把對(duì)象轉(zhuǎn)換為字節(jié)序列的過程稱為對(duì)象的序列化，把字節(jié)序列恢復(fù)為對(duì)象的過程稱為對(duì)象的反序列化。
對(duì)象的序列化主要有兩種途徑：
Ⅰ . 把對(duì)象的字節(jié)序列永久地保存到硬盤上，通常存放在一個(gè)文件中
Ⅱ. 在網(wǎng)絡(luò)上傳送對(duì)象的字節(jié)序列。
當(dāng)兩個(gè)進(jìn)程在進(jìn)行遠(yuǎn)程通信時(shí)，彼此可以發(fā)送各種類型的數(shù)據(jù)。無論是何種類型的數(shù)據(jù)，都會(huì)以二進(jìn)制序列的形式在網(wǎng)絡(luò)上傳送。發(fā)送方需要把這個(gè)Java對(duì)象轉(zhuǎn)換為字節(jié)序列，才能在網(wǎng)絡(luò)上傳送；接收方則需要把字節(jié)序列再恢復(fù)為Java對(duì)象。
二、序列化API
1. 對(duì)象輸出流（ObjectOutputStream）的常用方法：
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// 創(chuàng)建寫入指定 OutputStream 的 ObjectOutputStream。此構(gòu)造方法將序列化流部分寫入底層流 public ObjectOutputStream(OutputStream out) throws IOException // 將指定的對(duì)象寫入 ObjectOutputStream public final void writeObject(Object obj) throws IOException |
2. 對(duì)象輸入流（ObjectInputStream）的常用方法：
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// 創(chuàng)建從指定 InputStream 讀取的 ObjectInputStream。 public ObjectInputStream(InputStream in) throws IOException // 從 ObjectInputStream 讀取對(duì)象。對(duì)象的類、類的簽名和類及所有其超類型的非瞬態(tài)和非靜態(tài)字段的值都將被讀取。 public final Object readObject() throws IOException, ClassNotFoundException |
范例：對(duì)象序列化與反序列化
①. 定義一個(gè)Person類，實(shí)現(xiàn)Serializable接口
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public class Person implements Serializable { /** * 序列化ID */ private static final long serialVersionUID = 3817849972563375707L; private String name; private int age; private String sex; public String getName() {return name; } public void setName(String name) {this.name = name; } public int getAge() {return age; } public void setAge(int age) {this.age = age; } public String getSex() {return sex; } public void setSex(String sex) {this.sex = sex; } } |
②. 序列化和反序列化Person類對(duì)象
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public class TestObjSerializeAndDeserialize { public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException { serializePerson(); Person person = deserializePerson(); System.out.println(MessageFormat.format("name={0},age={1},sex={2}", person.getName(), person.getAge(), person.getSex())); } /** * 反序列化Person對(duì)象 * * @throws IOException * @throws FileNotFoundException * @throws ClassNotFoundException */ private static Person deserializePerson() throws FileNotFoundException, IOException, ClassNotFoundException { ObjectInputStream in = new ObjectInputStream(new FileInputStream( new File("E:\\person.txt"))); Person person = (Person) in.readObject(); System.out.println("反序列化成功！"); return person; } /** * 序列化Person對(duì)象 * * @throws IOException * @throws FileNotFoundException */ private static void serializePerson() throws FileNotFoundException, IOException { Person person = new Person(); person.setName("pegasus"); person.setAge(24); person.setSex("男"); ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream( new File("E:\\person.txt"))); out.writeObject(person); System.out.println("對(duì)象序列化成功！"); out.close(); } } |
運(yùn)行如圖所示：
三、serialVersionUID的作用
將對(duì)象序列化與反序列化范例中的serialVersionUID從Person類中去除，從新運(yùn)行程序，結(jié)果會(huì)發(fā)現(xiàn)對(duì)象序列化成功、反序列化也成功了。現(xiàn)在添加一個(gè)屬性address，如下：
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public class Person implements Serializable { private String name; private int age; private String sex; private String address; public String getName() {return name; } public void setName(String name) {this.name = name; } public int getAge() {return age; } public void setAge(int age) {this.age = age; } public String getSex() {return sex; } public void setSex(String sex) {this.sex = sex; } public String getAddress() {return address; } public void setAddress(String address) {this.address = address; } @Override public String toString() { return "Person [name=" + name + ", age=" + age + ", sex=" + sex + ", address=" + address + "]"; } } |
然后執(zhí)行反序列操作：
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public class DeserializePerson { public static void main(String[] args) throws FileNotFoundException, ClassNotFoundException, IOException { Person person = deserializePerson(); System.out.println(person); } /** * 反序列化Person對(duì)象 * * @throws IOException * @throws FileNotFoundException * @throws ClassNotFoundException */ private static Person deserializePerson() throws FileNotFoundException, IOException, ClassNotFoundException { ObjectInputStream in = new ObjectInputStream(new FileInputStream( new File("E:\\person.txt"))); Person person = (Person) in.readObject(); System.out.println("反序列化成功！"); return person; } } |
運(yùn)行發(fā)現(xiàn)，會(huì)出現(xiàn)如下錯(cuò)誤：
Exception in thread "main" java.io.InvalidClassException: com.pegasus.serializable.Person; local class incompatible: stream classdesc serialVersionUID = 2521373692768252888, local class serialVersionUID = -6354757228515182324
意思是，文件流中的class和修改過后的class，不兼容了，處于安全機(jī)制考慮，程序拋出錯(cuò)誤，而且拒絕載入。如果我們真的需要在序列化后添加一個(gè)字段或者方法，應(yīng)該怎么辦？其實(shí)也很簡(jiǎn)單，只需自己去指定serialVersionUID即可。在上面的例子中，沒有給Person類指定serialVersionUID，那么java編譯器會(huì)自動(dòng)給這個(gè)class生成一個(gè)serialVersionUID，只要對(duì)這個(gè)文件添加一個(gè)空格，得到的UID都會(huì)不同，這個(gè)編號(hào)是唯一的。所以，添加一個(gè)字段后，由于沒有顯示指定serialVersionUID，編譯器又為我們生成一個(gè)UID，當(dāng)然和前面保存在文件中的哪一個(gè)不一樣，于是出現(xiàn)兩個(gè)版本號(hào)不一致的錯(cuò)誤。因此，只要自己指定serialVersionUID，就可在序列化以后，去添加一個(gè)字段，或者方法，而不會(huì)影響后期的反序列化，反序列后的對(duì)象還會(huì)多了方法和屬性。
下面將Person類中指定serialVersionUID，重新執(zhí)行序列化操作，將Person對(duì)象序列化到本地硬盤的Person.txt文件存儲(chǔ)，然后修改Person類，之后再次反序列化測(cè)試，將會(huì)發(fā)現(xiàn)程序就沒有異常了。
四、transient
當(dāng)使用Serializable接口實(shí)現(xiàn)序列化操作時(shí)，如果一個(gè)對(duì)象中的某個(gè)屬性不希望被序列化的話，則可以使用transient關(guān)鍵字進(jìn)行聲明。如下面的示例：
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public class Customer implements Serializable{ private static final long serialVersionUID = -4020382581484304699L; private String name; private transient String address; // 此屬性不被序列化 public Customer(String name, String address) { this.name = name; this.address = address; } @Override public String toString() { return "Customer [name=" + name + ", address=" + address + "]"; } } |
序列化、反序列化Customer，代碼如下：
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public class TestCustomer { public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException { serializeCustomer(); deserializeCustomer(); } private static void deserializeCustomer() throws FileNotFoundException, IOException, ClassNotFoundException { ObjectInputStream in = new ObjectInputStream(new FileInputStream( new File("E:\\customer.txt"))); Customer customer = (Customer) in.readObject(); System.out.println(customer); in.close(); } private static void serializeCustomer() throws FileNotFoundException, IOException { ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream( new File("E:\\customer.txt"))); out.writeObject(new Customer("pegasus", "甘肅")); System.out.println("序列化成功!"); out.close(); } } |
結(jié)果如下：
以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持服務(wù)器之家。
原文鏈接：http://blog.csdn.net/qq_25583079/article/details/48624425
