Java MessageDigest getInstance()用法及代碼示例

getInstance(String algorithm)

java.security.MessageDigest類的getInstance()方法用於返回MessageDigest類型的對象，該對象應用分配的MessageDigest算法。

用法:

public static MessageDigest
  getInstance(String algorithm)
  throws NoSuchAlgorithmException

參數：此方法接受標準算法的名稱作為參數。

返回值：此方法提供了MessageDigest類型的對象。

異常：此方法引發以下異常：

NoSuchAlgorithmException：如果沒有提供者支持特定算法的消息摘要spi應用程序。
NullPointerException ：如果algorithm為null。

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 MessageDigest 
            // and getting instance 
            // By usng getInstance() method 
            MessageDigest sr 
                = MessageDigest.getInstance("MD5"); 
  
            // getting the status of MessageDigest 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); 
        } 
    } 
}

輸出：

Status : MD5 Message Digest from SUN, <initialized>

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 MessageDigest 
            // and getting instance 
            // By usng getInstance() method 
            MessageDigest sr 
                = MessageDigest.getInstance("GFG"); 
  
            // getting the status of MessageDigest 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); 
        } 
    } 
}

輸出：

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

getInstance(String algorithm, String provider)

java.security.MessageDigest類的此getInstance()方法提供了MessageDigest類型的對象，該對象應用分配的MessageDigest算法和分配的提供程序對象。

用法:

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

參數：此方法尋求以下參數作為參數：

algorithm：是在此實例中要指定的算法的名稱。
provider：這是在此實例中要指定的提供者的名稱

返回值：此方法提供了MessageDigest類型的對象。

異常：此方法引發以下異常：

NoSuchAlgorithmException：–如果特定提供者沒有針對特定算法的MessageDigestSpi實現。
IllegalArgumentException：如果提供者為null。
NullPointerException ：如果算法為空

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 MessageDigest 
            // and getting instance 
            // By usng getInstance() method 
            MessageDigest sr 
                = MessageDigest.getInstance( 
                    "SHA-384", "SUN"); 
  
            // getting the status of MessageDigest 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); 
        } 
        catch (NoSuchProviderException e) { 
  
            System.out.println("Exception thrown : " + e); 
        } 
    } 
}

輸出：

Status : SHA-384 Message Digest from SUN, <initialized>

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 MessageDigest 
            // and getting instance 
            // By usng getInstance() method 
            MessageDigest sr 
                = MessageDigest.getInstance( 
                    "GFG", "SUN"); 
  
            // getting the status of MessageDigest 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); 
        } 
        catch (NoSuchProviderException e) { 
  
            System.out.println("Exception thrown : " + e); 
        } 
    } 
}

輸出：

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

參考： https://docs.oracle.com/javase/9/docs/api/java/security/MessageDigest.html#getInstance-java.lang.String-java.lang.String-

相關用法

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