# Package org.apache.lucene.queryparser.flexible.core

Core classes of the flexible query parser framework.

See: Description

- Class Summary
  Class | Description
  --- | ---
  QueryParserHelper | This class is a helper for the query parser framework, it does all the three query parser phrases at once: text parsing, query processing and query building.

- Exception Summary
  Exception | Description
  --- | ---
  QueryNodeException | This exception should be thrown if something wrong happens when dealing with `QueryNode`s.
  QueryNodeParseException | This should be thrown when an exception happens during the query parsing from string to the query node tree.

- Error Summary
  Error | Description
  --- | ---
  QueryNodeError | Error class with NLS support

## Package org.apache.lucene.queryparser.flexible.core Description

Core classes of the flexible query parser framework.

## Flexible Query Parser

This package contains the necessary classes to implement a query parser.

A query parser is divided in at least 2 phases, text parsing and query building, and one optional phase called query processing.

### First Phase: Text Parsing

The text parsing phase is performed by a text parser, which implements `SyntaxParser` interface. A text parser is responsible to get a query string and convert it to a `QueryNode` tree, which is an object structure that represents the elements defined in the query string.

### Second (optional) Phase: Query Processing

The query processing phase is performed by a query processor, which implements `QueryNodeProcessor`. A query processor is responsible to perform any processing on a `QueryNode` tree. This phase is optional and is used only if an extra processing, validation, query expansion, etc needs to be performed in a `QueryNode` tree. The `QueryNode` tree can be either be generated by a text parser or programmatically created.

### Third Phase: Query Building

The query building phase is performed by a query builder, which implements `QueryBuilder`. A query builder is responsible to convert a `QueryNode` tree into an arbitrary object, which is usually used to be executed against a search index.

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