Java中的 KeyPairGenerator getInstance() 方法及示例

getInstance(字符串算法)

Java.security.KeyPairGenerator类的getInstance()方法用于返回一个 KeyPairGenerator 对象，该对象为指定的算法生成公钥/私钥对。

此方法遍历已注册的安全提供者列表，从最喜欢的提供者开始。返回一个新的 KeyPairGenerator 对象，该对象封装来自支持指定算法的第一个 Provider 的 KeyPairGeneratorSpi 实现。

句法：

public static KeyPairGenerator 
    getInstance(String algorithm)
        throws NoSuchAlgorithmException

参数：该方法以算法的标准名称为参数。

返回值：此方法返回新的 KeyPairGenerator 对象。

异常：如果没有提供者支持指定算法的签名实现，则此方法抛出NoSuchAlgorithmException 。

下面是说明getInstance()方法的示例：

示例 1：

// Java program to demonstrate
// getInstance() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
            // creating the object of
            // KeyPairGenerator
            // and getting instance
            // using getInstance() method
            KeyPairGenerator sr = KeyPairGenerator.getInstance("DSA");
  
            // getting the Algorithm
            String algo = sr.getAlgorithm();
  
            // printing the algo String
            System.out.println("Algorithm : " + algo);
        }
  
        catch (NoSuchAlgorithmException e) {
  
            System.out.println("Exception thrown : " + e);
        }
        catch (ProviderException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Algorithm : DSA

示例 2：显示 NoSuchAlgorithmException

// Java program to demonstrate
// getInstance() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
            // creating the object of
            // KeyPairGenerator
            // and getting instance
            // using getInstance() method
  
            System.out.println("Trying to get"
                               + " the instance of unknown Algorithm");
  
            KeyPairGenerator sr = KeyPairGenerator
                                      .getInstance("TAJMAHAL");
  
            // getting the Algorithm
            String algo = sr.getAlgorithm();
  
            // printing the algo String
            System.out.println("Algorithm : " + algo);
        }
  
        catch (NoSuchAlgorithmException e) {
  
            System.out.println("Exception thrown : " + e);
        }
        catch (ProviderException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Trying to get the instance of unknown Algorithm
Exception thrown : java.security.NoSuchAlgorithmException: TAJMAHAL KeyPairGenerator not available

getInstance(字符串算法，Provider提供者)

Java.security.KeyPairGenerator 类的getInstance()方法用于返回一个 KeyPairGenerator 对象，该对象为指定的算法生成公钥/私钥对。
返回一个新的 KeyPairGenerator 对象，该对象封装了来自指定 Provider 对象的 KeyPairGeneratorSpi 实现。请注意，指定的提供者对象不必在提供者列表中注册。

句法：

public static KeyPairGenerator 
    getInstance(String algorithm, Provider provider)
        throws NoSuchAlgorithmException

参数：此方法将以下参数作为参数：

• algorithm ：请求的算法的名称。
• 提供者：提供者

返回值：此方法返回新的 KeyPairGenerator 对象。

异常：此方法抛出以下异常：

• NoSuchAlgorithmException – 如果指定算法的 SignatureSpi 实现不能从指定的 Provider 对象获得。
• IllegalArgumentException–如果提供者为空。

  下面是说明getInstance()方法的示例：

  注意：以下程序不会在在线 IDE 上运行。

  示例 1：

  // Java program to demonstrate
  // getInstance() method
    
  import java.security.*;
  import java.util.*;
    
  public class GFG1 {
      public static void main(String[] argv)
      {
          try {
              // creating the object of
              // KeyPairGenerator
              // and getting instance
              // using getInstance() method
              KeyPairGenerator sr = KeyPairGenerator.getInstance("DSA");
    
              // creating Provider object
              Provider pd = sr.getProvider();
    
              // getting algorithm name
              // by using getAlgorithm() mathod
              String algo = sr.getAlgorithm();
    
              // creating the object of KeyPairGenerator and getting instance
              // By usng getInstance() method
              KeyPairGenerator sr1 = KeyPairGenerator.getInstance(algo, pd);
    
              // getting the status of signature object
              KeyPair keypair = sr1.generateKeyPair();
    
              // printing the keypair
              System.out.println("Keypair : " + keypair);
          }
    
          catch (NoSuchAlgorithmException e) {
    
              System.out.println("Exception thrown : " + e);
          }
          catch (ProviderException e) {
    
              System.out.println("Exception thrown : " + e);
          }
      }
  }
  

  输出：

  Keypair : java.security.KeyPair@12a3a380
  

  示例 2：显示 NoSuchAlgorithmException

  // Java program to demonstrate
  // getInstance() method
    
  import java.security.*;
  import java.util.*;
    
  public class GFG1 {
      public static void main(String[] argv)
      {
          try {
              // creating the object of
              // KeyPairGenerator
              // and getting instance
              // using getInstance() method
              KeyPairGenerator sr = KeyPairGenerator.getInstance("DSA");
    
              // creating Provider object
              Provider pd = sr.getProvider();
    
              // creating the object of KeyPairGenerator and getting instance
              // By usng getInstance() method
              KeyPairGenerator sr1 = KeyPairGenerator.getInstance("TAJMAHAL", pd);
    
              // getting the status of signature object
              KeyPair keypair = sr1.generateKeyPair();
    
              // printing the keypair
              System.out.println("Keypair : " + keypair);
          }
    
          catch (NoSuchAlgorithmException e) {
    
              System.out.println("Exception thrown : " + e);
          }
          catch (ProviderException e) {
    
              System.out.println("Exception thrown : " + e);
          }
      }
  }
  

  输出：

  Exception thrown : java.security.NoSuchAlgorithmException: 
  no such algorithm: TAJMAHAL for provider SUN
  

  示例 3：显示 IllegalArgumentException

  // Java program to demonstrate
  // getInstance() method
    
  import java.security.*;
  import java.util.*;
    
  public class GFG1 {
      public static void main(String[] argv)
      {
          try {
              // creating the object of
              // KeyPairGenerator
              // and getting instance
              // using getInstance() method
              KeyPairGenerator sr = KeyPairGenerator
                                        .getInstance("RSA");
    
              // creating Provider object
              System.out.println("Trying to assign null as a provider");
              Provider pd = null;
    
              // getting algorithm name
              // by using     getAlgorithm() mathod
              String algo = sr.getAlgorithm();
    
              // creating the object of KeyPairGenerator and getting instance
              // By usng getInstance() method
              KeyPairGenerator sr1 = KeyPairGenerator
                                         .getInstance(algo, pd);
    
              // getting the status of signature object
              KeyPair keypair = sr1.generateKeyPair();
    
              // printing the keypair
              System.out.println("Keypair : " + keypair);
          }
    
          catch (NoSuchAlgorithmException e) {
    
              System.out.println("Exception thrown : " + e);
          }
          catch (ProviderException e) {
    
              System.out.println("Exception thrown : " + e);
          }
          catch (IllegalArgumentException e) {
    
              System.out.println("Exception thrown : " + e);
          }
      }
  }
  

  输出：

  Trying to assign null as a provider
  Exception thrown : java.lang.IllegalArgumentException:
   missing provider