Module java.base
Package javax.net.ssl

# Class SSLParameters

java.lang.Object
javax.net.ssl.SSLParameters

public class SSLParameters extends Object
Encapsulates parameters for an SSL/TLS/DTLS connection. The parameters are the list of ciphersuites to be accepted in an SSL/TLS/DTLS handshake, the list of protocols to be allowed, the endpoint identification algorithm during SSL/TLS/DTLS handshaking, the Server Name Indication (SNI), the maximum network packet size, the algorithm constraints, the signature schemes, the key exchange named groups and whether SSL/TLS/DTLS servers should request or require client authentication, etc.

`SSLParameter` objects can be created via the constructors in this class, and can be described as pre-populated objects. `SSLParameter` objects can also be obtained using the `getSSLParameters()` methods in `SSLSocket` and `SSLServerSocket` and `SSLEngine` or the `getDefaultSSLParameters()` and `getSupportedSSLParameters()` methods in `SSLContext`, and can be described as connection populated objects.

SSLParameters can be applied to a connection via the methods `SSLSocket.setSSLParameters()` and `SSLServerSocket.setSSLParameters()` and `SSLEngine.setSSLParameters()`.

For example:

>          SSLParameters p = sslSocket.getSSLParameters();
>          p.setProtocols(new String[] { "TLSv1.2" });
>          p.setCipherSuites(
>              new String[] { "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256", ... });
>          p.setApplicationProtocols(new String[] {"h2", "http/1.1"});
>          sslSocket.setSSLParameters(p);

Since:
  1.6
See Also:
  - `SSLSocket`
  - `SSLEngine`
  - `SSLContext`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `SSLParameters()`
  Constructs SSLParameters.
  `SSLParameters(String[] cipherSuites)`
  Constructs SSLParameters from the specified array of ciphersuites.
  `SSLParameters(String[] cipherSuites, String[] protocols)`
  Constructs SSLParameters from the specified array of ciphersuites and protocols.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `AlgorithmConstraints`
  `getAlgorithmConstraints()`
  Returns the cryptographic algorithm constraints.
  `String[]`
  `getApplicationProtocols()`
  Returns a prioritized array of application-layer protocol names that can be negotiated over the SSL/TLS/DTLS protocols.
  `String[]`
  `getCipherSuites()`
  Returns a copy of the array of ciphersuites or null if none have been set.
  `boolean`
  `getEnableRetransmissions()`
  Returns whether DTLS handshake retransmissions should be enabled.
  `String`
  `getEndpointIdentificationAlgorithm()`
  Gets the endpoint identification algorithm.
  `int`
  `getMaximumPacketSize()`
  Returns the maximum expected network packet size in bytes for SSL/TLS/DTLS records.
  `String[]`
  `getNamedGroups()`
  Returns a prioritized array of key exchange named groups names that can be used over the SSL/TLS/DTLS protocols.
  `boolean`
  `getNeedClientAuth()`
  Returns whether client authentication should be required.
  `String[]`
  `getProtocols()`
  Returns a copy of the array of protocols or null if none have been set.
  `final List<SNIServerName>`
  `getServerNames()`
  Returns a `List` containing all `SNIServerName`s of the Server Name Indication (SNI) parameter, or null if none has been set.
  `String[]`
  `getSignatureSchemes()`
  Returns a prioritized array of signature scheme names that can be used over the SSL/TLS/DTLS protocols.
  `final Collection<SNIMatcher>`
  `getSNIMatchers()`
  Returns a `Collection` containing all `SNIMatcher`s of the Server Name Indication (SNI) parameter, or null if none has been set.
  `final boolean`
  `getUseCipherSuitesOrder()`
  Returns whether the local cipher suites preference should be honored.
  `boolean`
  `getWantClientAuth()`
  Returns whether client authentication should be requested.
  `void`
  `setAlgorithmConstraints(AlgorithmConstraints constraints)`
  Sets the cryptographic algorithm constraints, which will be used in addition to any configured by the runtime environment.
  `void`
  `setApplicationProtocols(String[] protocols)`
  Sets the prioritized array of application-layer protocol names that can be negotiated over the SSL/TLS/DTLS protocols.
  `void`
  `setCipherSuites(String[] cipherSuites)`
  Sets the array of ciphersuites.
  `void`
  `setEnableRetransmissions(boolean enableRetransmissions)`
  Sets whether DTLS handshake retransmissions should be enabled.
  `void`
  `setEndpointIdentificationAlgorithm(String algorithm)`
  Sets the endpoint identification algorithm.
  `void`
  `setMaximumPacketSize(int maximumPacketSize)`
  Sets the maximum expected network packet size in bytes for SSL/TLS/DTLS records.
  `void`
  `setNamedGroups(String[] namedGroups)`
  Sets the prioritized array of key exchange named groups names that can be used over the SSL/TLS/DTLS protocols.
  `void`
  `setNeedClientAuth(boolean needClientAuth)`
  Sets whether client authentication should be required.
  `void`
  `setProtocols(String[] protocols)`
  Sets the array of protocols.
  `final void`
  `setServerNames(List<SNIServerName> serverNames)`
  Sets the desired `SNIServerName`s of the Server Name Indication (SNI) parameter.
  `void`
  `setSignatureSchemes(String[] signatureSchemes)`
  Sets the prioritized array of signature scheme names that can be used over the SSL/TLS/DTLS protocols.
  `final void`
  `setSNIMatchers(Collection<SNIMatcher> matchers)`
  Sets the `SNIMatcher`s of the Server Name Indication (SNI) parameter.
  `final void`
  `setUseCipherSuitesOrder(boolean honorOrder)`
  Sets whether the local cipher suites preference should be honored.
  `void`
  `setWantClientAuth(boolean wantClientAuth)`
  Sets whether client authentication should be requested.

  ### Methods declared in class java.lang.Object

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

- ## Constructor Details

  - ### SSLParameters

    public SSLParameters()
    Constructs SSLParameters.

    The values of cipherSuites, protocols, cryptographic algorithm constraints, endpoint identification algorithm, signature schemes, server names and server name matchers are set to `null`; useCipherSuitesOrder, wantClientAuth and needClientAuth are set to `false`; enableRetransmissions is set to `true`; maximum network packet size is set to `0`.

  - ### SSLParameters

    public SSLParameters(String[] cipherSuites)
    Constructs SSLParameters from the specified array of ciphersuites.

    Calling this constructor is equivalent to calling the no-args constructor followed by `setCipherSuites(cipherSuites);`. Note that the standard list of cipher suite names may be found in the JSSE Cipher Suite Names section of the Java Security Standard Algorithm Names Specification. Providers may support cipher suite names not found in this list.

    Parameters:
      `cipherSuites` - the array of ciphersuites (or null)

  - ### SSLParameters

    public SSLParameters(String[] cipherSuites, String[] protocols)
    Constructs SSLParameters from the specified array of ciphersuites and protocols.

    Calling this constructor is equivalent to calling the no-args constructor followed by `setCipherSuites(cipherSuites); setProtocols(protocols);`. Note that the standard list of cipher suite names may be found in the JSSE Cipher Suite Names section of the Java Security Standard Algorithm Names Specification. Providers may support cipher suite names not found in this list.

    Parameters:
      `cipherSuites` - the array of ciphersuites (or null)
      `protocols` - the array of protocols (or null)

- ## Method Details

  - ### getCipherSuites

    public String[] getCipherSuites()
    Returns a copy of the array of ciphersuites or null if none have been set.

    The returned array includes cipher suites from the list of standard cipher suite names in the JSSE Cipher Suite Names section of the Java Security Standard Algorithm Names Specification, and may also include other cipher suites that the provider supports.

    Returns:
      a copy of the array of ciphersuites or null if none have been set.

  - ### setCipherSuites

    public void setCipherSuites(String[] cipherSuites)
    Sets the array of ciphersuites.
    Parameters:
      `cipherSuites` - the array of ciphersuites (or null). Note that the standard list of cipher suite names may be found in the JSSE Cipher Suite Names section of the Java Security Standard Algorithm Names Specification. Providers may support cipher suite names not found in this list or might not use the recommended name for a certain cipher suite.

  - ### getProtocols

    public String[] getProtocols()
    Returns a copy of the array of protocols or null if none have been set.
    Returns:
      a copy of the array of protocols or null if none have been set.

  - ### setProtocols

    public void setProtocols(String[] protocols)
    Sets the array of protocols.
    Parameters:
      `protocols` - the array of protocols (or null)

  - ### getWantClientAuth

    public boolean getWantClientAuth()
    Returns whether client authentication should be requested.
    Returns:
      whether client authentication should be requested.

  - ### setWantClientAuth

    public void setWantClientAuth(boolean wantClientAuth)
    Sets whether client authentication should be requested. Calling this method clears the `needClientAuth` flag.
    Parameters:
      `wantClientAuth` - whether client authentication should be requested

  - ### getNeedClientAuth

    public boolean getNeedClientAuth()
    Returns whether client authentication should be required.
    Returns:
      whether client authentication should be required.

  - ### setNeedClientAuth

    public void setNeedClientAuth(boolean needClientAuth)
    Sets whether client authentication should be required. Calling this method clears the `wantClientAuth` flag.
    Parameters:
      `needClientAuth` - whether client authentication should be required

  - ### getAlgorithmConstraints

    public AlgorithmConstraints getAlgorithmConstraints()
    Returns the cryptographic algorithm constraints.
    Returns:
      the cryptographic algorithm constraints, or null if the constraints have not been set
    Since:
      1.7
    See Also:
      - `setAlgorithmConstraints(AlgorithmConstraints)`

  - ### setAlgorithmConstraints

    public void setAlgorithmConstraints(AlgorithmConstraints constraints)
    Sets the cryptographic algorithm constraints, which will be used in addition to any configured by the runtime environment.

    If the `constraints` parameter is non-null, every cryptographic algorithm, key and algorithm parameters used in the SSL/TLS/DTLS handshake must be permitted by the constraints.

    Parameters:
      `constraints` - the algorithm constraints (or null)
    Since:
      1.7

  - ### getEndpointIdentificationAlgorithm

    public String getEndpointIdentificationAlgorithm()
    Gets the endpoint identification algorithm.
    Returns:
      the endpoint identification algorithm, or null if none has been set.
    Since:
      1.7
    See Also:
      - `X509ExtendedTrustManager`
      - `setEndpointIdentificationAlgorithm(String)`

  - ### setEndpointIdentificationAlgorithm

    public void setEndpointIdentificationAlgorithm(String algorithm)
    Sets the endpoint identification algorithm.

    If the `algorithm` parameter is non-null or non-empty, the endpoint identification/verification procedures must be handled during SSL/TLS/DTLS handshaking. This is to prevent man-in-the-middle attacks.

    Parameters:
      `algorithm` - The standard string name of the endpoint identification algorithm (or null). See the Java Security Standard Algorithm Names document for information about standard algorithm names.
    Since:
      1.7
    See Also:
      - `X509ExtendedTrustManager`

  - ### setServerNames

    public final void setServerNames(List<SNIServerName> serverNames)
    Sets the desired `SNIServerName`s of the Server Name Indication (SNI) parameter.

    This method is only useful to `SSLSocket`s or `SSLEngine`s operating in client mode.

    Note that the `serverNames` list is cloned to protect against subsequent modification.

    Parameters:
      `serverNames` - the list of desired `SNIServerName`s (or null)
    Throws:
      `NullPointerException` - if the `serverNames` contains `null` element
      `IllegalArgumentException` - if the `serverNames` contains more than one name of the same name type
    Since:
      1.8
    See Also:
      - `SNIServerName`
      - `getServerNames()`

  - ### getServerNames

    public final List<SNIServerName> getServerNames()
    Returns a `List` containing all `SNIServerName`s of the Server Name Indication (SNI) parameter, or null if none has been set.

    This method is only useful to `SSLSocket`s or `SSLEngine`s operating in client mode.

    For SSL/TLS/DTLS connections, the underlying SSL/TLS/DTLS provider may specify a default value for a certain server name type. In client mode, it is recommended that, by default, providers should include the server name indication whenever the server can be located by a supported server name type.

    It is recommended that providers initialize default Server Name Indications when creating `SSLSocket`/`SSLEngine`s. In the following examples, the server name may be represented by an instance of `SNIHostName` which has been initialized with the hostname "www.example.com" and type `StandardConstants.SNI_HOST_NAME`.

             Socket socket =
                 sslSocketFactory.createSocket("www.example.com", 443);

    or

             SSLEngine engine =
                 sslContext.createSSLEngine("www.example.com", 443);

    Returns:
      null or an immutable list of non-null `SNIServerName`s
    Since:
      1.8
    See Also:
      - `List`
      - `setServerNames(List)`

  - ### setSNIMatchers

    public final void setSNIMatchers(Collection<SNIMatcher> matchers)
    Sets the `SNIMatcher`s of the Server Name Indication (SNI) parameter.

    This method is only useful to `SSLSocket`s or `SSLEngine`s operating in server mode.

    Note that the `matchers` collection is cloned to protect against subsequent modification.

    Parameters:
      `matchers` - the collection of `SNIMatcher`s (or null)
    Throws:
      `NullPointerException` - if the `matchers` contains `null` element
      `IllegalArgumentException` - if the `matchers` contains more than one name of the same name type
    Since:
      1.8
    See Also:
      - `Collection`
      - `SNIMatcher`
      - `getSNIMatchers()`

  - ### getSNIMatchers

    public final Collection<SNIMatcher> getSNIMatchers()
    Returns a `Collection` containing all `SNIMatcher`s of the Server Name Indication (SNI) parameter, or null if none has been set.

    This method is only useful to `SSLSocket`s or `SSLEngine`s operating in server mode.

    For better interoperability, providers generally will not define default matchers so that by default servers will ignore the SNI extension and continue the handshake.

    Returns:
      null or an immutable collection of non-null `SNIMatcher`s
    Since:
      1.8
    See Also:
      - `SNIMatcher`
      - `setSNIMatchers(Collection)`

  - ### setUseCipherSuitesOrder

    public final void setUseCipherSuitesOrder(boolean honorOrder)
    Sets whether the local cipher suites preference should be honored.
    Parameters:
      `honorOrder` - whether local cipher suites order in `#getCipherSuites` should be honored during SSL/TLS/DTLS handshaking.
    Since:
      1.8
    See Also:
      - `getUseCipherSuitesOrder()`

  - ### getUseCipherSuitesOrder

    public final boolean getUseCipherSuitesOrder()
    Returns whether the local cipher suites preference should be honored.
    Returns:
      whether local cipher suites order in `#getCipherSuites` should be honored during SSL/TLS/DTLS handshaking.
    Since:
      1.8
    See Also:
      - `setUseCipherSuitesOrder(boolean)`

  - ### setEnableRetransmissions

    public void setEnableRetransmissions(boolean enableRetransmissions)
    Sets whether DTLS handshake retransmissions should be enabled. This method only applies to DTLS.
    Parameters:
      `enableRetransmissions` - `true` indicates that DTLS handshake retransmissions should be enabled; `false` indicates that DTLS handshake retransmissions should be disabled
    Since:
      9
    See Also:
      - `getEnableRetransmissions()`

  - ### getEnableRetransmissions

    public boolean getEnableRetransmissions()
    Returns whether DTLS handshake retransmissions should be enabled. This method only applies to DTLS.
    Returns:
      true, if DTLS handshake retransmissions should be enabled
    Since:
      9
    See Also:
      - `setEnableRetransmissions(boolean)`

  - ### setMaximumPacketSize

    public void setMaximumPacketSize(int maximumPacketSize)
    Sets the maximum expected network packet size in bytes for SSL/TLS/DTLS records.
    API Note:
      It is recommended that if possible, the maximum packet size should not be less than 256 bytes so that small handshake messages, such as HelloVerifyRequests, are not fragmented.
    Implementation Note:
      If the maximum packet size is too small to hold a minimal record, an implementation may attempt to generate as minimal records as possible. However, this may cause a generated packet to be larger than the maximum packet size.
    Parameters:
      `maximumPacketSize` - the maximum expected network packet size in bytes, or `0` to use the implicit size that is automatically specified by the underlying implementation.
    Throws:
      `IllegalArgumentException` - if `maximumPacketSize` is negative.
    Since:
      9
    See Also:
      - `getMaximumPacketSize()`

  - ### getMaximumPacketSize

    public int getMaximumPacketSize()
    Returns the maximum expected network packet size in bytes for SSL/TLS/DTLS records.
    API Note:
      The implicit size may not be a fixed value, especially for a DTLS protocols implementation.
    Implementation Note:
      For SSL/TLS/DTLS connections, the underlying provider should calculate and specify the implicit value of the maximum expected network packet size if it is not configured explicitly. For any connection populated object, this method should never return `0` so that applications can retrieve the actual implicit size of the underlying implementation.

      An implementation should attempt to comply with the maximum packet size configuration. However, if the maximum packet size is too small to hold a minimal record, an implementation may try to generate as minimal records as possible. This may cause a generated packet to be larger than the maximum packet size.

    Returns:
      the maximum expected network packet size, or `0` if use the implicit size that is automatically specified by the underlying implementation and this object has not been populated by any connection.
    Since:
      9
    See Also:
      - `setMaximumPacketSize(int)`

  - ### getApplicationProtocols

    public String[] getApplicationProtocols()
    Returns a prioritized array of application-layer protocol names that can be negotiated over the SSL/TLS/DTLS protocols.

    The array could be empty (zero-length), in which case protocol indications will not be used.

    This method will return a new array each time it is invoked.

    Returns:
      a non-null, possibly zero-length array of application protocol `String`s. The array is ordered based on protocol preference, with the first entry being the most preferred.
    Since:
      9
    See Also:
      - `setApplicationProtocols(java.lang.String[])`

  - ### setApplicationProtocols

    public void setApplicationProtocols(String[] protocols)
    Sets the prioritized array of application-layer protocol names that can be negotiated over the SSL/TLS/DTLS protocols.

    If application-layer protocols are supported by the underlying SSL/TLS implementation, this method configures which values can be negotiated by protocols such as RFC 7301 , the Application Layer Protocol Negotiation (ALPN).

    If this end of the connection is expected to offer application protocol values, all protocols configured by this method will be sent to the peer.

    If this end of the connection is expected to select the application protocol value, the `protocols` configured by this method are compared with those sent by the peer. The first matched value becomes the negotiated value. If none of the `protocols` were actually requested by the peer, the underlying protocol will determine what action to take. (For example, ALPN will send a `"no_application_protocol"` alert and terminate the connection.)

    The `String` values must be presented using the network byte representation expected by the peer. For example, if an ALPN `String` should be exchanged using `UTF-8`, the `String` should be converted to its `byte[]` representation and stored as a byte-oriented `String` before calling this method.

    >          // MEETEI MAYEK LETTERS HUK UN I (Unicode 0xabcd->0xabcf): 2 bytes
    >          byte[] bytes = "\uabcd\uabce\uabcf"
    >                  .getBytes(StandardCharsets.UTF_8);
    >          String HUK_UN_I = new String(bytes, StandardCharsets.ISO_8859_1);

    >          // 0x00-0xFF:  1 byte
    >          String rfc7301Grease8A = "\u008A\u008A";

    >          SSLParameters p = sslSocket.getSSLParameters();
    >          p.setApplicationProtocols(new String[] {
    >                  "h2", "http/1.1", rfc7301Grease8A, HUK_UN_I});
    >          sslSocket.setSSLParameters(p);

    Implementation Requirements:
      This method will make a copy of the `protocols` array.
    Parameters:
      `protocols` - an ordered array of application protocols, with `protocols[0]` being the most preferred. If the array is empty (zero-length), protocol indications will not be used.
    Throws:
      `IllegalArgumentException` - if protocols is null, or if any element in a non-empty array is null or an empty (zero-length) string
    Since:
      9
    See Also:
      - `getApplicationProtocols()`

  - ### getSignatureSchemes

    public String[] getSignatureSchemes()
    Returns a prioritized array of signature scheme names that can be used over the SSL/TLS/DTLS protocols.

    Note that the standard list of signature scheme names are defined in the Signature Schemes section of the Java Security Standard Algorithm Names Specification. Providers may support signature schemes not defined in this list or may not use the recommended name for a certain signature scheme.

    The set of signature schemes that will be used over the SSL/TLS/DTLS connections is determined by the returned array of this method and the underlying provider-specific default signature schemes.

    If the returned array is `null`, then the underlying provider-specific default signature schemes will be used over the SSL/TLS/DTLS connections.

    If the returned array is empty (zero-length), then the signature scheme negotiation mechanism is turned off for SSL/TLS/DTLS protocols, and the connections may not be able to be established if the negotiation mechanism is required by a certain SSL/TLS/DTLS protocol. This parameter will override the underlying provider-specific default signature schemes.

    If the returned array is not `null` or empty (zero-length), then the signature schemes in the returned array will be used over the SSL/TLS/DTLS connections. This parameter will override the underlying provider-specific default signature schemes.

    This method returns the most recent value passed to `setSignatureSchemes(java.lang.String[])` if that method has been called and otherwise returns the default signature schemes for connection populated objects, or `null` for pre-populated objects.

    API Note:
      Note that a provider may not have been updated to support this method and in that case may return `null` instead of the default signature schemes for connection populated objects.
    Implementation Note:
      The SunJSSE provider supports this method., Note that applications may use the `jdk.tls.client.SignatureSchemes` and/or `jdk.tls.server.SignatureSchemes` system properties with the SunJSSE provider to override the provider-specific default signature schemes.
    Returns:
      an array of signature scheme `Strings` or `null` if none have been set. For non-null returns, this method will return a new array each time it is invoked. The array is ordered based on signature scheme preference, with the first entry being the most preferred. Providers should ignore unknown signature scheme names while establishing the SSL/TLS/DTLS connections.
    Since:
      19
    See Also:
      - `setSignatureSchemes(java.lang.String[])`

  - ### setSignatureSchemes

    public void setSignatureSchemes(String[] signatureSchemes)
    Sets the prioritized array of signature scheme names that can be used over the SSL/TLS/DTLS protocols.

    Note that the standard list of signature scheme names are defined in the Signature Schemes section of the Java Security Standard Algorithm Names Specification. Providers may support signature schemes not defined in this list or may not use the recommended name for a certain signature scheme.

    The set of signature schemes that will be used over the SSL/TLS/DTLS connections is determined by the input parameter `signatureSchemes` array and the underlying provider-specific default signature schemes. See `getSignatureSchemes()` for specific details on how the parameters are used in SSL/TLS/DTLS connections.

    API Note:
      Note that a provider may not have been updated to support this method and in that case may ignore the schemes that are set.
    Implementation Note:
      The SunJSSE provider supports this method.
    Parameters:
      `signatureSchemes` - an ordered array of signature scheme names with the first entry being the most preferred, or `null`. This method will make a copy of this array. Providers should ignore unknown signature scheme names while establishing the SSL/TLS/DTLS connections.
    Throws:
      `IllegalArgumentException` - if any element in the `signatureSchemes` array is `null` or blank.
    Since:
      19
    See Also:
      - `getSignatureSchemes()`

  - ### getNamedGroups

    public String[] getNamedGroups()
    Returns a prioritized array of key exchange named groups names that can be used over the SSL/TLS/DTLS protocols.

    Note that the standard list of key exchange named groups are defined in the Named Groups section of the Java Security Standard Algorithm Names Specification. Providers may support named groups not defined in this list or may not use the recommended name for a certain named group.

    The set of named groups that will be used over the SSL/TLS/DTLS connections is determined by the returned array of this method and the underlying provider-specific default named groups.

    If the returned array is `null`, then the underlying provider-specific default named groups will be used over the SSL/TLS/DTLS connections.

    If the returned array is empty (zero-length), then the named group negotiation mechanism is turned off for SSL/TLS/DTLS protocols, and the connections may not be able to be established if the negotiation mechanism is required by a certain SSL/TLS/DTLS protocol. This parameter will override the underlying provider-specific default name groups.

    If the returned array is not `null` or empty (zero-length), then the named groups in the returned array will be used over the SSL/TLS/DTLS connections. This parameter will override the underlying provider-specific default named groups.

    This method returns the most recent value passed to `setNamedGroups(java.lang.String[])` if that method has been called and otherwise returns the default named groups for connection populated objects, or `null` for pre-populated objects.

    API Note:
      Note that a provider may not have been updated to support this method and in that case may return `null` instead of the default named groups for connection populated objects.
    Implementation Note:
      The SunJSSE provider supports this method., Note that applications may use the `jdk.tls.namedGroups` system property with the SunJSSE provider to override the provider-specific default named groups.
    Returns:
      an array of key exchange named group names `Strings` or `null` if none have been set. For non-null returns, this method will return a new array each time it is invoked. The array is ordered based on named group preference, with the first entry being the most preferred. Providers should ignore unknown named group names while establishing the SSL/TLS/DTLS connections.
    Since:
      20
    See Also:
      - `setNamedGroups(java.lang.String[])`

  - ### setNamedGroups

    public void setNamedGroups(String[] namedGroups)
    Sets the prioritized array of key exchange named groups names that can be used over the SSL/TLS/DTLS protocols.

    Note that the standard list of key exchange named groups are defined in the Named Groups section of the Java Security Standard Algorithm Names Specification. Providers may support named groups not defined in this list or may not use the recommended name for a certain named group.

    The set of named groups that will be used over the SSL/TLS/DTLS connections is determined by the input parameter `namedGroups` array and the underlying provider-specific default named groups. See `getNamedGroups()` for specific details on how the parameters are used in SSL/TLS/DTLS connections.

    API Note:
      Note that a provider may not have been updated to support this method and in that case may ignore the named groups that are set.
    Implementation Note:
      The SunJSSE provider supports this method.
    Parameters:
      `namedGroups` - an ordered array of key exchange named group names with the first entry being the most preferred, or `null`. This method will make a copy of this array. Providers should ignore unknown named group scheme names while establishing the SSL/TLS/DTLS connections.
    Throws:
      `IllegalArgumentException` - if any element in the `namedGroups` array is a duplicate, `null` or blank.
    Since:
      20
    See Also:
      - `getNamedGroups()`