通过观察，我们发现算法的类型，基本都对应java的一个类。算法类基本在jce.jar和rt.jar中。从这个结果中我们基本就能自己找算法了，比如要用MD5，在上面列表中发现类型是MessageDigest，则
MessageDigest md5 = MessageDigest.getInstance("MD5");再仔细查看java.security.Provider类源码，发现此类在初始时就已经将这些算法类型初始化了，
static
{
addEngine("AlgorithmParameterGenerator", false, null);
addEngine("AlgorithmParameters", false, null);
addEngine("KeyFactory", false, null);
addEngine("KeyPairGenerator", false, null);
addEngine("KeyStore", false, null);
addEngine("MessageDigest", false, null);
addEngine("SecureRandom", false, null);
addEngine("Signature", true, null);
addEngine("CertificateFactory", false, null);
addEngine("CertPathBuilder", false, null);
addEngine("CertPathValidator", false, null);
addEngine("CertStore", false, "java.security.cert.CertStoreParameters");
addEngine("Cipher", true, null);
addEngine("ExemptionMechanism", false, null);
addEngine("Mac", true, null);
addEngine("KeyAgreement", true, null);
addEngine("KeyGenerator", false, null);
addEngine("SecretKeyFactory", false, null);
addEngine("KeyManagerFactory", false, null);
addEngine("SSLContext", false, null);
addEngine("TrustManagerFactory", false, null);
addEngine("GssApiMechanism", false, null);
addEngine("SaslClientFactory", false, null);
addEngine("SaslServerFactory", false, null);
addEngine("Policy", false, "java.security.Policy$Parameters");
addEngine("Configuration", false, "javax.security.auth.login.Configuration$Parameters");
addEngine("XMLSignatureFactory", false, null);
addEngine("KeyInfoFactory", false, null);
addEngine("TransformService", false, null);
addEngine("TerminalFactory", false, "java.lang.Object");
}
//还对大小写做了容错处理
private static void addEngine(String paramString1, boolean paramBoolean, String paramString2)
{
EngineDescription localEngineDescription = new EngineDescription(paramString1, paramBoolean, paramString2);
knownEngines.put(paramString1.toLowerCase(Locale.ENGLISH), localEngineDescription);
knownEngines.put(paramString1, localEngineDescription);
}