io.grpc

Class Metadata

java.lang.Object

io.grpc.Metadata

@NotThreadSafe
public final class Metadata
extends Object

Provides access to read and write metadata values to be exchanged during a call.

Keys are allowed to be associated with more than one value.

This class is not thread safe, implementations should ensure that header reads and writes do not occur in multiple threads concurrently.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	Metadata.AsciiMarshaller<T> Marshaller for metadata values that are serialized into ASCII strings.
static interface	Metadata.BinaryMarshaller<T> Marshaller for metadata values that are serialized into raw binary.
static interface	Metadata.BinaryStreamMarshaller<T> Marshaller for metadata values that are serialized to an InputStream.
static class	Metadata.Key<T> Key for metadata entries.

Field Summary

Fields

Modifier and Type	Field and Description
static Metadata.AsciiMarshaller<String>	ASCII_STRING_MARSHALLER Simple metadata marshaller that encodes strings as is.
static Metadata.BinaryMarshaller<byte[]>	BINARY_BYTE_MARSHALLER Simple metadata marshaller that encodes bytes as is.
static String	BINARY_HEADER_SUFFIX All binary headers should have this suffix in their names.

Constructor Summary

Constructors

Constructor and Description
Metadata() Constructor called by the application layer when it wants to send metadata.

Method Summary

Modifier and Type	Method and Description
boolean	containsKey(Metadata.Key<?> key) Returns true if a value is defined for the given key.
<T> void	discardAll(Metadata.Key<T> key) Remove all values for the given key without returning them.
<T> T	get(Metadata.Key<T> key) Returns the last metadata entry added with the name 'name' parsed as T.
<T> Iterable<T>	getAll(Metadata.Key<T> key) Returns all the metadata entries named 'name', in the order they were received, parsed as T, or null if there are none.
Set<String>	keys() Returns set of all keys in store.
void	merge(Metadata other) Perform a simple merge of two sets of metadata.
void	merge(Metadata other, Set<Metadata.Key<?>> keys) Merge values from the given set of keys into this set of metadata.
<T> void	put(Metadata.Key<T> key, T value) Adds the key, value pair.
<T> boolean	remove(Metadata.Key<T> key, T value) Removes the first occurrence of value for key.
<T> Iterable<T>	removeAll(Metadata.Key<T> key) Remove all values for the given key.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

BINARY_HEADER_SUFFIX

public static final String BINARY_HEADER_SUFFIX

All binary headers should have this suffix in their names. Vice versa.

Its value is "-bin". An ASCII header's name must not end with this.

See Also:

Constant Field Values

BINARY_BYTE_MARSHALLER

public static final Metadata.BinaryMarshaller<byte[]> BINARY_BYTE_MARSHALLER

Simple metadata marshaller that encodes bytes as is.

This should be used when raw bytes are favored over un-serialized version of object. Can be helpful in situations where more processing to bytes is needed on application side, avoids double encoding/decoding.

Both Metadata.BinaryMarshaller.toBytes(T) and Metadata.BinaryMarshaller.parseBytes(byte[]) methods do not return a copy of the byte array. Do _not_ modify the byte arrays of either the arguments or return values.

ASCII_STRING_MARSHALLER

public static final Metadata.AsciiMarshaller<String> ASCII_STRING_MARSHALLER

Simple metadata marshaller that encodes strings as is.

This should be used with ASCII strings that only contain the characters listed in the class comment of Metadata.AsciiMarshaller. Otherwise the output may be considered invalid and discarded by the transport, or the call may fail.

Constructor Detail

Metadata

public Metadata()

Constructor called by the application layer when it wants to send metadata.

Method Detail

containsKey

public boolean containsKey(Metadata.Key<?> key)

Returns true if a value is defined for the given key.

This is done by linear search, so if it is followed by get(io.grpc.Metadata.Key<T>) or getAll(io.grpc.Metadata.Key<T>), prefer calling them directly and checking the return value against null.

get

@Nullable
public <T> T get(Metadata.Key<T> key)

Returns the last metadata entry added with the name 'name' parsed as T.

Returns:

the parsed metadata entry or null if there are none.

getAll

@Nullable
public <T> Iterable<T> getAll(Metadata.Key<T> key)

Returns all the metadata entries named 'name', in the order they were received, parsed as T, or null if there are none. The iterator is not guaranteed to be "live." It may or may not be accurate if Metadata is mutated.

keys

public Set<String> keys()

Returns set of all keys in store.

Returns:

unmodifiable Set of keys

put

public <T> void put(Metadata.Key<T> key,
                    T value)

Adds the key, value pair. If key already has values, value is added to the end. Duplicate values for the same key are permitted.

Throws:

NullPointerException - if key or value is null

remove

public <T> boolean remove(Metadata.Key<T> key,
                          T value)

Removes the first occurrence of value for key.

Parameters:

key - key for value

value - value

Returns:

true if value removed; false if value was not present

Throws:

NullPointerException - if key or value is null

removeAll

public <T> Iterable<T> removeAll(Metadata.Key<T> key)

Remove all values for the given key. If there were no values, null is returned.

discardAll

@ExperimentalApi(value="https://github.com/grpc/grpc-java/issues/4691")
public <T> void discardAll(Metadata.Key<T> key)

Remove all values for the given key without returning them. This is a minor performance optimization if you do not need the previous values.

merge

public void merge(Metadata other)

Perform a simple merge of two sets of metadata.

This is a purely additive operation, because a single key can be associated with multiple values.

merge

public void merge(Metadata other,
                  Set<Metadata.Key<?>> keys)

Merge values from the given set of keys into this set of metadata. If a key is present in keys, then all of the associated values will be copied over.

Parameters:

other - The source of the new key values.

keys - The subset of matching key we want to copy, if they exist in the source.

toString

public String toString()

Overrides:

toString in class Object