Advanced Search

Externalizable Example

/ Published in: Java
Save to your folder(s)
Externalizable interface provides you an alternate to Serializable interface. In Externalizable, you specify how/what to persist.

Seralizable persists all non-transient elements using default serialize/deserialize implementation.

Expand | Embed | Plain Text

Copy this code and paste it in your HTML 
  1. package com.test.jvm;
  2.  
  3. import java.io.Externalizable;
  4. import java.io.FileInputStream;
  5. import java.io.FileOutputStream;
  6. import java.io.IOException;
  7. import java.io.ObjectInput;
  8. import java.io.ObjectInputStream;
  9. import java.io.ObjectOutput;
  10. import java.io.ObjectOutputStream;
  11.  
  12. public class ExternalizableTest {
  13.  
  14. 	public static void main(String[] args) throws IOException, ClassNotFoundException {
  15. 		MyTestObject testObj = new MyTestObject();
  16. 		testObj.setL(12345678L);
  17. 		testObj.setS("hello");
  18.  
  19. 		// Serialize object
  20. 		FileOutputStream fos = new FileOutputStream("obj.ser");
  21. 		ObjectOutputStream oos = new ObjectOutputStream(fos);
  22. 		oos.writeObject(testObj);
  23.  
  24. 		// Deserialize object
  25. 		FileInputStream fis = new FileInputStream("obj.ser");
  26. 		ObjectInputStream ois = new ObjectInputStream(fis);
  27. 		MyTestObject objRead = (MyTestObject)ois.readObject();
  28. 		System.out.println("objRead: s="+objRead.getS()+", l="+objRead.getL());
  29. 	}
  30.  
  31. }
  32.  
  33. class MyTestObject implements Externalizable {
  34. 	private String s;
  35. 	private long l;
  36.  
  37. 	public MyTestObject() {
  38. 	}
  39.  
  40. 	public String getS() {
  41. 		return s;
  42. 	}
  43.  
  44. 	public void setS(String s) {
  45. 		this.s = s;
  46. 	}
  47.  
  48. 	public long getL() {
  49. 		return l;
  50. 	}
  51.  
  52. 	public void setL(long l) {
  53. 		this.l = l;
  54. 	}
  55.  
  56. 	@Override
  57. 	public void writeExternal(ObjectOutput out) throws IOException {
  58. 		out.writeObject(this.s);
  59. 		out.writeLong(this.l);
  60. 		System.out.println("writeExternal complete");
  61. 	}
  62.  
  63. 	@Override
  64. 	public void readExternal(ObjectInput in) throws IOException,
  65. 			ClassNotFoundException {
  66. 		this.s = (String) in.readObject();
  67. 		this.l = in.readLong();
  68. 		System.out.println("readExternal complete");
  69. 	}
  70. }
  71.  
  72.  
  73.  
  74. /*
  75. #1:
  76. Output:
  77. writeExternal complete
  78. readExternal complete
  79. objRead: s=hello, l=12345678
  80.  
  81.  
  82. #2:
  83. If the no-arg constructor of MyTestObject is commented out, you'll get the below error:
  84. Exception in thread "main" java.io.InvalidClassException: com.test.jvm.MyTestObject; com.test.jvm.MyTestObject; no valid constructor
  85. 	at java.io.ObjectStreamClass.checkDeserialize(ObjectStreamClass.java:724)
  86. 	at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1744)
  87. 	at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1340)
  88. 	at java.io.ObjectInputStream.readObject(ObjectInputStream.java:362)
  89. 	at com.test.jvm.ExternalizableTest.main(ExternalizableTest.java:27)
  90. Caused by: java.io.InvalidClassException: com.test.jvm.MyTestObject; no valid constructor
  91. 	at java.io.ObjectStreamClass.<init>(ObjectStreamClass.java:482)
  92. 	at java.io.ObjectStreamClass.lookup(ObjectStreamClass.java:321)
  93. 	at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1117)
  94. 	at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:337)
  95. 	at com.test.jvm.ExternalizableTest.main(ExternalizableTest.java:22)
  96.  
  97. */

URL: http://www.dzone.com/links/r/optimizing_java_serialization_java_vs_xml_vs_json.html

Report this snippet


Comments

RSS Icon Subscribe to comments

You need to login to post a comment.