Java中的提供者 getService() 和 getServices() 方法

getService(字符串类型，字符串算法)

Java.security.Provider类的getService()方法用于获取描述该Provider对该算法或别名的指定类型的实现的服务。

如果不存在这样的实现，则此方法返回 null。如果有两个匹配的服务，一个使用 putService() 添加到此提供程序，一个通过 put() 添加，则返回通过 putService() 添加的服务。

句法：

public Provider.Service getService(String type, String algorithm)

参数：此方法将以下参数作为参数。

type – 请求的服务类型。
algorithm – 请求的服务的不区分大小写的算法名称（或备用别名）。

返回值：此方法返回描述此 Provider 的匹配服务的服务，如果不存在此类服务，则返回null 。

异常：如果类型或算法为空，此方法将抛出NullPointerException 。

以下是说明getService()方法的示例：

示例 1：

// Java program to demonstrate
// getService() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
  
        try {
            // creating the object of  SecureRandom
            Signature sr = Signature.getInstance("SHA1withDSA", "SUN");
  
            // getting the Provider of the SecureRandom sr
            // by using method getProvider()
            Provider provider = sr.getProvider();
  
            // getting the service of the provider using getServices() method
            Provider.Service service1 = provider
                                            .getService("Signature", sr.getAlgorithm());
  
            // printing the service
            System.out.println("Provider service : " + service1);
        }
  
        catch (NoSuchAlgorithmException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Provider service : SUN: Signature.SHA1withDSA -> sun.security.provider.DSA$SHA1withDSA
  aliases: [DSA, DSS, SHA/DSA, SHA-1/DSA, SHA1/DSA, SHAwithDSA, DSAWithSHA1, OID.1.2.840.10040.4.3, 1.2.840.10040.4.3, 1.3.14.3.2.13, 1.3.14.3.2.27]
  attributes: {ImplementedIn=Software, KeySize=1024, SupportedKeyClasses=java.security.interfaces.DSAPublicKey|java.security.interfaces.DSAPrivateKey}

示例 2：显示由 getService() 方法抛出的 NullPointerException。

// Java program to demonstrate
// getService() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
  
        try {
            // creating the object of  SecureRandom
            Signature sr = Signature.getInstance("SHA1withDSA", "SUN");
  
            // getting the Provider of the SecureRandom sr
            // by using method getProvider()
            Provider provider = sr.getProvider();
  
            // getting the service of the provider using getServices() method
            Provider.Service service1 = provider
                                            .getService(null, sr.getAlgorithm());
  
            // printing the service
            System.out.println("Provider service : " + service1);
        }
  
        catch (NoSuchAlgorithmException e) {
            System.out.println("Exception thrown : " + e);
        }
  
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Exception thrown : java.lang.NullPointerException

获取服务（）

Java.security.Provider类的getServices()方法用于获取此 Provider 支持的所有服务的不可修改 Set。

句法：

public Set getServices()

返回值：此方法返回此 Provider 支持的所有服务的不可修改的 Set 。

下面是说明 getServices() 方法的示例：

方案一：

// Java program to demonstrate
// getService() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
        // Declaring int variable
        int i = 5;
  
        try {
            // creating the object of  SecureRandom
            Signature sr = Signature.getInstance("SHA1withDSA", "SUN");
  
            // getting the Provider of the SecureRandom sr
            // by using method getProvider()
            Provider provider = sr.getProvider();
  
            // Declaring the variable of set type
            Set servicelist;
  
            // getting the service of the provider using getServices() method
            servicelist = provider.getServices();
  
            // Creating the object of iterator to iterate set
            Iterator iter = servicelist.iterator();
  
            // printing the set elements
            System.out.println("Provider servicelist : \n ");
            while (i > 0) {
                System.out.println("Value is : " + iter.next());
                i--;
            }
        }
  
        catch (NoSuchAlgorithmException e) {
            System.out.println("Exception thrown : " + e);
        }
  
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Provider servicelist : 
 
Value is : SUN: SecureRandom.NativePRNG -> sun.security.provider.NativePRNG

Value is : SUN: SecureRandom.SHA1PRNG -> sun.security.provider.SecureRandom
  attributes: {ImplementedIn=Software}

Value is : SUN: SecureRandom.NativePRNGBlocking -> sun.security.provider.NativePRNG$Blocking

Value is : SUN: SecureRandom.NativePRNGNonBlocking -> sun.security.provider.NativePRNG$NonBlocking

Value is : SUN: Signature.SHA1withDSA -> sun.security.provider.DSA$SHA1withDSA
  aliases: [DSA, DSS, SHA/DSA, SHA-1/DSA, SHA1/DSA, SHAwithDSA, DSAWithSHA1, OID.1.2.840.10040.4.3, 1.2.840.10040.4.3, 1.3.14.3.2.13, 1.3.14.3.2.27]
  attributes: {ImplementedIn=Software, KeySize=1024, SupportedKeyClasses=java.security.interfaces.DSAPublicKey|java.security.interfaces.DSAPrivateKey}