Java ObjectOutputStream writeFields()用法及代码示例

ObjectOutputStream类writeFields()方法

• writeFields() 方法可在java.io包。
• writeFields() 方法用于将缓冲字段写入 ObjectOutputStream。
• writeFields() 方法是一个非静态方法，它只能通过类对象访问，如果我们尝试使用类名访问方法，那么我们将得到一个错误。
• writeFields() 方法可能会在写入字段时抛出异常。
  • IOException:在写入输出流时出现任何输入/输出错误时，可能会抛出此异常。
  • 非活动异常: 当没有调用 writeObject() 来写入类对象的状态时，可能会抛出此异常。

用法:

    public void writeFields();

参数：

• 它不接受任何参数。

返回值：

该方法的返回类型是void，它什么都不返回。

例：

// Java program to demonstrate the example 
// of void writeFields() method of ObjectOutputStream

import java.io.*;

public class WriteFieldsOfOOS {
 public static void main(String[] args) throws Exception {
  // Instantiates ObjectOutputStream , ObjectInputStream 
  // FileInputStream and FileOutputStream
  FileOutputStream file_out_stm = new FileOutputStream("D:\\includehelp.txt");
  ObjectOutputStream obj_out_stm = new ObjectOutputStream(file_out_stm);
  FileInputStream file_in_stm = new FileInputStream("D:\\includehelp.txt");

  ObjectInputStream obj_in_stm = new ObjectInputStream(file_in_stm);

  // By using writeInt() method is to write
  // integer to the obj_out_stm stream
  obj_out_stm.writeObject(new ReadFields());

  obj_out_stm.flush();

  // By using readObject() method is to read
  //  object and display fields
  ReadFields rf = (ReadFields) obj_in_stm.readObject();
  System.out.println("obj_in_stm.writeFields():" + rf.val);
 }

 static public class ReadFields implements Serializable {
  static int val = 12685;

  private static final ObjectStreamField[] serialPersistentFields = {
   new ObjectStreamField("val", Integer.TYPE)
  };

  private void readObject(ObjectInputStream oin)
  throws IOException, ClassNotFoundException {

   // Invokes readFields()
   ObjectInputStream.GetField fi = oin.readFields();

   // By using get() is to get var
   val = fi.get("val", 0);
  }

  private void writeObject(ObjectOutputStream oos) throws IOException {
   // By using putFields() method is to
   // write var into ObjectStreamField[]
   ObjectOutputStream.PutField fi = oos.putFields();
   fi.put("val", val);

   // Invokes writeFields()
   oos.writeFields();
  }
 }
}

输出

obj_in_stm.writeFields():12685