13. IO流

一、文件
创建文件：

public class Home {
  public static void main(String[] args) {
    String filePath = "e:\\news1.txt";
    File file = new File(filePath);
    try {
      file.createNewFile();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}

二、IO流分类

image.png
image.png

三、节点流FileInputStream
文件字节输入流：

public class Home {
  public static void main(String[] args) {
    String filePath = "e:\\a.txt";
    byte[] buf = new byte[8];
    int readLen = 0;
    FileInputStream fileInputStream = null;
    try {
      fileInputStream = new FileInputStream(filePath);
      while ((readLen = fileInputStream.read(buf)) != -1) {
        System.out.print(new String(buf, 0, readLen));
      }

    } catch (IOException e) {
      e.printStackTrace();
    }finally{
      try {
        fileInputStream.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
}

四、节点流FileOutputStream
文件字节输出流：

public class Home {
  public static void main(String[] args) {
    String filePath = "e:\\a.txt";
    FileOutputStream  fileOutputStream =null;
    try {
      // 参数加true是追加内容，不加是覆盖
      fileOutputStream = new FileOutputStream(filePath);
      String str = "hello,world!";
      fileOutputStream.write(str.getBytes());
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      try {
        fileOutputStream .close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
}

四、节点流FileReader
文件字符输入流：

public class Home {
  public static void main(String[] args) {
    String filePath = "e:\\a.txt";
    FileReader fileReader = null;
    int readLen = 0;
    char[] buf = new char[8];
    try {
      fileReader = new FileReader(filePath);
      while ((readLen = fileReader.read(buf)) != -1) {
        System.out.print(new String(buf, 0, readLen));
      }
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      try {
        fileReader.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
}

五、节点流FileWriter
文件字符输出流：

public class Home {
  public static void main(String[] args) {
    String filePath = "e:\\a.txt";
    FileWriter fileWriter = null;
    try {
      fileWriter = new FileWriter(filePath);
      fileWriter.write(" 你好北京~");
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      try {
        fileWriter.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
}

六、处理流-BufferedReader
字符流输入流：

public class Home {
  public static void main(String[] args) {
    String filePath = "e:\\a.txt";
    String line;
    BufferedReader bufferedReader = null;
    try {
      bufferedReader = new BufferedReader(new FileReader(filePath));
      while ((line = bufferedReader.readLine()) != null) {
        System.out.println(line);
      }
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      try {
        bufferedReader.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
}

七、处理流-BufferedWriter
字符流输出流：

public class Home {
  public static void main(String[] args) {
    String filePath = "e:\\a.txt";
    BufferedWriter bufferedWriter = null;
    try {
      bufferedWriter = new BufferedWriter(new FileWriter(filePath));
      bufferedWriter.write("哈哈哈");
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      try {
        bufferedWriter.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
}

八、处理流-BufferedInputStream
字节输入流：

public class Home {
  public static void main(String[] args) {
    String filePath = "e:\\a.txt";
    BufferedInputStream bufferedInputStream = null;
    byte[] buff = new byte[1024];
    try {
      bufferedInputStream = new BufferedInputStream(new FileInputStream(filePath));
      while (bufferedInputStream.read(buff) != -1) {
        System.out.println(new String(buff));
      }

    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      try {
        bufferedInputStream.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
}

九、处理流-BufferedOutputStream
字节输出流：

public class Home {
  public static void main(String[] args) {
    String filePath = "e:\\a.txt";
    BufferedOutputStream bufferedOutputStream = null;
    try {
      bufferedOutputStream = new BufferedOutputStream(new FileOutputStream(filePath));
      bufferedOutputStream.write("xxx".getBytes());
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      try {
        bufferedOutputStream.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
}

十、对象流-ObjectInputStream

public class Home {
  public static void main(String[] args) {
    String filePath = "e:\\a.dat";
    ObjectInputStream objectInputStream = null;
    try {
      objectInputStream = new ObjectInputStream(new FileInputStream(filePath));
      System.out.println(objectInputStream.readObject()); // 这里返回的是object对象

    } catch (IOException | ClassNotFoundException e) {
      e.printStackTrace();
    } finally {
      try {
        objectInputStream.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
}

class Cat implements Serializable {
  private static final long serialVersionUID = 1L;
  private String name;

  public Cat(String name) {
    this.name = name;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }
}

十一、对象流ObjectOutputStream

public class Home {
  public static void main(String[] args) {
    String filePath = "e:\\a.dat";
    ObjectOutputStream oos = null;
    try {
      oos = new ObjectOutputStream(new FileOutputStream(filePath));
      oos.writeObject(new Cat("小黄"));
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      try {
        oos.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
}

class Cat implements Serializable {
  private static final long serialVersionUID = 1L;
  private String name;

  public Cat(String name) {
    this.name = name;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }
}

1. 序列化的类必须实现Serializable接口
2. 读写顺序要一致
3. 序列化中的类建议添加

十二、Properties
Properties是专门用于读写配置文件的集合类。格式是key=value

常见方法：

1. load 加载数据到properties对象
2. list 将数据显示到指定设备
3. getProperty(key) 根据key获取到value
4. setProperty(key, value)设置键值对到properties对象
5. store 将properties对象保存的键值对存储到配置文件中

//1. 创建 Properties 对象
Properties properties = new Properties();
//2. 加载指定配置文件
properties.load(new FileReader("src\\mysql.properties"));
//3. 把 k-v 显示控制台
properties.list(System.out);
//4. 根据 key 获取对应的值
String user = properties.getProperty("user");
String pwd = properties.getProperty("pwd");