android 進程間通信數據（一）------parcel的起源

關于parcel，我們先來講講它的“父輩”?Serialize。

Serialize 是java提供的一套序列化機制。但是為什么要序列化，怎么序列化，序列化是怎么做到的，我們將在本文探討下。

一：java 中的serialize

關于Serialize這個東東，think in java其實說的很詳細，大意如下：

1.Serialize的目的

當你創建對象時，你需要，它一直存在，但是當程序終止時，它就消失了。

如果程序不運行的情況下，可以保存某些信息，這將非常有用。

如何我程序在下次運行的時候，可以把上次運行的某些信息恢復回來.

2.Serialize的使用：

?使用一個嵌套的Serializable對象

package com.joyfulmath.androidstudy.bind.worm;import java.io.Serializable;public class Data implements Serializable {private int n;public Data(int n) {this.n = n;}@Overridepublic String toString() {return Integer.toString(n);}}

package com.joyfulmath.androidstudy.bind.worm;import java.io.Serializable;
import java.util.Random;import com.joyfulmath.androidstudy.TraceLog;public class Worm implements Serializable {static Random rand = new Random(47);Data[] d = {new Data(rand.nextInt(10)),new Data(rand.nextInt(10)),new Data(rand.nextInt(10))};private Worm next;private char c;public Worm(int i, char x){TraceLog.i("Worm construct:"+i);c = x;if(--i>0){next = new Worm(i,(char) (x+1));}}public Worm(){TraceLog.i("default Worm construct");}@Overridepublic String toString() {StringBuilder result = new StringBuilder(":");result.append(c);result.append("(");for(Data dat:d){result.append(dat+" ");}result.append(")");if(next!=null){result.append(next);}return result.toString();}}

驗證序列化的讀寫：

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;import com.joyfulmath.androidstudy.TraceLog;public class WormSample {static final String path = "/mnt/sdcard/worm.out";public void doAction(){Worm w = new Worm(6, 'a');TraceLog.i("\n"+w.toString());try {ObjectOutputStream opt = new ObjectOutputStream(new FileOutputStream(path));opt.writeObject("Worm object\n");opt.writeObject(w);opt.close();ObjectInputStream in = new ObjectInputStream(new FileInputStream(path));String s = (String) in.readObject();Worm w2 = (Worm) in.readObject();TraceLog.i(s+w);} catch (FileNotFoundException e) {// TODO Auto-generated catch block
            e.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch block
            e.printStackTrace();} catch (ClassNotFoundException e) {// TODO Auto-generated catch block
            e.printStackTrace();}}
}

最后log：

08-15 09:18:20.384: I/Worm(28437): <init>: Worm construct:6 [at (Worm.java:21)]
08-15 09:18:20.384: I/Worm(28437): <init>: Worm construct:5 [at (Worm.java:21)]
08-15 09:18:20.384: I/Worm(28437): <init>: Worm construct:4 [at (Worm.java:21)]
08-15 09:18:20.384: I/Worm(28437): <init>: Worm construct:3 [at (Worm.java:21)]
08-15 09:18:20.384: I/Worm(28437): <init>: Worm construct:2 [at (Worm.java:21)]
08-15 09:18:20.384: I/Worm(28437): <init>: Worm construct:1 [at (Worm.java:21)]
08-15 09:18:20.384: I/WormSample(28437): doAction: 
08-15 09:18:20.384: I/WormSample(28437): :a(853):b(119):c(802):d(788):e(199):f(881) [at (WormSample.java:18)]
08-15 09:18:20.414: I/WormSample(28437): doAction: Worm object
08-15 09:18:20.414: I/WormSample(28437): :a(853):b(119):c(802):d(788):e(199):f(881) [at (WormSample.java:28)]

可以看到，數據被很好的還原了，包含內部的序列化對象！

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二：parcel

Serializable是java定義的一套序列化機制，但是他是操作文件來執行的。或者說，它的性能無法滿足android上的要求，

這樣，parcel被google發明出來，用以取代Serializable。

1.Parcelable 的使用

package com.joyfulmath.androidstudy.bind.worm;import android.os.Parcel;
import android.os.Parcelable;public class DataP implements Parcelable {public int n;public DataP(int n) {this.n = n;}@Overridepublic int describeContents() {return 0;}@Overridepublic void writeToParcel(Parcel dest, int flags) {dest.writeInt(n);}public static final Parcelable.Creator<DataP> CREATOR = new Parcelable.Creator<DataP>() {public DataP createFromParcel(Parcel in) {return new DataP(in);}public DataP[] newArray(int size) {return new DataP[size];}};private DataP(Parcel in) {n = in.readInt();}@Overridepublic String toString() {return Integer.toString(n);}}

package com.joyfulmath.androidstudy.bind.worm;import java.util.Random;import com.joyfulmath.androidstudy.TraceLog;import android.os.Parcel;
import android.os.Parcelable;public class WormP implements Parcelable {static Random rand = new Random(47);public DataP[] d = { new DataP(rand.nextInt(10)), new DataP(rand.nextInt(10)),new DataP(rand.nextInt(10)) };private WormP next;public byte c;public WormP(int i,byte x){TraceLog.i("Wormp construct:"+i);c = x;if(--i>0){next = new WormP(i,(byte) (x+1));}}@Overridepublic int describeContents() {return 0;}@Overridepublic void writeToParcel(Parcel dest, int flags) {dest.writeByte(c);dest.writeParcelableArray(d, 0);if (next != null) {dest.writeParcelable(next, 0);}}public static final Parcelable.Creator<WormP> CREATOR = new Parcelable.Creator<WormP>() {public WormP createFromParcel(Parcel in) {return new WormP(in);}public WormP[] newArray(int size) {return new WormP[size];}};private WormP(Parcel in) {c = in.readByte();d = (DataP[]) in.readParcelableArray(DataP.class.getClassLoader());}@Overridepublic String toString() {StringBuilder result = new StringBuilder(":");result.append(c);result.append("(");for(DataP dat:d){result.append(dat+" ");}result.append(")");if(next!=null){result.append(next);}return result.toString();}
}

parcel一般使用在intent的內容的傳遞，所以本處做一個簡單的模擬：

    public void doActionP(){TraceLog.i();byte a = 'a';WormP w = new WormP(6, a);TraceLog.i(w.toString());Intent intent = new Intent();intent.putExtra("wormp", w);///...
        Intent newIntent = new Intent(intent);WormP w2 = newIntent.getParcelableExtra("wormp");TraceLog.i(w2.toString());TraceLog.i("end");}

08-15 10:14:11.924: I/WormSample(20183): doActionP:  [at (WormSample.java:47)]
08-15 10:14:11.934: I/WormP(20183): <init>: Wormp construct:6 [at (WormP.java:21)]
08-15 10:14:11.934: I/WormP(20183): <init>: Wormp construct:5 [at (WormP.java:21)]
08-15 10:14:11.934: I/WormP(20183): <init>: Wormp construct:4 [at (WormP.java:21)]
08-15 10:14:11.934: I/WormP(20183): <init>: Wormp construct:3 [at (WormP.java:21)]
08-15 10:14:11.934: I/WormP(20183): <init>: Wormp construct:2 [at (WormP.java:21)]
08-15 10:14:11.934: I/WormP(20183): <init>: Wormp construct:1 [at (WormP.java:21)]
08-15 10:14:11.934: I/WormSample(20183): doActionP: :97(8 5 3 ):98(1 1 9 ):99(8 0 2 ):100(7 8 8 ):101(1 9 9 ):102(8 8 1 ) [at (WormSample.java:50)]
08-15 10:14:11.934: I/WormSample(20183): doActionP: :97(8 5 3 ):98(1 1 9 ):99(8 0 2 ):100(7 8 8 ):101(1 9 9 ):102(8 8 1 ) [at (WormSample.java:59)]
08-15 10:14:11.934: I/WormSample(20183): doActionP: end [at (WormSample.java:61)]

可以看到結果，數據完全正確。

以上就是parcel的使用方式，在下一篇，將探索parcel的實現方式。

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參考：

http://blog.csdn.net/niu_gao/article/details/6451699

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