Java中的 AlgorithmParameterGenerator getInstance() 方法及示例

getInstance(字符串算法)

Java.security.AlgorithmParameterGenerator 类的getInstance()方法用于返回实现指定算法的AlgorithmParameterGenerator 类型的对象。
句法：

public static AlgorithmParameterGenerator 
  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 AlgorithmParameterGenerator 对象。
异常：此方法抛出以下异常：

• NoSuchAlgorithmException：如果没有 Provider 支持指定算法的 AlgorithmParameterGeneratorSpi 实现。
• NullPointerException：如果指定的算法为空。

下面是说明getInstance()方法的示例：
示例 1：

Java

// Java program to demonstrate
// getInstance() method
 
import java.security.*;
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
            // Getting instance of
            // AlgorithmParameterGenerator
            // By using getInstance() method
            AlgorithmParameterGenerator sr
                = AlgorithmParameterGenerator
                      .getInstance("DSA");
 
            // getting the status of
            // AlgorithmParameterGenerator object
            String str = sr.toString();
 
            // printing the status
            System.out.println("Status: "
                               + str);
        }
 
        catch (NoSuchAlgorithmException e) {
 
            System.out.println("Exception thrown: "
                               + e);
        }
        catch (NullPointerException e) {
 
            System.out.println("Exception thrown: "
                               + e);
        }
    }
}

输出：

Status: java.security.AlgorithmParameterGenerator@232204a1

示例 2：显示 NoSuchAlgorithmException

Java

// Java program to demonstrate
// getInstance() method
 
import java.security.*;
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
            // Getting instance of
            // AlgorithmParameterGenerator
            // By using getInstance() method
            AlgorithmParameterGenerator sr
                = AlgorithmParameterGenerator
                      .getInstance("GFG");
 
            // getting the status of
            // AlgorithmParameterGenerator object
            String str = sr.toString();
 
            // printing the status
            System.out.println("Status: " + 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:
 GFG AlgorithmParameterGenerator not available

签名getInstance（字符串算法，Provider提供者）

Java.security.AlgorithmParameterGenerator 类的getInstance()方法用于返回一个AlgorithmParameterGenerator 对象，该对象实现了指定的签名算法和指定的provider 对象。
句法：

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

参数：此方法将以下参数作为参数：

• algorithm ：这是请求的算法的名称。
• provider : 指定的提供者

返回值：此方法返回新的 AlgorithmParameterGenerator 对象。
异常：此方法抛出以下异常：

• NoSuchAlgorithmException：如果指定算法的 AlgorithmParameterGeneratorSpi 实现不能从指定的 Provider 对象获得。
• 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

// Java program to demonstrate
// getInstance() method
 
import java.security.*;
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
            // Getting instance of
            // AlgorithmParameterGenerator
            // By using getInstance() method
            AlgorithmParameterGenerator sr
                = AlgorithmParameterGenerator
                      .getInstance("DSA");
 
            // creating Provider object
            Provider pd = sr.getProvider();
 
            // getting algorithm name
            // by using getAlgorithm() method
            String algo = sr.getAlgorithm();
 
            // Getting instance of
            // AlgorithmParameterGenerator
            // By using getInstance() method
            AlgorithmParameterGenerator sr1
                = AlgorithmParameterGenerator
                      .getInstance(algo, pd);
 
            // getting the status of
            // AlgorithmParameterGenerator object
            String str = sr1.toString();
 
            // printing the status
            System.out.println("Status: "
                               + str);
        }
 
        catch (NoSuchAlgorithmException e) {
 
            System.out.println("Exception thrown: "
                               + e);
        }
        catch (IllegalArgumentException e) {
 
            System.out.println("Exception thrown: "
                               + e);
        }
    }
}

输出：

Status: java.security.AlgorithmParameterGenerator@232204a1

示例 2：显示 NoSuchAlgorithmException

Java

// Java program to demonstrate
// getInstance() method
 
import java.security.*;
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
    {
        try {
            // Getting instance of
            // AlgorithmParameterGenerator
            // By using getInstance() method
            AlgorithmParameterGenerator sr
                = AlgorithmParameterGenerator
                      .getInstance("GFG");
 
            // creating Provider object
            Provider pd = sr.getProvider();
 
            // getting algorithm name
            // by using getAlgorithm() method
            String algo = sr.getAlgorithm();
 
            // Getting instance of
            // AlgorithmParameterGenerator
            // By using getInstance() method
            AlgorithmParameterGenerator sr1
                = AlgorithmParameterGenerator
                      .getInstance(algo, pd);
 
            // getting the status of
            // AlgorithmParameterGenerator object
            String str = sr1.toString();
 
            // printing the status
            System.out.println("Status: " + str);
        }
 
        catch (NoSuchAlgorithmException e) {
 
            System.out.println("Exception thrown: "
                               + e);
        }
        catch (IllegalArgumentException e) {
 
            System.out.println("Exception thrown: "
                               + e);
        }
    }
}

输出：

Exception thrown:
 java.security.NoSuchAlgorithmException:
 GFG AlgorithmParameterGenerator not available

参考：

• https://docs.oracle.com/javase/9/docs/api/ Java/security/AlgorithmParameterGenerator.html#getInstance-java.lang.String-
• https://docs.oracle.com/javase/9/docs/api/ Java/security/AlgorithmParameterGenerator.html#getInstance-java.lang.String-java.security.Provider-