org.apache.jackrabbit.oak.spi.state.NodeState Maven / Gradle / Ivy
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* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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* See the License for the specific language governing permissions and
* limitations under the License.
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package org.apache.jackrabbit.oak.spi.state;
import javax.annotation.CheckForNull;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import org.apache.jackrabbit.oak.api.PropertyState;
import com.google.common.base.Predicate;
/**
* A node in a content tree consists of child nodes and properties, each
* of which evolves through different states during its lifecycle. This
* interface represents a specific, immutable state of a node.
*
* The state of a node consists of named properties and child nodes. Names
* are non-empty strings that never contain the forward slash character, "/".
* Implementations may place additional restrictions on possible name strings.
* The properties and child nodes are unordered, and no two properties or
* two child nodes may have the same name. An implementation may additionally
* restrict a property and a child node from having the same name.
*
* Depending on context, a NodeState instance can be interpreted as
* representing the state of just that node, of the subtree starting at
* that node, or of an entire tree in case it's a root node.
*
* The crucial difference between this interface and the similarly named
* class in Jackrabbit 2.x is that this interface represents a specific,
* immutable state of a node, whereas the Jackrabbit 2.x class represented
* the current state of a node.
*
*
Immutability and thread-safety
*
* As mentioned above, all node and property states are always immutable.
* Thus repeating a method call is always guaranteed to produce the same
* result as before unless some internal error occurs (see below). This
* immutability only applies to a specific state instance. Different states
* of a node can obviously be different, and in some cases even different
* instances of the same state may behave slightly differently. For example
* due to performance optimization or other similar changes the iteration
* order of properties or child nodes may be different for two instances
* of the same state.
*
* In addition to being immutable, a specific state instance is guaranteed to
* be fully thread-safe. Possible caching or other internal changes need to
* be properly synchronized so that any number of concurrent clients can
* safely access a state instance.
*
*
Persistence and error-handling
*
* A node state can be (and often is) backed by local files or network
* resources. All IO operations or related concerns like caching should be
* handled transparently below this interface. Potential IO problems and
* recovery attempts like retrying a timed-out network access need to be
* handled below this interface, and only hard errors should be thrown up
* as {@link RuntimeException unchecked exceptions} that higher level code
* is not expected to be able to recover from.
*
* Since this interface exposes no higher level constructs like locking,
* node types or even path parsing, there's no way for content access to
* fail because of such concerns. Such functionality and related checked
* exceptions or other control flow constructs should be implemented on
* a higher level above this interface. On the other hand read access
* controls can be implemented below this interface, in which
* case some content that would otherwise be accessible might not show
* up through such an implementation.
*
*
Existence and iterability of node states
*
* The {@link #getChildNode(String)} method is special in that it
* never returns a {@code null} value, even if the named child
* node does not exist. Instead a client should use the {@link #exists()}
* method on the returned child state to check whether that node exists.
* The purpose of this separation of concerns is to allow an implementation
* to lazily load content only when it's actually read instead of just
* traversed. It also simplifies client code by avoiding the need for many
* {@code null} checks when traversing paths.
*
* The iterability of a node is a related concept to the
* above-mentioned existence. A node state is iterable if it
* is included in the return values of the {@link #getChildNodeCount(long)},
* {@link #getChildNodeNames()} and {@link #getChildNodeEntries()} methods.
* An iterable node is guaranteed to exist, though not all existing nodes
* are necessarily iterable.
*
* Furthermore, a non-existing node is guaranteed to contain no properties
* or iterable child nodes. It can, however contain non-iterable children.
* Such scenarios are typically the result of access control restrictions.
*
*
Decoration and virtual content
*
* Not all content exposed by this interface needs to be backed by actual
* persisted data. An implementation may want to provide derived data,
* like for example the aggregate size of the entire subtree as an
* extra virtual property. A virtualization, sharding or caching layer
* could provide a composite view over multiple underlying trees.
* Or a an access control layer could decide to hide certain content
* based on specific rules. All such features need to be implemented
* according to the API contract of this interface. A separate higher level
* interface needs to be used if an implementation can't for example
* guarantee immutability of exposed content as discussed above.
*
*
Equality and hash codes
*
* Two node states are considered equal if and only if their existence,
* properties and iterable child nodes match, regardless of ordering. The
* {@link Object#equals(Object)} method needs to be implemented so that it
* complies with this definition. And while node states are not meant for
* use as hash keys, the {@link Object#hashCode()} method should still be
* implemented according to this equality contract.
*/
public interface NodeState {
/**
* Checks whether this node exists. See the above discussion about
* the existence of node states.
*
* @return {@code true} if this node exists, {@code false} if not
*/
boolean exists();
/**
* Checks whether the named property exists. The implementation is
* equivalent to {@code getProperty(name) != null}, but may be optimized
* to avoid having to load the property value.
*
* @param name property name
* @return {@code true} if the named property exists,
* {@code false} otherwise
*/
boolean hasProperty(@Nonnull String name);
/**
* Returns the named property, or {@code null} if no such property exists.
*
* @param name name of the property to return
* @return named property, or {@code null} if not found
*/
@CheckForNull
PropertyState getProperty(@Nonnull String name);
/**
* Returns the boolean value of the named property. The implementation
* is equivalent to the following code, but may be optimized.
*
* {@code
* PropertyState property = state.getProperty(name);
* return property != null
* && property.getType() == Type.BOOLEAN
* && property.getValue(Type.BOOLEAN);
* }
*
*
* @param name property name
* @return boolean value of the named property, or {@code false}
*/
boolean getBoolean(@Nonnull String name);
/**
* Returns the long value of the named property. The implementation
* is equivalent to the following code, but may be optimized.
*
* {@code
* PropertyState property = state.getProperty(name);
* if (property != null && property.getType() == Type.LONG) {
* return property.getValue(Type.LONG);
* } else {
* return 0;
* }
* }
*
*
* @param name property name
* @return long value of the named property, or zero
*/
long getLong(String name);
/**
* Returns the string value of the named property. The implementation
* is equivalent to the following code, but may be optimized.
*
* {@code
* PropertyState property = state.getProperty(name);
* if (property != null && property.getType() == Type.STRING) {
* return property.getValue(Type.STRING);
* } else {
* return null;
* }
* }
*
*
* @param name property name
* @return string value of the named property, or {@code null}
*/
@CheckForNull
String getString(String name);
/**
* Returns the string values of the named property. The implementation
* is equivalent to the following code, but may be optimized.
*
* {@code
* PropertyState property = state.getProperty(name);
* if (property != null && property.getType() == Type.STRINGS) {
* return property.getValue(Type.STRINGS);
* } else {
* return Collections.emptyList();
* }
* }
*
*
* @param name property name
* @return string values of the named property, or an empty collection
*/
@Nonnull
Iterable getStrings(@Nonnull String name);
/**
* Returns the name value of the named property. The implementation
* is equivalent to the following code, but may be optimized.
*
* {@code
* PropertyState property = state.getProperty(name);
* if (property != null && property.getType() == Type.NAME) {
* return property.getValue(Type.NAME);
* } else {
* return null;
* }
* }
*
*
* @param name property name
* @return name value of the named property, or {@code null}
*/
@CheckForNull
String getName(@Nonnull String name);
/**
* Returns the name values of the named property. The implementation
* is equivalent to the following code, but may be optimized.
*
* {@code
* PropertyState property = state.getProperty(name);
* if (property != null && property.getType() == Type.NAMES) {
* return property.getValue(Type.NAMES);
* } else {
* return Collections.emptyList();
* }
* }
*
*
* @param name property name
* @return name values of the named property, or an empty collection
*/
@Nonnull
Iterable getNames(@Nonnull String name);
/**
* Returns the number of properties of this node.
*
* @return number of properties
*/
long getPropertyCount();
/**
* Returns an iterable of the properties of this node. Multiple
* iterations are guaranteed to return the properties in the same
* order, but the specific order used is implementation-dependent
* and may change across different states of the same node.
*
* @return properties in some stable order
*/
@Nonnull
Iterable getProperties();
/**
* Checks whether the named child node exists. The implementation
* is equivalent to {@code getChildNode(name).exists()}, except that
* passing an invalid name as argument will result in a {@code false}
* return value instead of an {@link IllegalArgumentException}.
*
* @param name name of the child node
* @return {@code true} if the named child node exists,
* {@code false} otherwise
*/
boolean hasChildNode(@Nonnull String name);
/**
* Returns the named, possibly non-existent, child node. Use the
* {@link #exists()} method on the returned child node to determine
* whether the node exists or not.
*
* @param name name of the child node to return
* @return named child node
* @throws IllegalArgumentException if the given name string is is empty
* or contains a forward slash character
*/
@Nonnull
NodeState getChildNode(@Nonnull String name) throws IllegalArgumentException;
/**
* Returns the number of iterable child nodes of this node.
*
* If an implementation knows the exact value, it returns it (even if
* the value is higher than max). If the implementation does not know the
* exact value, and the child node count is higher than max, it may return
* Long.MAX_VALUE. The cost of the operation is at most O(max).
*
* @param max the maximum number of entries to traverse
* @return number of iterable child nodes
*/
long getChildNodeCount(long max);
/**
* Returns the names of all iterable child nodes.
*
* @return child node names in some stable order
*/
Iterable getChildNodeNames();
/**
* Returns the iterable child node entries of this instance.
* Multiple iterations are guaranteed to return the child nodes in
* the same order, but the specific order used is implementation
* dependent and may change across different states of the same node.
*
* Note on cost and performance: while it is possible to iterate over
* all child {@code NodeState}s with the two methods {@link
* #getChildNodeNames()} and {@link #getChildNode(String)}, this method is
* considered more efficient because an implementation can potentially
* perform the retrieval of the name and {@code NodeState} in one call.
* This results in O(n) vs. O(n log n) when iterating over the child node
* names and then look up the {@code NodeState} by name.
*
* @return child node entries in some stable order
*/
@Nonnull
Iterable getChildNodeEntries();
/**
* Returns a builder for constructing a new node state based on
* this state, i.e. starting with all the properties and child nodes
* of this state.
*
* @since Oak 0.6
* @return node builder based on this state
*/
@Nonnull
NodeBuilder builder();
/**
* Compares this node state against the given base state. Any differences
* are reported by calling the relevant added/changed/deleted methods of
* the given handler.
*
* TODO: Define the behavior of this method with regards to
* iterability/existence of child nodes.
*
* @param base base state
* @param diff handler of node state differences
* @return {@code true} if the full diff was performed, or
* {@code false} if it was aborted as requested by the handler
* (see the {@link NodeStateDiff} contract for more details)
* @since 0ak 0.4, return value added in 0.7
*/
boolean compareAgainstBaseState(NodeState base, NodeStateDiff diff);
/**
* Predicate that checks the existence of NodeState instances.
*/
Predicate EXISTS = new Predicate() {
@Override
public boolean apply(@Nullable NodeState input) {
return input != null && input.exists();
}
};
}