Android中跨进程通信方式之使用文件共享

一、使用Serializable序列化对象

import java.io.Serializable;

public class User implements Serializable{
    private static final long serialVersionUID  = 1L;
    private String username;
    private String password;
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }

}

serialVersionUID是序列化对象时向文件写入的一个UID，其目地是为了反序列化恢复该对象时，防止增加或删除一些字段或者改动某个类型，导致类的版本不同，恢复错误。
序列化过程：

        User user = new User();
        user.setUsername("zhangsan");
        user.setPassword("123");
        ObjectOutputStream os = null;
        try {
            os = new ObjectOutputStream(new FileOutputStream(getFilesDir()+"cache.txt"));
            os.writeObject(user);
        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            try {
                os.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

反序列化恢复过程：

        ObjectInputStream is = null;
        try {
            is = new ObjectInputStream(new FileInputStream(getFilesDir()+"cache.txt"));
            User newUser = (User) is.readObject();
            tv.setText(newUser.getUsername());
        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

二、使用Parcelable序列化对象

import android.os.Parcel;
import android.os.Parcelable;

public class Student implements Parcelable{
    private String username;
    private String password;
    public Student(){
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    @Override
    public int describeContents() {
        return 0;
    }
    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(username);
        dest.writeString(password);
    }
    public static final Parcelable.Creator<Student> CREATOR = new Creator<Student>() {

        @Override
        public Student[] newArray(int size) {
            return new Student[size];
        }

        @Override
        public Student createFromParcel(Parcel source) {
            return new Student(source);
        }
    };
    private Student(Parcel source){
        username = source.readString();
        password = source.readString();
    }

}

writeToParcel方法将实现序列化，通过Parcel的write方法实现。CREATOR 实现反序列化，通过Parcel的read方法实现。

这样便可以通过Intent，bundle传递Parcelable对象了。

                Intent intent = new Intent();
                intent.setClass(MainActivity.this, SecondActivity.class);
                Bundle bundle = new Bundle();
                Student student = new Student();
                student.setUsername("lisi");
                student.setPassword("456");
                bundle.putParcelable("student", student);
                intent.putExtras(bundle);
                startActivity(intent);

Serializable需要大量的I/O操作，需要将序列化的对象存储在设备或者网络传输时适用。
Parcelable是安卓的序列化方式，使用比较麻烦，但效率高。

注意：当Parcelable对象中有对象时，这个对象必须是Parcelable或者Serializable类型的。
序列化方式如下：

//user为Serializable
private User user;
dest.writeSerializable(user);
user = (User) source.readSerializable();
//teacher为Parcelable
private Teacher teacher;
dest.writeParcelable(teacher, 0);
//传递当前线程的上下文类加载器
teacher = source.readParcelable(Thread.currentThread().getContextClassLoader());