Java – Troubleshoot Java Lucene ignoring Field

javalucene

We're currently using Lucene 2.1.0 for our site search and we've hit a difficult problem: one of our index fields is being ignored during a targeted search. Here is the code for adding the field to a document in our index:

// Add market_local to index
contactDocument.add(
    new Field(
        "market_local"
        , StringUtils.objectToString(
            currClip.get(
                "market_local"
            )
        )
        , Field.Store.YES
        , Field.Index.UN_TOKENIZED 
    )
);

Running a query ( * ) against the index will return the following results:

Result 1:
    title: Foo Bar
    market_local: Local

Result 2:
    title: Bar Foo
    market_local: National

Running a targeted query:

+( market_local:Local )

won't find any results.

I realize this is a highly specific question, I'm just trying to get information on where to start debugging this issue, as I'm a Lucene newbie.

UPDATE

Installed Luke, checking out latest index… the Field market_local is available in searches, so if I execute something like:

market_local:Local

The search works correctly (in Luke). I'm going over our Analyzer code now, is there any way I could chalk this issue up to the fact that our search application is using Lucene 2.1.0 and the latest version of Luke is using 2.3.0?

Best Answer

For debugging Lucene, the best tool to use is Luke, which lets you poke around in the index itself to see what got indexed, carry out searches, etc. I recommend downloading it, pointing it at your index, and seeing what's in there.

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Java – What are the differences between a HashMap and a Hashtable in Java

There are several differences between HashMap and Hashtable in Java:

Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
One of HashMap's subclasses is LinkedHashMap, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the HashMap for a LinkedHashMap. This wouldn't be as easy if you were using Hashtable.

Since synchronization is not an issue for you, I'd recommend HashMap. If synchronization becomes an issue, you may also look at ConcurrentHashMap.

Java – Is Java “pass-by-reference” or “pass-by-value”

Java is always pass-by-value. Unfortunately, when we deal with objects we are really dealing with object-handles called references which are passed-by-value as well. This terminology and semantics easily confuse many beginners.

It goes like this:

public static void main(String[] args) {
    Dog aDog = new Dog("Max");
    Dog oldDog = aDog;

    // we pass the object to foo
    foo(aDog);
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    aDog.getName().equals("Max"); // true
    aDog.getName().equals("Fifi"); // false
    aDog == oldDog; // true
}

public static void foo(Dog d) {
    d.getName().equals("Max"); // true
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}

In the example above aDog.getName() will still return "Max". The value aDog within main is not changed in the function foo with the Dog "Fifi" as the object reference is passed by value. If it were passed by reference, then the aDog.getName() in main would return "Fifi" after the call to foo.

Likewise:

public static void main(String[] args) {
    Dog aDog = new Dog("Max");
    Dog oldDog = aDog;

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}

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}

In the above example, Fifi is the dog's name after call to foo(aDog) because the object's name was set inside of foo(...). Any operations that foo performs on d are such that, for all practical purposes, they are performed on aDog, but it is not possible to change the value of the variable aDog itself.

For more information on pass by reference and pass by value, consult the following SO answer: https://stackoverflow.com/a/430958/6005228. This explains more thoroughly the semantics and history behind the two and also explains why Java and many other modern languages appear to do both in certain cases.

Best Answer

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Java – What are the differences between a HashMap and a Hashtable in Java

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