Java的序列化機制原理分析

Java的序列化機制原理分析，我們查看下ObjectOutputStream的writeObject方法

1. //final方法，不允許子類覆蓋
2. public final void writeObject(Object obj) throws IOException {
3. if (enableOverride) { //如果開啟允許序列化被重寫
4. writeObjectOverride(obj); //調用子類的序列化重寫方法
5. return;
6. }
7. try {
8. writeObject0(obj, false);//調用默認的序列化過程
9. } catch (IOException ex) {
10. if (depth == 0) {
11. writeFatalException(ex);
12. }
13. throw ex;
14. }
15. }

如果要自定義這個序列化過程，則可以寫一個子類，集成ObjectOutputStream，然後覆蓋其兩個方法

1. protected ObjectOutputStream() throws IOException, SecurityException {
2. SecurityManager sm = System.getSecurityManager();
3. if (sm != null) {
4. sm.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
5. }
6. bout = null;
7. handles = null;
8. subs = null;
9. enableOverride = true;
10. debugInfoStack = null;
11. }
12. protected void writeObjectOverride(Object obj) throws IOException {
13. }

我們再看下具體的writeObject0方法：

1. private void writeObject0(Object obj, boolean unshared)
2. throws IOException
3. {
4. boolean oldMode = bout.setBlockDataMode(false);
5. depth++;
6. try {
7. // 先對obj實例的類信息進行序列化，
8. int h;
9. if ((obj = subs.lookup(obj)) == null) {
10. writeNull();
11. return;
12. } else if (!unshared && (h = handles.lookup(obj)) != -1) {//可以自定義class類信息的序列化handler
13. writeHandle(h);
14. return;
15. } else if (obj instanceof Class) { //類信息序列化
16. writeClass((Class) obj, unshared);
17. return;
18. } else if (obj instanceof ObjectStreamClass) { //類信息序列化，此時還包括serialVersionUID
19. writeClassDesc((ObjectStreamClass) obj, unshared);
20. return;
21. }
23. // check for replacement object
24. //這裡還可以對序列化的類進行替換序列化
25. Object orig = obj;
26. Class cl = obj.getClass();
27. ObjectStreamClass desc;
28. for (;;) {
29. // REMIND: skip this check for strings/arrays?
30. Class repCl;
31. desc = ObjectStreamClass.lookup(cl, true);
32. if (!desc.hasWriteReplaceMethod() ||
33. (obj = desc.invokeWriteReplace(obj)) == null ||
34. (repCl = obj.getClass()) == cl)
35. {
36. break;
37. }
38. cl = repCl;
39. }
40. if (enableReplace) {
41. Object rep = replaceObject(obj);
42. if (rep != obj && rep != null) {
43. cl = rep.getClass();
44. desc = ObjectStreamClass.lookup(cl, true);
45. }
46. obj = rep;
47. }
49. // if object replaced, run through original checks a second time
50. //如果類信息被替換過，則需要進行第二次處理
51. if (obj != orig) {
52. subs.assign(orig, obj);
53. if (obj == null) {
54. writeNull();
55. return;
56. } else if (!unshared && (h = handles.lookup(obj)) != -1) {
57. writeHandle(h);
58. return;
59. } else if (obj instanceof Class) {
60. writeClass((Class) obj, unshared);
61. return;
62. } else if (obj instanceof ObjectStreamClass) {
63. writeClassDesc((ObjectStreamClass) obj, unshared);
64. return;
65. }
66. }
68. // remaining cases
69. //寫入類實例對象的數據，第一次總是在此執行
70. if (obj instanceof String) {
71. writeString((String) obj, unshared);
72. } else if (cl.isArray()) {
73. writeArray(obj, desc, unshared);
74. } else if (obj instanceof Enum) {
75. writeEnum((Enum) obj, desc, unshared);
76. } else if (obj instanceof Serializable) { //我們的bean需要實現Serializable接口，才能進行序列化
77. writeOrdinaryObject(obj, desc, unshared);
78. } else {
79. if (extendedDebugInfo) {
80. throw new NotSerializableException(
81. cl.getName() + "\n" + debugInfoStack.toString());
82. } else {
83. throw new NotSerializableException(cl.getName());
84. }
85. }
86. } finally {
87. depth--;
88. bout.setBlockDataMode(oldMode);
89. }
90. }