Java中的 KeyFactory getInstance() 方法及示例

getInstance(字符串算法)

Java.security.KeyFactory类的getInstance()方法返回一个 KeyFactory 类型的对象，该对象应用分配的 KeyFactory 算法。

句法：

public static KeyFactory
  getInstance(String algorithm)
  throws NoSuchAlgorithmException

参数：此方法寻求标准算法作为参数，其实例将被创建到此 KeyFactory 实例。

返回值：此方法返回一个新的密钥工厂对象。

异常：此方法抛出以下异常：

• NoSuchAlgorithmException：如果没有提供程序可用于支持特定算法的密钥工厂 spi 应用程序。
• NullPointerException：如果算法为空。

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 KeyFactory
            // and getting instance
            // By using getInstance() method
            KeyFactory sr
                = KeyFactory.getInstance("DSA");
  
            // getting the algorithm of KeyFactory object
            String str = sr.getAlgorithm();
  
            // printing the status
            System.out.println("algorithm : " + str);
        }
  
        catch (NoSuchAlgorithmException e) {
  
            System.out.println("Exception thrown : " + e);
        }
        catch (NullPointerException 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 KeyFactory
            // and getting instance
            // By using getInstance() method
            KeyFactory sr = KeyFactory.getInstance("GEEKS");
  
            // getting the algorithm of KeyFactory object
            String str = sr.getAlgorithm();
  
            // printing the status
            System.out.println("algorithm : " + str);
        }
  
        catch (NoSuchAlgorithmException e) {
  
            System.out.println("Exception thrown : " + e);
        }
        catch (NullPointerException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Exception thrown :
 java.security.NoSuchAlgorithmException:
 GEEKS KeyFactory not available

getInstance（字符串算法，字符串提供者）

Java.security.KeyFactory类的getInstance()方法返回一个 KeyFactory 类型的对象，该对象应用分配的 KeyFactory 算法和分配的提供者对象。

句法：

public static KeyFactory
  getInstance(String algorithm, String provider)
  throws NoSuchAlgorithmException

参数：此方法寻求以下参数作为参数：

• algorithm ：这是指定用于获取实例的算法的名称。
• provider ：这是要指定的提供者的名称

返回值：此方法返回一个新的密钥工厂对象。

异常：此方法抛出以下异常：

• NoSuchAlgorithmException: – 如果没有提供程序可用于支持特定算法的密钥工厂 spi 应用程序。
• IllegalArgumentException: – 如果提供者为空。
• NullPointerException: – 如果算法为空

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 KeyFactory
            // and getting instance
            // By using getInstance() method
            KeyFactory sr
                = KeyFactory.getInstance(
                    "DSA", "SUN");
  
            // getting the algorithm of KeyFactory object
            String str = sr.getAlgorithm();
  
            // printing the status
            System.out.println("algorithm : " + str);
        }
  
        catch (NoSuchAlgorithmException e) {
  
            System.out.println("Exception thrown : " + e);
        }
        catch (NullPointerException e) {
  
            System.out.println("Exception thrown : " + e);
        }
        catch (NoSuchProviderException 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 KeyFactory
            // and getting instance
            // By using getInstance() method
            KeyFactory sr
                = KeyFactory.getInstance(
                    "RSA", "SUN");
  
            // getting the algorithm of KeyFactory object
            String str = sr.getAlgorithm();
  
            // printing the status
            System.out.println("algorithm : " + str);
        }
  
        catch (NoSuchAlgorithmException e) {
  
            System.out.println("Exception thrown : " + e);
        }
        catch (NullPointerException e) {
  
            System.out.println("Exception thrown : " + e);
        }
        catch (NoSuchProviderException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

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

参考： https://docs.oracle.com/javase/9/docs/api/ Java/security/KeyFactory.html#getInstance-java.lang.String-