java-design-patterns/tolerant-reader/src/main/java/com/iluwatar/tolerantreader/App.java

package com.iluwatar.tolerantreader;

import java.io.IOException;

/**
 * 
 * Tolerant Reader is an integration pattern that helps creating robust communication
 * systems. The idea is to be as tolerant as possible when reading data from another
 * service. This way, when the communication schema changes, the readers must not break.
 * <p>
 * In this example we use Java serialization to write representations of {@link RainbowFish}
 * objects to file. {@link RainbowFish} is the initial version which we can easily read and
 * write using {@link RainbowFishSerializer} methods. {@link RainbowFish} then evolves to {@link RainbowFishV2}
 * and we again write it to file with a method designed to do just that. However, the reader
 * client does not know about the new format and still reads with the method designed for
 * V1 schema. Fortunately the reading method has been designed with the Tolerant Reader
 * pattern and does not break even though {@link RainbowFishV2} has new fields that are serialized.
 *
 */
public class App {
	
    public static void main( String[] args ) throws IOException, ClassNotFoundException {
    	// Write V1
    	RainbowFish fishV1 = new RainbowFish("Zed", 10, 11, 12);
    	System.out.println(String.format("fishV1 name=%s age=%d length=%d weight=%d", fishV1.getName(), 
    			fishV1.getAge(), fishV1.getLengthMeters(), fishV1.getWeightTons()));
    	RainbowFishSerializer.writeV1(fishV1, "fish1.out");
    	// Read V1
    	RainbowFish deserializedFishV1 = RainbowFishSerializer.readV1("fish1.out");
    	System.out.println(String.format("deserializedFishV1 name=%s age=%d length=%d weight=%d", deserializedFishV1.getName(), 
    			deserializedFishV1.getAge(), deserializedFishV1.getLengthMeters(), deserializedFishV1.getWeightTons()));
    	// Write V2
    	RainbowFishV2 fishV2 = new RainbowFishV2("Scar", 5, 12, 15, true, true, true);
    	System.out.println(String.format("fishV2 name=%s age=%d length=%d weight=%d sleeping=%b hungry=%b angry=%b", fishV2.getName(), 
    			fishV2.getAge(), fishV2.getLengthMeters(), fishV2.getWeightTons(), fishV2.getHungry(), fishV2.getAngry(), fishV2.getSleeping()));
    	RainbowFishSerializer.writeV2(fishV2, "fish2.out");
    	// Read V2 with V1 method
    	RainbowFish deserializedFishV2 = RainbowFishSerializer.readV1("fish2.out");
    	System.out.println(String.format("deserializedFishV2 name=%s age=%d length=%d weight=%d", deserializedFishV2.getName(), 
    			deserializedFishV2.getAge(), deserializedFishV2.getLengthMeters(), deserializedFishV2.getWeightTons()));
    }
}