Java 序列化實現深層複製：效能對比與穩定性分析

對象序列化後再反序列化，實質經歷一個「複製」過程。為何不直接用序列化做深層複製？以下程式碼對比兩種方法效能：

//: Compete.java
import java.io.*;
class Thing1 implements Serializable {}
class Thing2 implements Serializable { Thing1 o1 = new Thing1(); }
class Thing3 implements Cloneable {
    public Object clone() {
        Object o = null;
        try { o = super.clone(); }
        catch (CloneNotSupportedException e) { System.out.println("Thing3 can't clone"); }
        return o;
    }
}
class Thing4 implements Cloneable {
    Thing3 o3 = new Thing3();
    public Object clone() {
        Thing4 o = null;
        try { o = (Thing4)super.clone(); }
        catch (CloneNotSupportedException e) { System.out.println("Thing4 can't clone"); }
        o.o3 = (Thing3)o3.clone(); // 深層複製欄位
        return o;
    }
}
public class Compete {
    static final int SIZE = 5000;
    public static void main(String[] args) {
        Thing2[] a = new Thing2[SIZE];
        for(int i = 0; i < a.length; i++) a[i] = new Thing2();
        Thing4[] b = new Thing4[SIZE];
        for(int i = 0; i < b.length; i++) b[i] = new Thing4();
        try {
            // 序列化複製
            long t1 = System.currentTimeMillis();
            ByteArrayOutputStream buf = new ByteArrayOutputStream();
            ObjectOutputStream o = new ObjectOutputStream(buf);
            for(int i = 0; i < a.length; i++) o.writeObject(a[i]);
            ObjectInputStream in = new ObjectInputStream(
                new ByteArrayInputStream(buf.toByteArray()));
            Thing2[] c = new Thing2[SIZE];
            for(int i = 0; i < c.length; i++) c[i] = (Thing2)in.readObject();
            long t2 = System.currentTimeMillis();
            System.out.println("Duplication via serialization: " + (t2 - t1) + " Milliseconds");
            // Clone 複製
            t1 = System.currentTimeMillis();
            Thing4[] d = new Thing4[SIZE];
            for(int i = 0; i < d.length; i++) d[i] = (Thing4)b[i].clone();
            t2 = System.currentTimeMillis();
            System.out.println("Duplication via cloning: " + (t2 - t1) + " Milliseconds");
        } catch(Exception e) { e.printStackTrace(); }
    }
} ///:~

Thing2/Thing4 含成員物件，需深層複製。序列化設定簡單但複製耗時；Clone 類別設定繁瑣但實際複製極快。

多次執行結果

Duplication via serialization: 3400 Milliseconds
Duplication via cloning: 110 Milliseconds
Duplication via serialization: 3410 Milliseconds
Duplication via cloning: 110 Milliseconds
Duplication via serialization: 3520 Milliseconds
Duplication via cloning: 110 Milliseconds

序列化比 Clone 慢 30 倍以上，且時間波動大；Clone 每次耗時穩定。除非極度重視開發便利性，效能敏感場合首選 clone()。