java序列化

java通过serialVersionUID来控制对象的序列化、反序列化。当我们示设置serialVersionUID时，会通过类的名字、域的名字、方法的名字及已实现的接口生成一个隐式的serialVersionUID。所以类在后续的版本中，如果开发人员修改过代码，会引起serialVersionUID的值发生改变。这样原来的代码就无法向下兼容。例子如下： package serial; import java.io.Serializable; import net.sf.json.JSONObject; /** * @author blmcz * */ public class Person implements Serializable { // private static final long serialVersionUID = -1313015104027874116L; private String name; private String birthday; private String sex; private String mobile; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getBirthday() { return birthday; } public void setBirthday(String birthday) { this.birthday = birthday; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public String getMobile() { return mobile; } public void setMobile(String mobile) { this.mobile = mobile; } @Override public String toString() { return JSONObject.fromObject(this).toString(); } } package serial; import java.io.EOFException; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; public class SerializeUtils { public static void serialize(String fileName, Object o) { ObjectOutputStream oos = null; try { oos = new ObjectOutputStream(new FileOutputStream(fileName)); oos.writeObject(o); oos.close(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } @SuppressWarnings("unchecked") public static <T> T deserialize(String fileName) { Object o = null; ObjectInputStream ois = null; try { ois = new ObjectInputStream(new FileInputStream(fileName)); o = ois.readObject(); ois.close(); } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (EOFException e) { // TODO: handle exception } catch (IOException e) { e.printStackTrace(); } return (T) o; } } package serial; import org.junit.Test; /** * @author blmcz * */ public class SerializeTest { private static final String fileName = "F:\\Develop\\Projects\\Test\\src\\serial\\data\\student.data"; // @Test public void write() { Person p1 = new Person(); p1.setName("bmlcz"); p1.setMobile("1866593XXXX"); p1.setSex("男"); p1.setBirthday("1985-10-08"); SerializeUtils.serialize(fileName, p1); } @Test public void read() { Person p2 = SerializeUtils.deserialize(fileName); System.out.println(p2); } }

例子中，通过write方法将person对象写入student.data文件，再通过read方法读出。我们稍微修改Person.java文件，如加入一个clazz字段后，再通过read方法，读取原来的student.data文件，程序抛出异常：

java.io.InvalidClassException: serial.Person; local class incompatible: stream classdesc serialVersionUID = -3920900594626140766, local class serialVersionUID = -5700869362952204388 at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:617) at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1622) at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1517) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1771) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350) at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370) at serial.SerializeUtils.deserialize(SerializeUtils.java:32) at serial.SerializeTest.read(SerializeTest.java:25) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

我们把Person对象serialVersionUID注释打开，再执行read方法，运行结果如下：

{"birthday":"1985-10-08","clazz":"","mobile":"1866593XXXX","name":"","sex":"男"}

可以看到程序正常执行，并且读出的clazz字段为空。反序列后的时候，新类中新增的字段将被赋以默认值，去掉的字段将被忽略。