reactor.util.context

Interface Context

public interface Context

A key/value store that is propagated between components such as operators via the context protocol. Contexts are ideal to transport orthogonal information such as tracing or security tokens.

Context implementations are thread-safe and immutable: mutative operations like put(Object, Object) will in fact return a new Context instance.

Note that contexts are optimized for low cardinality key/value storage, and a user might want to associate a dedicated mutable structure to a single key to represent his own context instead of using multiple put(java.lang.Object, java.lang.Object), which could be more costly. Past five user key/value pair, the Context will use a copy-on-write implementation backed by a new Map on each put(java.lang.Object, java.lang.Object).

Author:

Stephane Maldini

Method Summary

Modifier and Type	Method and Description
Context	delete(Object key) Return a new Context that will resolve all existing keys except the removed one, key.
static Context	empty() Return an empty Context
default <T> T	get(Class<T> key) Resolve a value given a type key within the Context.
<T> T	get(Object key) Resolve a value given a key that exists within the Context, or throw a NoSuchElementException if the key is not present.
default <T> T	getOrDefault(Object key, T defaultValue) Resolve a value given a key within the Context.
default <T> Optional<T>	getOrEmpty(Object key) Resolve a value given a key within the Context.
boolean	hasKey(Object key) Return true if a particular key resolves to a value within the Context.
default boolean	isEmpty() Return true if the Context is empty.
static Context	of(Map<?,?> map) Create a Context out of a Map.
static Context	of(Object key, Object value) Create a Context pre-initialized with one key-value pair.
static Context	of(Object key1, Object value1, Object key2, Object value2) Create a Context pre-initialized with two key-value pairs.
static Context	of(Object key1, Object value1, Object key2, Object value2, Object key3, Object value3) Create a Context pre-initialized with three key-value pairs.
static Context	of(Object key1, Object value1, Object key2, Object value2, Object key3, Object value3, Object key4, Object value4) Create a Context pre-initialized with four key-value pairs.
static Context	of(Object key1, Object value1, Object key2, Object value2, Object key3, Object value3, Object key4, Object value4, Object key5, Object value5) Create a Context pre-initialized with five key-value pairs.
Context	put(Object key, Object value) Create a new Context that contains all current key/value pairs plus the given key/value pair.
default Context	putAll(Context other) Create a new Context by merging the content of this context and a given Context.
default Context	putNonNull(Object key, Object valueOrNull) Create a new Context that contains all current key/value pairs plus the given key/value pair only if the value is not null.
int	size() Return the size of this Context, the number of immutable key/value pairs stored inside it.
Stream<Map.Entry<Object,Object>>	stream() Stream key/value pairs from this Context

Method Detail

delete

Context delete(Object key)

Return a new Context that will resolve all existing keys except the removed one, key.

Note that if this Context doesn't contain the key, this method simply returns this same instance.

Parameters:

key - the key to remove.

Returns:

a new Context that doesn't include the provided key

empty

static Context empty()

Return an empty Context

Returns:

an empty Context

get

default <T> T get(Class<T> key)

Resolve a value given a type key within the Context.

Type Parameters:

T - an unchecked casted generic for fluent typing convenience

Parameters:

key - a type key to resolve the value within the context

Returns:

the value resolved for this type key (throws if key not found)

Throws:

NoSuchElementException - when the given type key is not present

See Also:

getOrDefault(Object, Object), getOrEmpty(Object)

get

<T> T get(Object key)

Resolve a value given a key that exists within the Context, or throw a NoSuchElementException if the key is not present.

Type Parameters:

T - an unchecked casted generic for fluent typing convenience

Parameters:

key - a lookup key to resolve the value within the context

Returns:

the value resolved for this key (throws if key not found)

Throws:

NoSuchElementException - when the given key is not present

See Also:

getOrDefault(Object, Object), getOrEmpty(Object), hasKey(Object)

getOrDefault

@Nullable
default <T> T getOrDefault(Object key,
                                     @Nullable
                                     T defaultValue)

Resolve a value given a key within the Context. If unresolved return the passed default value.

Parameters:

key - a lookup key to resolve the value within the context

defaultValue - a fallback value if key doesn't resolve

Returns:

the value resolved for this key, or the given default if not present

getOrEmpty

default <T> Optional<T> getOrEmpty(Object key)

Resolve a value given a key within the Context.

Parameters:

key - a lookup key to resolve the value within the context

Returns:

an Optional of the value for that key.

hasKey

boolean hasKey(Object key)

Return true if a particular key resolves to a value within the Context.

Parameters:

key - a lookup key to test for

Returns:

true if this context contains the given key

isEmpty

default boolean isEmpty()

Return true if the Context is empty.

Returns:

true if the Context is empty.

of

static Context of(Map<?,?> map)

Create a Context out of a Map. Prefer this method if you're somehow incapable of checking keys are all distinct in other of(Object, Object, Object, Object, Object, Object, Object, Object) implementations.

Implementation Note:

this method compacts smaller maps into a relevant fields-based implementation when map size is less than 6.

of

static Context of(Object key,
                  Object value)

Create a Context pre-initialized with one key-value pair.

Parameters:

key - the key to initialize.

value - the value for the key.

Returns:

a Context with a single entry.

Throws:

NullPointerException - if either key or value are null

of

static Context of(Object key1,
                  Object value1,
                  Object key2,
                  Object value2)

Create a Context pre-initialized with two key-value pairs.

Parameters:

key1 - the first key to initialize.

value1 - the value for the first key.

key2 - the second key to initialize.

value2 - the value for the second key.

Returns:

a Context with two entries.

Throws:

NullPointerException - if any key or value is null

of

static Context of(Object key1,
                  Object value1,
                  Object key2,
                  Object value2,
                  Object key3,
                  Object value3)

Create a Context pre-initialized with three key-value pairs.

Parameters:

key1 - the first key to initialize.

value1 - the value for the first key.

key2 - the second key to initialize.

value2 - the value for the second key.

key3 - the third key to initialize.

value3 - the value for the third key.

Returns:

a Context with three entries.

Throws:

NullPointerException - if any key or value is null

of

static Context of(Object key1,
                  Object value1,
                  Object key2,
                  Object value2,
                  Object key3,
                  Object value3,
                  Object key4,
                  Object value4)

Create a Context pre-initialized with four key-value pairs.

Parameters:

key1 - the first key to initialize.

value1 - the value for the first key.

key2 - the second key to initialize.

value2 - the value for the second key.

key3 - the third key to initialize.

value3 - the value for the third key.

key4 - the fourth key to initialize.

value4 - the value for the fourth key.

Returns:

a Context with four entries.

Throws:

NullPointerException - if any key or value is null

of

static Context of(Object key1,
                  Object value1,
                  Object key2,
                  Object value2,
                  Object key3,
                  Object value3,
                  Object key4,
                  Object value4,
                  Object key5,
                  Object value5)

Create a Context pre-initialized with five key-value pairs.

Parameters:

key1 - the first key to initialize.

value1 - the value for the first key.

key2 - the second key to initialize.

value2 - the value for the second key.

key3 - the third key to initialize.

value3 - the value for the third key.

key4 - the fourth key to initialize.

value4 - the value for the fourth key.

key5 - the fifth key to initialize.

value5 - the value for the fifth key.

Returns:

a Context with five entries.

Throws:

NullPointerException - if any key or value is null

put

Context put(Object key,
            Object value)

Create a new Context that contains all current key/value pairs plus the given key/value pair. If that key existed in the current Context, its associated value is replaced in the resulting Context.

Parameters:

key - the key to add/update in the new Context

value - the value to associate to the key in the new Context

Returns:

a new Context including the provided key/value

Throws:

NullPointerException - if either the key or value are null

putAll

default Context putAll(Context other)

Create a new Context by merging the content of this context and a given Context. If the other context is empty, the same Context instance is returned.

Parameters:

other - the other Context to get values from

Returns:

a new Context with a merge of the entries from this context and the given context.

putNonNull

default Context putNonNull(Object key,
                           @Nullable
                           Object valueOrNull)

Create a new Context that contains all current key/value pairs plus the given key/value pair only if the value is not null. If that key existed in the current Context, its associated value is replaced in the resulting Context.

Parameters:

key - the key to add/update in the new Context

valueOrNull - the value to associate to the key in the new Context, null to ignore the operation

Returns:

a new Context including the provided key/value, or the same Context if value is null

Throws:

NullPointerException - if the key is null

size

int size()

Return the size of this Context, the number of immutable key/value pairs stored inside it.

Returns:

the size of the Context

stream

Stream<Map.Entry<Object,Object>> stream()

Stream key/value pairs from this Context

Returns:

a Stream of key/value pairs held by this context