DefaultExpressionEngine (Apache Commons Configuration 1.10 API)

java.lang.Object
- org.apache.commons.configuration.tree.DefaultExpressionEngine

All Implemented Interfaces:

ExpressionEngine
```
public class DefaultExpressionEngine
extends Object
implements ExpressionEngine
```
A default implementation of the ExpressionEngine interface providing the "native"e; expression language for hierarchical configurations.

This class implements a rather simple expression language for navigating through a hierarchy of configuration nodes. It supports the following operations:
- Navigating from a node to one of its children using the child node delimiter, which is by the default a dot (".").
- Navigating from a node to one of its attributes using the attribute node delimiter, which by default follows the XPATH like syntax [@<attributeName>].
- If there are multiple child or attribute nodes with the same name, a specific node can be selected using a numerical index. By default indices are written in parenthesis.
As an example consider the following XML document:
```
  <database>
    <tables>
      <table type="system">
        <name>users</name>
        <fields>
          <field>
            <name>lid</name>
            <type>long</name>
          </field>
          <field>
            <name>usrName</name>
            <type>java.lang.String</type>
          </field>
         ...
        </fields>
      </table>
      <table>
        <name>documents</name>
        <fields>
          <field>
            <name>docid</name>
            <type>long</type>
          </field>
          ...
        </fields>
      </table>
      ...
    </tables>
  </database>
 
```
If this document is parsed and stored in a hierarchical configuration object, for instance the key tables.table(0).name can be used to find out the name of the first table. In opposite tables.table.name would return a collection with the names of all available tables. Similarly the key tables.table(1).fields.field.name returns a collection with the names of all fields of the second table. If another index is added after the field element, a single field can be accessed: tables.table(1).fields.field(0).name. The key tables.table(0)[@type] would select the type attribute of the first table.

This example works with the default values for delimiters and index markers. It is also possible to set custom values for these properties so that you can adapt a DefaultExpressionEngine to your personal needs.
Since:

1.3

Version:

$Id: DefaultExpressionEngine.java 1301991 2012-03-17 20:18:02Z sebb $

Author:

Commons Configuration team

Field Summary

Fields
Modifier and Type	Field and Description
`static String`	`DEFAULT_ATTRIBUTE_END` Constant for the default attribute end marker.
`static String`	`DEFAULT_ATTRIBUTE_START` Constant for the default attribute start marker.
`static String`	`DEFAULT_ESCAPED_DELIMITER` Constant for the default escaped property delimiter.
`static String`	`DEFAULT_INDEX_END` Constant for the default index end marker.
`static String`	`DEFAULT_INDEX_START` Constant for the default index start marker.
`static String`	`DEFAULT_PROPERTY_DELIMITER` Constant for the default property delimiter.

Constructor Summary

Constructors
Constructor and Description

DefaultExpressionEngine()

Constructors
Constructor and Description
`DefaultExpressionEngine()`

Method Summary

Methods
Modifier and Type	Method and Description
`protected ConfigurationNode`	`findLastPathNode(DefaultConfigurationKey.KeyIterator keyIt, ConfigurationNode node)` Finds the last existing node for an add operation.
`protected void`	`findNodesForKey(DefaultConfigurationKey.KeyIterator keyPart, ConfigurationNode node, Collection<ConfigurationNode> nodes)` Recursive helper method for evaluating a key.
`String`	`getAttributeEnd()` Sets the attribute end marker.
`String`	`getAttributeStart()` Returns the attribute start marker.
`String`	`getEscapedDelimiter()` Returns the escaped property delimiter string.
`String`	`getIndexEnd()` Returns the index end marker.
`String`	`getIndexStart()` Returns the index start marker.
`String`	`getPropertyDelimiter()` Returns the property delimiter.
`String`	`nodeKey(ConfigurationNode node, String parentKey)` Determines the key of the passed in node.
`NodeAddData`	`prepareAdd(ConfigurationNode root, String key)` Prepares Adding the property with the specified key.
`List<ConfigurationNode>`	`query(ConfigurationNode root, String key)` Evaluates the given key and returns all matching nodes.
`void`	`setAttributeEnd(String attributeEnd)` Sets the attribute end marker.
`void`	`setAttributeStart(String attributeStart)` Sets the attribute start marker.
`void`	`setEscapedDelimiter(String escapedDelimiter)` Sets the escaped property delimiter string.
`void`	`setIndexEnd(String indexEnd)` Sets the index end marker.
`void`	`setIndexStart(String indexStart)` Sets the index start marker.
`void`	`setPropertyDelimiter(String propertyDelimiter)` Sets the property delimiter.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - DEFAULT_PROPERTY_DELIMITER
```
public static final String DEFAULT_PROPERTY_DELIMITER
```
    Constant for the default property delimiter.
    
    See Also:
    Constant Field Values
  - DEFAULT_ESCAPED_DELIMITER
```
public static final String DEFAULT_ESCAPED_DELIMITER
```
    Constant for the default escaped property delimiter.
    
    See Also:
    Constant Field Values
  - DEFAULT_ATTRIBUTE_START
```
public static final String DEFAULT_ATTRIBUTE_START
```
    Constant for the default attribute start marker.
    
    See Also:
    Constant Field Values
  - DEFAULT_ATTRIBUTE_END
```
public static final String DEFAULT_ATTRIBUTE_END
```
    Constant for the default attribute end marker.
    
    See Also:
    Constant Field Values
  - DEFAULT_INDEX_START
```
public static final String DEFAULT_INDEX_START
```
    Constant for the default index start marker.
    
    See Also:
    Constant Field Values
  - DEFAULT_INDEX_END
```
public static final String DEFAULT_INDEX_END
```
    Constant for the default index end marker.
    
    See Also:
    Constant Field Values
- Constructor Detail
  - DefaultExpressionEngine
```
public DefaultExpressionEngine()
```
- Method Detail
  - getAttributeEnd
```
public String getAttributeEnd()
```
    Sets the attribute end marker.
    
    Returns:
    the attribute end marker
  - setAttributeEnd
```
public void setAttributeEnd(String attributeEnd)
```
    Sets the attribute end marker.
    
    Parameters:
    attributeEnd - the attribute end marker; can be null if no end marker is needed
  - getAttributeStart
```
public String getAttributeStart()
```
    Returns the attribute start marker.
    
    Returns:
    the attribute start marker
  - setAttributeStart
```
public void setAttributeStart(String attributeStart)
```
    Sets the attribute start marker. Attribute start and end marker are used together to detect attributes in a property key.
    
    Parameters:
    attributeStart - the attribute start marker
  - getEscapedDelimiter
```
public String getEscapedDelimiter()
```
    Returns the escaped property delimiter string.
    
    Returns:
    the escaped property delimiter
  - setEscapedDelimiter
```
public void setEscapedDelimiter(String escapedDelimiter)
```
    Sets the escaped property delimiter string. With this string a delimiter that belongs to the key of a property can be escaped. If for instance "." is used as property delimiter, you can set the escaped delimiter to "\." and can then escape the delimiter with a back slash.
    
    Parameters:
    escapedDelimiter - the escaped delimiter string
  - getIndexEnd
```
public String getIndexEnd()
```
    Returns the index end marker.
    
    Returns:
    the index end marker
  - setIndexEnd
```
public void setIndexEnd(String indexEnd)
```
    Sets the index end marker.
    
    Parameters:
    indexEnd - the index end marker
  - getIndexStart
```
public String getIndexStart()
```
    Returns the index start marker.
    
    Returns:
    the index start marker
  - setIndexStart
```
public void setIndexStart(String indexStart)
```
    Sets the index start marker. Index start and end marker are used together to detect indices in a property key.
    
    Parameters:
    indexStart - the index start marker
  - getPropertyDelimiter
```
public String getPropertyDelimiter()
```
    Returns the property delimiter.
    
    Returns:
    the property delimiter
  - setPropertyDelimiter
```
public void setPropertyDelimiter(String propertyDelimiter)
```
    Sets the property delimiter. This string is used to split the parts of a property key.
    
    Parameters:
    propertyDelimiter - the property delimiter
  - query
```
public List<ConfigurationNode> query(ConfigurationNode root,
                            String key)
```
    Evaluates the given key and returns all matching nodes. This method supports the syntax as described in the class comment.
    
    Specified by:
    
    query in interface ExpressionEngine
    
    Parameters:
    root - the root node
    key - the key
    
    Returns:
    a list with the matching nodes
  - nodeKey
```
public String nodeKey(ConfigurationNode node,
             String parentKey)
```
    Determines the key of the passed in node. This implementation takes the given parent key, adds a property delimiter, and then adds the node's name. (For attribute nodes the attribute delimiters are used instead.) The name of the root node is a blanc string. Note that no indices will be returned.
    
    Specified by:
    
    nodeKey in interface ExpressionEngine
    
    Parameters:
    node - the node whose key is to be determined
    parentKey - the key of this node's parent
    
    Returns:
    the key for the given node
  - prepareAdd
```
public NodeAddData prepareAdd(ConfigurationNode root,
                     String key)
```
    Prepares Adding the property with the specified key.
    
    To be able to deal with the structure supported by hierarchical configuration implementations the passed in key is of importance, especially the indices it might contain. The following example should clarify this: Suppose the actual node structure looks like the following:
```
  tables
     +-- table
             +-- name = user
             +-- fields
                     +-- field
                             +-- name = uid
                     +-- field
                             +-- name = firstName
                     ...
     +-- table
             +-- name = documents
             +-- fields
                    ...
 
```
    In this example a database structure is defined, e.g. all fields of the first table could be accessed using the key tables.table(0).fields.field.name. If now properties are to be added, it must be exactly specified at which position in the hierarchy the new property is to be inserted. So to add a new field name to a table it is not enough to say just
```
 config.addProperty("tables.table.fields.field.name", "newField");
 
```
    The statement given above contains some ambiguity. For instance it is not clear, to which table the new field should be added. If this method finds such an ambiguity, it is resolved by following the last valid path. Here this would be the last table. The same is true for the field; because there are multiple fields and no explicit index is provided, a new name property would be added to the last field - which is probably not what was desired.
    
    To make things clear explicit indices should be provided whenever possible. In the example above the exact table could be specified by providing an index for the table element as in tables.table(1).fields. By specifying an index it can also be expressed that at a given position in the configuration tree a new branch should be added. In the example above we did not want to add an additional name element to the last field of the table, but we want a complete new field element. This can be achieved by specifying an invalid index (like -1) after the element where a new branch should be created. Given this our example would run:
```
 config.addProperty("tables.table(1).fields.field(-1).name", "newField");
 
```
    With this notation it is possible to add new branches everywhere. We could for instance create a new table element by specifying
```
 config.addProperty("tables.table(-1).fields.field.name", "newField2");
 
```
    (Note that because after the table element a new branch is created indices in following elements are not relevant; the branch is new so there cannot be any ambiguities.)
    Specified by:
    
    prepareAdd in interface ExpressionEngine
    
    Parameters:
    root - the root node of the nodes hierarchy
    key - the key of the new property
    
    Returns:
    a data object with information needed for the add operation
  - findNodesForKey
```
protected void findNodesForKey(DefaultConfigurationKey.KeyIterator keyPart,
                   ConfigurationNode node,
                   Collection<ConfigurationNode> nodes)
```
    Recursive helper method for evaluating a key. This method processes all facets of a configuration key, traverses the tree of properties and fetches the the nodes of all matching properties.
    
    Parameters:
    keyPart - the configuration key iterator
    node - the actual node
    nodes - here the found nodes are stored
  - findLastPathNode
```
protected ConfigurationNode findLastPathNode(DefaultConfigurationKey.KeyIterator keyIt,
                                 ConfigurationNode node)
```
    Finds the last existing node for an add operation. This method traverses the configuration node tree along the specified key. The last existing node on this path is returned.
    
    Parameters:
    keyIt - the key iterator
    node - the actual node
    
    Returns:
    the last existing node on the given path

Class DefaultExpressionEngine

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

DEFAULT_PROPERTY_DELIMITER

DEFAULT_ESCAPED_DELIMITER

DEFAULT_ATTRIBUTE_START

DEFAULT_ATTRIBUTE_END

DEFAULT_INDEX_START

DEFAULT_INDEX_END

Constructor Detail

DefaultExpressionEngine

Method Detail

getAttributeEnd

setAttributeEnd

getAttributeStart

setAttributeStart

getEscapedDelimiter

setEscapedDelimiter

getIndexEnd

setIndexEnd

getIndexStart

setIndexStart

getPropertyDelimiter

setPropertyDelimiter

query

nodeKey

prepareAdd

findNodesForKey

findLastPathNode