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## org.modeshape.graph.property
Class PathExpression

    java.lang.Object
      org.modeshape.graph.property.PathExpression

All Implemented Interfaces:
  Serializable

    @Immutable
    public class PathExpression

extends Object
implements Serializable

An expression that defines an acceptable path using a regular-expression-like language. Path expressions can be used to represent node paths or properties.

Let's first look at some simple examples of path expressions:

Path expression | Description
--- | ---
/a/b | Match node "`b`" that is a child of the top level node "`a`". Neither node may have any same-name-sibilings.
/a/* | Match any child node of the top level node "`a`".
/a/*.txt | Match any child node of the top level node "`a`" that also has a name ending in "`.txt`".
/a/b@c | Match the property "`c`" of node "`/a/b`".
/a/b[2] | The second child named "`b`" below the top level node "`a`".
/a/b[2,3,4] | The second, third or fourth child named "`b`" below the top level node "`a`".
/a/b[*] | Any (and every) child named "`b`" below the top level node "`a`".
//a/b | Any node named "`b`" that exists below a node named "`a`", regardless of where node "`a`" occurs. Again, neither node may have any same-name-sibilings.

With these simple examples, you can probably discern the most important rules. First, the '`*`' is a wildcard character that matches any character or sequence of characters in a node's name (or index if appearing in between square brackets), and can be used in conjunction with other characters (e.g., "`*.txt`").

Second, square brackets (i.e., '`[`' and '`]`') are used to match a node's same-name-sibiling index. You can put a single non-negative number or a comma-separated list of non-negative numbers. Use '0' to match a node that has no same-name-sibilings, or any positive number to match the specific same-name-sibling.

Third, combining two delimiters (e.g., "`//`") matches any sequence of nodes, regardless of what their names are or how many nodes. Often used with other patterns to identify nodes at any level matching other patterns. Three or more sequential slash characters are treated as two.

Many path expressions can be created using just these simple rules. However, input paths can be more complicated. Here are some more examples:

Path expressions | Description
--- | ---
/a/(b|c|d) | Match children of the top level node "`a`" that are named "`a`", "`b`" or "`c` ". None of the nodes may have same-name-sibling indexes.
/a/b[c/d] | Match node "`b`" child of the top level node "`a`", when node "`b`" has a child named " `c`", and "`c`" has a child named "`d`". Node "`b` " is the selected node, while nodes "`b`" and "`b`" are used as criteria but are not selected.
/a(/(b|c|d|)/e)[f/g/@something] | Match node "`/a/b/e`", "`/a/c/e`", "`/a/d/e`", or "`/a/e` " when they also have a child "`f`" that itself has a child "`g`" with property "`something`". None of the nodes may have same-name-sibling indexes.

These examples show a few more advanced rules. Parentheses (i.e., '`(`' and '`)`') can be used to define a set of options for names, as shown in the first and third rules. Whatever part of the selected node's path appears between the parentheses is captured for use within the output path. Thus, the first input path in the previous table would match node " `/a/b`", and "b" would be captured and could be used within the output path using "`$1`", where the number used in the output path identifies the parentheses.

Square brackets can also be used to specify criteria on a node's properties or children. Whatever appears in between the square brackets does not appear in the selected node.

### Repository and Workspace names

Path expressions can also specify restrictions on the repository name and workspace name, to constrain the path expression to matching only paths from workspaces in repositories meeting the name criteria. Of course, if the path expression doesn't include these restrictions, the repository and workspace names are not considered when matching paths.

See Also:
  Serialized Form

Nested Class Summary
`static class` | `PathExpression.Matcher`
`static class` | `PathExpression.RepositoryPath`

Constructor Summary
`PathExpression(String expression)` Create the supplied expression.

Method Summary
`static PathExpression` | `all()`
`static PathExpression` | `compile(String expression)` Compile the supplied expression and return the resulting path expression instance.
`boolean` | `equals(Object obj)`
`String` | `getExpression()`
`String` | `getSelectExpression()`
`int` | `hashCode()`
`PathExpression.Matcher` | `matcher(String absolutePath)` Obtain a Matcher that can be used to convert the supplied absolute path (with repository name and workspace name) into an output repository, and output workspace name, and output path.
`boolean` | `matchesAnything()` Return whether this expression matches anything and therefore is not restrictive.
`static PathExpression.RepositoryPath` | `parseRepositoryPath(String path)` Parse a path of the form `{repoName}:{workspaceName}:{absolutePath}` or `{absolutePath}`.
`protected String` | `removeAllPredicatesExceptIndexes(String expression)` Remove all XPath predicates from the supplied regular expression string.
`protected String` | `removeUnusedPredicates(String expression)` Replace certain XPath patterns that are not used or understood.
`protected String` | `replaceXPathPatterns(String expression)` Replace certain XPath patterns, including some predicates, with substrings that are compatible with regular expressions.
`String` | `toString()`

Methods inherited from class java.lang.Object
`clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

Constructor Detail

### PathExpression

    public PathExpression(String expression)
                   throws InvalidPathExpressionException

  Create the supplied expression.

  Parameters:
    `expression` - the expression
  Throws:
    `IllegalArgumentException` - if the expression is null
    `InvalidPathExpressionException` - if the expression is blank or is not a valid expression

Method Detail

### compile

    public static final PathExpression compile(String expression)
                                        throws InvalidPathExpressionException

  Compile the supplied expression and return the resulting path expression instance.

  Parameters:
    `expression` - the expression
  Returns:
    the path expression; never null
  Throws:
    `IllegalArgumentException` - if the expression is null
    `InvalidPathExpressionException` - if the expression is blank or is not a valid expression

### getExpression

    public String getExpression()

  Returns:
    expression

### removeUnusedPredicates

    protected String removeUnusedPredicates(String expression)

  Replace certain XPath patterns that are not used or understood.

  Parameters:
    `expression` - the input regular expressions string; may not be null
  Returns:
    the regular expression with all unused XPath patterns removed; never null

### removeAllPredicatesExceptIndexes

    protected String removeAllPredicatesExceptIndexes(String expression)

  Remove all XPath predicates from the supplied regular expression string.

  Parameters:
    `expression` - the input regular expressions string; may not be null
  Returns:
    the regular expression with all XPath predicates removed; never null

### replaceXPathPatterns

    protected String replaceXPathPatterns(String expression)

  Replace certain XPath patterns, including some predicates, with substrings that are compatible with regular expressions.

  Parameters:
    `expression` - the input regular expressions string; may not be null
  Returns:
    the regular expression with XPath patterns replaced with regular expression fragments; never null

### getSelectExpression

    public String getSelectExpression()

  Returns:
    the expression

### hashCode

    public int hashCode()

  Overrides:
    `hashCode` in class `Object`

### equals

    public boolean equals(Object obj)

  Overrides:
    `equals` in class `Object`

### toString

    public String toString()

  Overrides:
    `toString` in class `Object`

### matcher

    public PathExpression.Matcher matcher(String absolutePath)

  Obtain a Matcher that can be used to convert the supplied absolute path (with repository name and workspace name) into an output repository, and output workspace name, and output path.

  Parameters:
    `absolutePath` - the path, of the form `{repoName}:{workspaceName}:{absPath}`, where `{repoName}:{workspaceName}:` is optional
  Returns:
    the matcher; never null

### matchesAnything

    public boolean matchesAnything()

  Return whether this expression matches anything and therefore is not restrictive. These include expressions of any nodes (" `/`"), any sequence of nodes ("`//`"), the self reference ("`.`"), or wildcard (" `*`", "`*[]`" or "`*[*]`"). Combinations of these individual expressions are also considered to match anything.

  Returns:
    true if the expression matches anything, or false otherwise

### all

    public static PathExpression all()

### parseRepositoryPath

    public static PathExpression.RepositoryPath parseRepositoryPath(String path)

  Parse a path of the form `{repoName}:{workspaceName}:{absolutePath}` or `{absolutePath}`.

  Parameters:
    `path` - the path
  Returns:
    the repository path, or null if the supplied path doesn't match any of the path patterns

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