Java KeyPairGenerator getInstance()用法及代碼示例

getInstance(String algorithm)

java.security.KeyPairGenerator類的getInstance()方法用於返回KeyPairGenerator對象，該對象為指定算法生成公用/專用 key 對。

此方法從最喜歡的提供者開始遍曆已注冊的安全提供者列表。返回一個新的KeyPairGenerator對象，該對象封裝了支持指定算法的第一個Provider的KeyPairGeneratorSpi實現。

用法:

public static KeyPairGenerator 
    getInstance(String algorithm)
        throws NoSuchAlgorithmException

參數：此方法將“算法”的標準名稱作為參數。

返回值：此方法返回新的KeyPairGenerator對象。

異常：如果沒有提供者支持指定算法的Signature實現，則此方法將引發NoSuchAlgorithmException。

下麵是說明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); 
        } 
    } 
}

Algorithm : DSA

示例2:顯示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); 
        } 
    } 
}

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

getInstance(String algorithm, Provider provider)

java.security.KeyPairGenerator類的getInstance()方法用於返回KeyPairGenerator對象，該對象為指定算法生成公用/專用 key 對。
返回一個新的KeyPairGenerator對象，該對象封裝了來自指定Provider對象的KeyPairGeneratorSpi實現。請注意，指定的提供程序對象不必在提供程序列表中注冊。

用法:

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

參數：此方法將以下參數作為參數：

• algorithm：請求的算法的名稱。
• provider:提供者

返回值：此方法返回新的KeyPairGenerator對象。

異常：此方法引發以下異常：

• NoSuchAlgorithmException –如果指定的Provider對象不提供指定算法的SignatureSpi實現。
• IllegalArgumentException –如果提供者為null。

下麵是說明getInstance()方法的示例：

注意：以下程序將無法在在線IDE上運行。

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); 
        } 
    } 
}
輸出：

Keypair : java.security.KeyPair@12a3a380

示例2:顯示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); 
        } 
    } 
}

輸出：

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

示例3:顯示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); 
        } 
    } 
}

輸出：

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