java基础-io(字符流)

1. 编码问题

java的文本(char)是16位无符号整数，是字符的unicode编码(双字节编码)

文本是byte byte byte..的数据序列

文本文件是文本(char)序列按照某种编码方案(utf-8,utf-16be,gbk)序列化为byte的存储

2.字符流 Reader/Writer　　　　--操作的是文本文本文件(gbk编码)

 字符的处理，一个字符一个字符的处理

字符的底层依旧是字节序列

InputStreamReader 完成byte流解析为char流，按照编码解析

OutputStreamWriter 提供char流到byte流，按照编码处理

public static void main(String[] args) {
        InputStreamReader inputStreamReader = null;
        OutputStreamWriter outputStreamWriter = null;
        try {
            inputStreamReader = new InputStreamReader(new FileInputStream("demo/demo.dat"), "utf-8");    //默认项目的编码就是
//            int c;
//            while ((c = inputStreamReader.read()) != -1){
//                System.out.println((char)c);
//            }
            outputStreamWriter = new OutputStreamWriter(new FileOutputStream("demo/dos.dat"), "utf-8");
            char[] buffer = new char[8 * 1024];
            int c;
            while ((c = inputStreamReader.read(buffer, 0, buffer.length)) != -1) {
                String s = new String(buffer, 0, c);
                System.out.println(s);
                outputStreamWriter.write(buffer, 0, c);
            }
            outputStreamWriter.flush();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (inputStreamReader != null) {
                    inputStreamReader.close();
                }
                if (outputStreamWriter != null) {
                    outputStreamWriter.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

　　

3. FileReader/FileWriter 

public class FileReaderAndWriter {
    public static void main(String[] args) {
        FileReader fileReader = null;
        FileWriter fileWriter = null;
        try {
            fileReader = new FileReader("demo/raf.dat");
            fileWriter = new FileWriter("demo/dos.dat", true);      //true追加
            char[] buffer = new char[8 * 1024];
            int c;
            while ((c = fileReader.read(buffer, 0, buffer.length)) != -1) {
                fileWriter.write(buffer, 0, c);
            }
            fileWriter.flush();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (fileReader != null) {
                    fileReader.close();
                }
                if (fileWriter != null) {
                    fileWriter.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

　　

4. 字符流过滤器

public static void main(String[] args) {
        //对文件进行操作
        BufferedReader bufferedReader = null;
        BufferedWriter bufferedWriter = null;
        PrintWriter printWriter = null;
        try {
            bufferedReader = new BufferedReader(new InputStreamReader(new FileInputStream("demo/demo.dat")));
            bufferedWriter = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("demo/dos.dat", true)));
            printWriter = new PrintWriter("demo/dos.dat");
            String line;
            while ((line = bufferedReader.readLine()) != null) {
//                System.out.println(line);
//                bufferedWriter.write(line);
//                bufferedWriter.newLine();       //识别换行
                printWriter.println(line);
            }

            bufferedWriter.flush();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (bufferedReader != null) {
                    bufferedReader.close();
                }
                if (bufferedWriter != null) {
                    bufferedWriter.close();
                }
                if (printWriter != null) {
                    printWriter.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

　　

5.序列化

5.1 对象的序列化与反序列化

就是将object对象转换成byte序列，反之就是反序列化

序列化流(ObjectOutputStream)是过滤流----->writeObject

反序列化流(ObjectInputStream)---->readObject

5.2 序列化接口(Serializable)

对象必须实现序列化接口，才能进行序列化，否则将出现异常

这个接口没有任何方法，只是一个规定

序列化

public class ObjectSeriDemo {

    public static void main(String[] args) {
        String file = "demo/obj.dat";
        ObjectOutputStream objectOutputStream = null;
        //1.对象的序列化
        try {
            objectOutputStream = new ObjectOutputStream(new FileOutputStream(file));
            Student student = new Student(1,"张三");
            objectOutputStream.writeObject(student);
            objectOutputStream.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (objectOutputStream != null) {
                    objectOutputStream.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

　　

反序列化

public class ObjectSeriDemo {

    public static void main(String[] args) {
        String file = "demo/obj.dat";
        ObjectInputStream objectInputStream = null;
        try {
            objectInputStream = new ObjectInputStream(new FileInputStream(file));
            Student student = (Student) objectInputStream.readObject();
            System.out.println(student.toString());
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } finally {
            try {
                if (objectInputStream != null) {
                    objectInputStream.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

　　

5.3 transient

该关键字的作用是当序列化对象时，其中有不想要jvm序列化元素的时候，就需要在元素前加上该关键字。

也可以自己完成序列化工作

自定义序列化

在需要序列化的model类中增加这两个方法，首先反/序列化jvm能序列化的元素，再序列化自己需要自定义序列化的元素

　　private void writeObject(java.io.ObjectOutputStream s)
            throws java.io.IOException{
        s.defaultWriteObject();     //序列化jvm能默认序列化的元素
        s.writeObject(name);
    }

    private void readObject(java.io.ObjectInputStream s)
            throws java.io.IOException, ClassNotFoundException {
        s.defaultReadObject();      //把jvm默认反序列的元素进行反序列化操作
        this.name = (String) s.readObject();
    }