream("src/in.txt"));)
            {
                System.out.println((char)in.read());//你
                System.out.println((char)in.read());//好
            }
            catch(Exception e)
            {
                e.getStackTrace();
            }
        }
    }

6、打印流


    import java.io.*;
    import java.util.*;

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

            try (PrintStream out = new PrintStream(new FileOutputStream("src/out.txt"));) {
                out.println("Hello World!");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

7、数据流和对象流

数据流（使用情况少，了解）


    import java.io.*;
    import java.util.*;

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

            try (DataInputStream in = new DataInputStream(new FileInputStream("src/in.txt"));) {
                System.out.println((char)in.readByte());//2
                
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

对象流


    import java.io.*;
    import java.util.*;

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

            try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("src/out.txt"));
                ObjectInputStream in = new ObjectInputStream(new FileInputStream("src/out.txt"))) {
               List<String> list=new ArrayList<>(Arrays.asList("A", "B", "C", "D", "E"));
              out.writeObject(list);
             //�� sr java.util.ArrayListx����a� I sizexp   w   t At Bt Ct Dt Ex
                Object o=in.readObject();
                System.out.println(o);
              //  [A, B, C, D, E]
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

对于自已定义的类需要实现序列化才能写读


    import java.io.*;
    import java.util.*;

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

            try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("src/out.txt"));
                ObjectInputStream in = new ObjectInputStream(new FileInputStream("src/out.txt"))) {
             Person person = new Person();
             person.name= "zhangsan";
             out.writeObject(person);
             Person person1 = (Person) in.readObject();
             System.out.println(person1.name);//zhangsan
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        static class Person implements Serializable {
            String name;
//transient  忽略该变量
        }
    }