Design and Architectural Principles - Java 8 Lambdas - page 123

}

}

Example 8-11. Using the zip algorithm to compress data
public public class class ZipCompressionStrategy ZipCompressionStrategy implements implements CompressionStrategy {

@Override
public

public OutputStream compress ( OutputStream data ) throws throws IOException {

return return new new ZipOutputStream ( data );

}

}

Now we can implement our Compressor class, which is the context in which we use our
strategy. This has a compress method on it that takes input and output files and writes a
compressed version of the input file to the output file. It takes the CompressionStrategy as
a constructor parameter that its calling code can use to make a runtime choice as to which
compression strategy to use—for example, getting user input that would make the decision
(see Example 8-12 ) .

Example 8-12. Our compressor is provided with a compression strategy at construction time
public public class class Compressor Compressor {

private private final final CompressionStrategy strategy ;

public public Compressor ( CompressionStrategy strategy ) {

this

this . strategy = strategy ;

}

public public void void compress ( Path inFile , File outFile ) throws throws IOException {

try try ( OutputStream outStream = new new FileOutputStream ( outFile )) {

Files . copy ( inFile , strategy . compress ( outStream ));

}

}
}

If we have a traditional implementation of the strategy pattern, then we can write client code
that creates a new Compressor with whichever strategy we want ( Example 8-13 ) .

Example 8-13. Instantiating the Compressor using concrete strategy classes
Compressor gzipCompressor = new new Compressor ( new new GzipCompressionStrategy ());

gzipCompressor . compress ( inFile , outFile );