Java 签名 getInstance()方法，带示例
原文:https://www . geesforgeks . org/Java-signature-getinstance-method-with-examples/
字符串算法
java.security.Provider 类的 getInstance() 方法用于返回实现指定签名算法的 Signature 对象。
此方法遍历注册的安全提供程序列表，从最首选的提供程序开始。返回一个新的签名对象，该对象封装了来自支持指定算法的第一个提供程序的签名响应实现。
语法:
public static Signature getInstance(String algorithm)
throws NoSuchAlgorithmException
参数:该方法以算法的标准名称为参数。 返回值:该方法返回新签名对象。 异常:如果没有提供程序支持指定算法的签名实现，此方法将抛出no suchalgorithm Exception。
以下是说明 getInstance() 方法的示例:
例 1:
Java 语言(一种计算机语言，尤用于创建网站)
// 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 Signature and getting instance
// By using getInstance() method
Signature sr = Signature.getInstance("SHA1WithRSA");
// getting the status of signature object
String str = sr.toString();
// printing the status
System.out.println("Status : " + str);
}
catch (NoSuchAlgorithmException e) {
System.out.println("Exception thrown : " + e);
}
catch (ProviderException e) {
System.out.println("Exception thrown : " + e);
}
}
}
Output:
Status : Signature object: SHA1WithRSA
示例 2: 显示 NoSuchAlgorithmException 异常
Java 语言(一种计算机语言，尤用于创建网站)
// 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 Signature and getting instance
// By using getInstance() method
System.out.println("Trying to get the instance of unknown instance");
Signature sr = Signature.getInstance("TAJMAHAL");
// getting the status of signature object
String str = sr.toString();
// printing the status
System.out.println("Status : " + str);
}
catch (NoSuchAlgorithmException e) {
System.out.println("Exception thrown : " + e);
}
catch (ProviderException e) {
System.out.println("Exception thrown : " + e);
}
}
}
Output:
Trying to get the instance of unknown instance
Exception thrown : java.security.NoSuchAlgorithmException: TAJMAHAL Signature not available
签名实例(字符串算法，提供程序提供程序)
java.security.Provider 类的 getInstance() 方法用于返回实现指定签名算法的 Signature 对象。
返回一个新的签名对象，该对象封装了来自指定提供程序对象的签名。请注意，指定的提供程序对象不必在提供程序列表中注册。
语法:
public static Signature
getInstance(String algorithm, Provider provider)
throws NoSuchAlgorithmException
参数:该方法将以下参数作为参数:
- 算法–请求的算法名称。
- 提供商–提供商
返回值:该方法返回新签名对象。
异常:该方法抛出以下异常:
- no suchalgorithm exception–如果指定提供程序对象中没有指定算法的 SignatureSpi 实现。
- IllegalArgumentException–如果提供程序为空。
以下是说明 getInstance() 方法的示例:
例 1:
Java 语言(一种计算机语言，尤用于创建网站)
// 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 Signature and getting instance
// By using getInstance() method
Signature sr = Signature.getInstance("SHA1WithRSA");
// creating Provider object
Provider pd = sr.getProvider();
// getting algorithm name
// by using getAlgorithm() method
String algo = sr.getAlgorithm();
// creating the object of Signature and getting instance
// By using getInstance() method
Signature sr1 = Signature.getInstance(algo, pd);
// getting the status of signature object
String str = sr1.toString();
// printing the status
System.out.println("Status : " + str);
}
catch (NoSuchAlgorithmException e) {
System.out.println("Exception thrown : " + e);
}
catch (ProviderException e) {
System.out.println("Exception thrown : " + e);
}
}
}
Output:
Status : Signature object: SHA1WithRSA
示例 2: 显示 NoSuchAlgorithmException 异常
Java 语言(一种计算机语言，尤用于创建网站)
// 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 Signature and getting instance
// By using getInstance() method
Signature sr = Signature.getInstance("SHA1WithRSA");
// creating Provider object
Provider pd = sr.getProvider();
// getting algorithm name
// by using getAlgorithm() method
String algo = sr.getAlgorithm();
// creating the object of Signature and getting instance
// By using getInstance() method
Signature sr1 = Signature.getInstance("TAJMAHAL", pd);
// getting the status of signature object
String str = sr1.toString();
// printing the status
System.out.println("Status : " + str);
}
catch (NoSuchAlgorithmException e) {
System.out.println("Exception thrown : " + e);
}
catch (ProviderException e) {
System.out.println("Exception thrown : " + e);
}
}
}
Output:
Exception thrown : java.security.NoSuchAlgorithmException: no such algorithm: TAJMAHAL for provider SunRsaSign
示例 3: 显示 IllegalArgumentException
Java 语言(一种计算机语言，尤用于创建网站)
// 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 Signature and getting instance
// By using getInstance() method
Signature sr = Signature.getInstance("SHA1WithRSA");
// creating Provider object
Provider pd = null;
// getting algorithm name
// by using getAlgorithm() method
String algo = sr.getAlgorithm();
// creating the object of Signature and getting instance
// By using getInstance() method
Signature sr1 = Signature.getInstance(algo, pd);
// getting the status of signature object
String str = sr1.toString();
// printing the status
System.out.println("Status : " + str);
}
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);
}
}
}
Output:
Exception thrown : java.lang.IllegalArgumentException: missing provider
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