How to implement auto suggest using Lucene's n

Question

I am a greenhand on Lucene, and I want to implement auto suggest, just like google, when I input a character like 'G', it would give me a list, you can try your self.

I have searched on the whole net. Nobody has done this , and it gives us some new tools in package suggest

But i need an example to tell me how to do that

Is there anyone can help ?

Answer 1

I'll give you a pretty complete example that shows you how to use AnalyzingInfixSuggester. In this example we'll pretend that we're Amazon, and we want to autocomplete a product search field. We'll take advantage of features of the Lucene suggestion system to implement the following:

1. Ranked results: We will suggest the most popular matching products first.
2. Region-restricted results: We will only suggest products that we sell in the customer's country.
3. Product photos: We will store product photo URLs in the suggestion index so we can display them in the search results, without having to do an additional database lookup.

First I'll define a simple class to hold information about a product in Product.java:

import java.util.Set;

class Product implements java.io.Serializable
{
    String name;
    String image;
    String[] regions;
    int numberSold;

    public Product(String name, String image, String[] regions,
                   int numberSold) {
        this.name = name;
        this.image = image;
        this.regions = regions;
        this.numberSold = numberSold;
    }
}

To index records in with the AnalyzingInfixSuggester's build method you need to pass it an object that implements the org.apache.lucene.search.suggest.InputIterator interface. An InputIterator gives access to the key, contexts, payload and weight for each record.

The key is the text you actually want to search on and autocomplete against. In our example, it will be the name of the product.

The contexts are a set of additional, arbitrary data that you can use to filter records against. In our example, the contexts are the set of ISO codes for the countries we will ship a particular product to.

The payload is additional arbitrary data you want to store in the index for the record. In this example, we will actually serialize each Product instance and store the resulting bytes as the payload. Then when we later do lookups, we can deserialize the payload and access information in the product instance like the image URL.

The weight is used to order suggestion results; results with a higher weight are returned first. We'll use the number of sales for a given product as its weight.

Here's the contents of ProductIterator.java:

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.UnsupportedEncodingException;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import org.apache.lucene.search.suggest.InputIterator;
import org.apache.lucene.util.BytesRef;


class ProductIterator implements InputIterator
{
    private Iterator<Product> productIterator;
    private Product currentProduct;

    ProductIterator(Iterator<Product> productIterator) {
        this.productIterator = productIterator;
    }

    public boolean hasContexts() {
        return true;
    }

    public boolean hasPayloads() {
        return true;
    }

    public Comparator<BytesRef> getComparator() {
        return null;
    }

    // This method needs to return the key for the record; this is the
    // text we'll be autocompleting against.
    public BytesRef next() {
        if (productIterator.hasNext()) {
            currentProduct = productIterator.next();
            try {
                return new BytesRef(currentProduct.name.getBytes("UTF8"));
            } catch (UnsupportedEncodingException e) {
                throw new Error("Couldn't convert to UTF-8");
            }
        } else {
            return null;
        }
    }

    // This method returns the payload for the record, which is
    // additional data that can be associated with a record and
    // returned when we do suggestion lookups.  In this example the
    // payload is a serialized Java object representing our product.
    public BytesRef payload() {
        try {
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            ObjectOutputStream out = new ObjectOutputStream(bos);
            out.writeObject(currentProduct);
            out.close();
            return new BytesRef(bos.toByteArray());
        } catch (IOException e) {
            throw new Error("Well that's unfortunate.");
        }
    }

    // This method returns the contexts for the record, which we can
    // use to restrict suggestions.  In this example we use the
    // regions in which a product is sold.
    public Set<BytesRef> contexts() {
        try {
            Set<BytesRef> regions = new HashSet();
            for (String region : currentProduct.regions) {
                regions.add(new BytesRef(region.getBytes("UTF8")));
            }
            return regions;
        } catch (UnsupportedEncodingException e) {
            throw new Error("Couldn't convert to UTF-8");
        }
    }

    // This method helps us order our suggestions.  In this example we
    // use the number of products of this type that we've sold.
    public long weight() {
        return currentProduct.numberSold;
    }
}

In our driver program, we will do the following things:

1. Create an index directory in RAM.
2. Create a StandardTokenizer.
3. Create an AnalyzingInfixSuggester using the RAM directory and tokenizer.
4. Index a number of products using ProductIterator.
5. Print the results of some sample lookups.

Here's the driver program, SuggestProducts.java:

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;

import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.search.suggest.analyzing.AnalyzingInfixSuggester;
import org.apache.lucene.search.suggest.Lookup;
import org.apache.lucene.store.RAMDirectory;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.Version;

public class SuggestProducts
{
    // Get suggestions given a prefix and a region.
    private static void lookup(AnalyzingInfixSuggester suggester, String name,
                               String region) {
        try {
            List<Lookup.LookupResult> results;
            HashSet<BytesRef> contexts = new HashSet<BytesRef>();
            contexts.add(new BytesRef(region.getBytes("UTF8")));
            // Do the actual lookup.  We ask for the top 2 results.
            results = suggester.lookup(name, contexts, 2, true, false);
            System.out.println("-- \"" + name + "\" (" + region + "):");
            for (Lookup.LookupResult result : results) {
                System.out.println(result.key);
                Product p = getProduct(result);
                if (p != null) {
                    System.out.println("  image: " + p.image);
                    System.out.println("  # sold: " + p.numberSold);
                }
            }
        } catch (IOException e) {
            System.err.println("Error");
        }
    }

    // Deserialize a Product from a LookupResult payload.
    private static Product getProduct(Lookup.LookupResult result)
    {
        try {
            BytesRef payload = result.payload;
            if (payload != null) {
                ByteArrayInputStream bis = new ByteArrayInputStream(payload.bytes);
                ObjectInputStream in = new ObjectInputStream(bis);
                Product p = (Product) in.readObject();
                return p;
            } else {
                return null;
            }
        } catch (IOException|ClassNotFoundException e) {
            throw new Error("Could not decode payload :(");
        }
    }

    public static void main(String[] args) {
        try {
            RAMDirectory index_dir = new RAMDirectory();
            StandardAnalyzer analyzer = new StandardAnalyzer(Version.LUCENE_48);
            AnalyzingInfixSuggester suggester = new AnalyzingInfixSuggester(
                Version.LUCENE_48, index_dir, analyzer);

            // Create our list of products.
            ArrayList<Product> products = new ArrayList<Product>();
            products.add(
                new Product(
                    "Electric Guitar",
                    "http://images.example/electric-guitar.jpg",
                    new String[]{"US", "CA"},
                    100));
            products.add(
                new Product(
                    "Electric Train",
                    "http://images.example/train.jpg",
                    new String[]{"US", "CA"},
                    100));
            products.add(
                new Product(
                    "Acoustic Guitar",
                    "http://images.example/acoustic-guitar.jpg",
                    new String[]{"US", "ZA"},
                    80));
            products.add(
                new Product(
                    "Guarana Soda",
                    "http://images.example/soda.jpg",
                    new String[]{"ZA", "IE"},
                    130));

            // Index the products with the suggester.
            suggester.build(new ProductIterator(products.iterator()));

            // Do some example lookups.
            lookup(suggester, "Gu", "US");
            lookup(suggester, "Gu", "ZA");
            lookup(suggester, "Gui", "CA");
            lookup(suggester, "Electric guit", "US");
        } catch (IOException e) {
            System.err.println("Error!");
        }
    }
}

And here is the output from the driver program:

-- "Gu" (US):
Electric Guitar
  image: http://images.example/electric-guitar.jpg
  # sold: 100
Acoustic Guitar
  image: http://images.example/acoustic-guitar.jpg
  # sold: 80
-- "Gu" (ZA):
Guarana Soda
  image: http://images.example/soda.jpg
  # sold: 130
Acoustic Guitar
  image: http://images.example/acoustic-guitar.jpg
  # sold: 80
-- "Gui" (CA):
Electric Guitar
  image: http://images.example/electric-guitar.jpg
  # sold: 100
-- "Electric guit" (US):
Electric Guitar
  image: http://images.example/electric-guitar.jpg
  # sold: 100

Appendix

There's a way to avoid writing a full InputIterator that you might find easier. You can write a stub InputIterator that returns null from its next, payload and contexts methods. Pass an instance of it to AnalyzingInfixSuggester's build method:

suggester.build(new ProductIterator(new ArrayList<Product>().iterator()));

Then for each item you want to index, call the AnalyzingInfixSuggester add method:

suggester.add(text, contexts, weight, payload)

After you've indexed everything, call refresh:

suggester.refresh();

If you're indexing large amounts of data, it's possible to significantly speedup indexing using this method with multiple threads: Call build, then use multiple threads to add items, then finally call refresh.

[Edited 2015-04-23 to demonstrate deserializing info from the LookupResult payload.]