java.lang.Object
- io.grpc.Metadata

```
@NotThreadSafe
public final class Metadata
extends java.lang.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	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	Description
`static Metadata.AsciiMarshaller<java.lang.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 java.lang.String`	`BINARY_HEADER_SUFFIX`	All binary headers should have this suffix in their names.

Constructor Summary

Constructors
Constructor Description

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

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	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> java.lang.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.
`java.util.Set<java.lang.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, java.util.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> java.lang.Iterable<T>`	`removeAll(Metadata.Key<T> key)`	Remove all values for the given key.
`java.lang.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 java.lang.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<java.lang.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> java.lang.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 java.util.Set<java.lang.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:
    
    java.lang.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:
    
    java.lang.NullPointerException - if key or value is null
  - removeAll
```
public <T> java.lang.Iterable<T> removeAll(Metadata.Key<T> key)
```
    Remove all values for the given key. If there were no values, null is returned.
  - discardAll
```
@ExperimentalApi("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,
                  java.util.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 java.lang.String toString()
```
    Overrides:
    
    toString in class java.lang.Object

Class Metadata

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

BINARY_HEADER_SUFFIX

BINARY_BYTE_MARSHALLER

ASCII_STRING_MARSHALLER

Constructor Detail

Metadata

Method Detail

containsKey

get

getAll

keys

put

remove

removeAll

discardAll

merge

merge

toString