transient 關鍵字
tansient是Java中的一個關鍵字,不過在日常的開發中我們很少用或者是遇到,我也是在
看ArrayList源代碼的時候發現其類中聲明的一個屬性值中用到了transient關鍵字,表示
這個屬性只是暫時的,究竟起到什麼作用呢?經過查閱發現transient的功能就是在將一個
對象序列化的時候帶transient關鍵字的屬性不會被序列化。下面通過具體的代碼來說明這
transient的作用。
package core.java.serializable;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class SerializableDemo {
public static void main(String[] args) {
SerializableDemo demo = new SerializableDemo();
System.out.println("開始序列化--------------");
User user = new User(1, "zhangsan", "男");
demo.writeObject(user);
System.out.println("開始反序列化--------------");
User u = (User)demo.readObject();
System.out.println(u.getId() + "," + u.getName() + "," + u.getSex());
}
/**
* 序列化對象
* @param obj
*/
private void writeObject(Object obj){
try {
ObjectOutputStream ots = new ObjectOutputStream(new FileOutputStream(new File("D:/object.txt")));
ots.writeObject(obj);
ots.flush();
ots.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* 反序列化對象
* @return
*/
private Object readObject(){
try {
ObjectInputStream ois = new ObjectInputStream(new FileInputStream(new File("D:/object.txt")));
Object object = ois.readObject();
ois.close();
return object;
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
return null;
}
}
package core.java.serializable;
import java.io.Serializable;
/**
* 序列化實體
* @author author
*
*/
public class User implements Serializable{
/**
*
*/
private static final long serialVersionUID = 8511909251520938165L;
private int id;
private String name;
private transient String sex;
public User(int id, String name, String sex){
super();
this.id = id;
this.name = name;
this.sex = sex;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
}
控制檯輸出:
開始序列化--------------
開始反序列化--------------
1,zhangsan,null
從控制檯輸出的值我們可以發現User的sex屬性值並沒有沒序列化。
是不是隻要是用了transient關鍵字的屬性就不會被序列化呢,其實並不是。我們都
知道要是一個對象實現序列化通過實現Serializable接口就可以,但是還有另外一種方法
實現對象序列化的方式就是實現Externalizable,實現Externalizable接口需要實現該接口
的兩個方法writeExternal和readExternal方法,需要手動指定哪些屬性將要被實現序列化。
代碼演示:
package core.java.serializable;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class SerializableDemo {
public static void main(String[] args) {
SerializableDemo demo = new SerializableDemo();
Address address = new Address(1, "中國", "北京", "朝陽區");
demo.writeObject(address);
Address add = (Address)demo.readObject();
System.out.println(add.getId() + "," + add.getCountry() + "," + add.getCity() + "," + add.getArea());
}
/**
* 序列化對象
* @param obj
*/
private void writeObject(Object obj){
try {
ObjectOutputStream ots = new ObjectOutputStream(new FileOutputStream(new File("D:/object.txt")));
ots.writeObject(obj);
ots.flush();
ots.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* 反序列化對象
* @return
*/
private Object readObject(){
try {
ObjectInputStream ois = new ObjectInputStream(new FileInputStream(new File("D:/object.txt")));
Object object = ois.readObject();
ois.close();
return object;
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
return null;
}
}
package core.java.serializable;
import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
/**
* Externalizable方式實現對象序列化
* @author author
*
*/
public class Address implements Externalizable{
private int id;
private String country;
private String city;
private transient String area;
public Address(){
}
public Address(int id, String country, String city, String area){
super();
this.id = id;
this.country = country;
this.city = city;
this.area = area;
}
@Override
public void writeExternal(ObjectOutput out) throws IOException {
out.writeObject(id);
out.writeObject(country);
out.writeObject(city);
out.writeObject(area);
}
@Override
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
id = (int) in.readObject();
country = (String) in.readObject();
city = (String) in.readObject();
area = (String) in.readObject();
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getArea() {
return area;
}
public void setArea(String area) {
this.area = area;
}
}
控制檯輸出
1,中國,北京,朝陽區
從控制檯打印出來的結果可以知道並不是用transient聲明的屬性就不能被序列化。