exceptionfactory commented on a change in pull request #3890:
URL: https://github.com/apache/nifi/pull/3890#discussion_r803030400



##########
File path: 
nifi-nar-bundles/nifi-standard-services/nifi-dbcp-service-bundle/nifi-dbcp-service/src/main/java/org/apache/nifi/dbcp/HikariCPConnectionPool.java
##########
@@ -0,0 +1,362 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.nifi.dbcp;
+
+import com.zaxxer.hikari.HikariDataSource;
+import org.apache.commons.lang3.StringUtils;
+import org.apache.nifi.annotation.behavior.DynamicProperty;
+import org.apache.nifi.annotation.behavior.RequiresInstanceClassLoading;
+import org.apache.nifi.annotation.documentation.CapabilityDescription;
+import org.apache.nifi.annotation.documentation.Tags;
+import org.apache.nifi.annotation.lifecycle.OnDisabled;
+import org.apache.nifi.annotation.lifecycle.OnEnabled;
+import org.apache.nifi.components.PropertyDescriptor;
+import org.apache.nifi.components.PropertyValue;
+import org.apache.nifi.components.resource.ResourceCardinality;
+import org.apache.nifi.components.resource.ResourceType;
+import org.apache.nifi.controller.AbstractControllerService;
+import org.apache.nifi.controller.ConfigurationContext;
+import org.apache.nifi.expression.AttributeExpression;
+import org.apache.nifi.expression.ExpressionLanguageScope;
+import org.apache.nifi.kerberos.KerberosUserService;
+import org.apache.nifi.processor.exception.ProcessException;
+import org.apache.nifi.processor.util.StandardValidators;
+import org.apache.nifi.security.krb.KerberosAction;
+import org.apache.nifi.security.krb.KerberosUser;
+
+import javax.security.auth.login.LoginException;
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Properties;
+import java.util.concurrent.TimeUnit;
+import java.util.stream.Collectors;
+
+/**
+ * Implementation of Database Connection Pooling Service. HikariCP is used for 
connection pooling functionality.
+ */
+@RequiresInstanceClassLoading
+@Tags({"dbcp", "hikari", "jdbc", "database", "connection", "pooling", "store"})
+@CapabilityDescription("Provides Database Connection Pooling Service based on 
HikariCP. Connections can be asked from pool and returned after usage.")
+@DynamicProperty(name = "JDBC property name", value = "JDBC property value", 
expressionLanguageScope = ExpressionLanguageScope.VARIABLE_REGISTRY,
+        description = "Specifies a property name and value to be set on the 
JDBC connection(s). "
+                + "If Expression Language is used, evaluation will be 
performed upon the controller service being enabled. "
+                + "Note that no flow file input (attributes, e.g.) is 
available for use in Expression Language constructs for these properties.")
+public class HikariCPConnectionPool extends AbstractControllerService 
implements DBCPService {
+    /**
+     * Property Name Prefix for Sensitive Dynamic Properties
+     */
+    protected static final String SENSITIVE_PROPERTY_PREFIX = "SENSITIVE.";
+    protected static final long INFINITE_MILLISECONDS = -1L;
+
+    private static final String DEFAULT_TOTAL_CONNECTIONS = "10";
+    private static final String DEFAULT_MAX_CONN_LIFETIME = "-1";
+
+    public static final PropertyDescriptor DATABASE_URL = new 
PropertyDescriptor.Builder()
+            .name("hikaricp-connection-url")
+            .displayName("Database Connection URL")
+            .description("A database connection URL used to connect to a 
database. May contain database system name, host, port, database name and some 
parameters."
+                    + " The exact syntax of a database connection URL is 
specified by your DBMS.")
+            .defaultValue(null)
+            .addValidator(StandardValidators.NON_EMPTY_VALIDATOR)
+            .required(true)
+            
.expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY)
+            .build();
+
+    public static final PropertyDescriptor DB_DRIVERNAME = new 
PropertyDescriptor.Builder()
+            .name("hikaricp-driver-classname")
+            .displayName("Database Driver Class Name")
+            .description("The fully-qualified class name of the JDBC driver. 
Example: com.mysql.jdbc.Driver")
+            .defaultValue(null)
+            .required(true)
+            .addValidator(StandardValidators.NON_EMPTY_VALIDATOR)
+            
.expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY)
+            .build();
+
+    public static final PropertyDescriptor DB_DRIVER_LOCATION = new 
PropertyDescriptor.Builder()
+            .name("hikaricp-driver-locations")
+            .displayName("Database Driver Location(s)")
+            .description("Comma-separated list of files/folders and/or URLs 
containing the driver JAR and its dependencies (if any). For example 
'/var/tmp/mariadb-java-client-1.1.7.jar'")
+            .defaultValue(null)
+            .required(false)
+            .identifiesExternalResource(ResourceCardinality.MULTIPLE, 
ResourceType.FILE, ResourceType.DIRECTORY, ResourceType.URL)
+            
.expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY)
+            .dynamicallyModifiesClasspath(true)
+            .build();
+
+    public static final PropertyDescriptor DB_USER = new 
PropertyDescriptor.Builder()
+            .name("hikaricp-username")
+            .displayName("Database User")
+            .description("Database user name")
+            .defaultValue(null)
+            .addValidator(StandardValidators.NON_EMPTY_VALIDATOR)
+            
.expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY)
+            .build();
+
+    public static final PropertyDescriptor DB_PASSWORD = new 
PropertyDescriptor.Builder()
+            .name("hikaricp-password")
+            .displayName("Password")
+            .description("The password for the database user")
+            .defaultValue(null)
+            .required(false)
+            .sensitive(true)
+            .addValidator(StandardValidators.NON_EMPTY_VALIDATOR)
+            
.expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY)
+            .build();
+
+    public static final PropertyDescriptor MAX_WAIT_TIME = new 
PropertyDescriptor.Builder()
+            .name("hikaricp-max-wait-time")
+            .displayName("Max Wait Time")
+            .description("The maximum amount of time that the pool will wait 
(when there are no available connections) "
+                    + " for a connection to be returned before failing, or 0 
<time units> to wait indefinitely. ")
+            .defaultValue("500 millis")
+            .required(true)
+            .addValidator(StandardValidators.TIME_PERIOD_VALIDATOR)
+            .sensitive(false)
+            
.expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY)
+            .build();
+
+    public static final PropertyDescriptor MAX_TOTAL_CONNECTIONS = new 
PropertyDescriptor.Builder()
+            .name("hikaricp-max-total-conns")
+            .displayName("Max Total Connections")
+            .description("This property controls the maximum size that the 
pool is allowed to reach, including both idle and in-use connections. Basically 
this value will determine the "
+                    + "maximum number of actual connections to the database 
backend. A reasonable value for this is best determined by your execution 
environment. When the pool reaches "
+                    + "this size, and no idle connections are available, the 
service will block for up to connectionTimeout milliseconds before timing out.")
+            .defaultValue(DEFAULT_TOTAL_CONNECTIONS)
+            .required(true)
+            .addValidator(StandardValidators.INTEGER_VALIDATOR)
+            .sensitive(false)
+            
.expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY)
+            .build();
+
+    public static final PropertyDescriptor VALIDATION_QUERY = new 
PropertyDescriptor.Builder()
+            .name("hikaricp-validation-query")
+            .displayName("Validation Query")
+            .description("Validation Query used to validate connections before 
returning them. "
+                    + "When connection is invalid, it gets dropped and new 
valid connection will be returned. "
+                    + "NOTE: Using validation might have some performance 
penalty.")
+            .required(false)
+            .addValidator(StandardValidators.NON_EMPTY_VALIDATOR)
+            
.expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY)
+            .build();
+
+    public static final PropertyDescriptor MIN_IDLE = new 
PropertyDescriptor.Builder()
+            .name("hikaricp-min-idle-conns")
+            .displayName("Minimum Idle Connections")
+            .description("This property controls the minimum number of idle 
connections that HikariCP tries to maintain in the pool. If the idle 
connections dip below this value and total "
+                    + "connections in the pool are less than 'Max Total 
Connections', HikariCP will make a best effort to add additional connections 
quickly and efficiently. It is recommended "
+                    + "that this property to be set equal to 'Max Total 
Connections'.")
+            .defaultValue(DEFAULT_TOTAL_CONNECTIONS)
+            .required(true)
+            .addValidator(StandardValidators.NON_NEGATIVE_INTEGER_VALIDATOR)
+            
.expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY)
+            .build();
+
+    public static final PropertyDescriptor MAX_CONN_LIFETIME = new 
PropertyDescriptor.Builder()
+            .name("hikaricp-max-conn-lifetime")
+            .displayName("Max Connection Lifetime")
+            .description("The maximum lifetime in milliseconds of a 
connection. After this time is exceeded the " +
+                    "connection will fail the next activation, passivation or 
validation test. A value of zero or less " +
+                    "means the connection has an infinite lifetime.")
+            .defaultValue(DEFAULT_MAX_CONN_LIFETIME)
+            .required(false)
+            .addValidator(DBCPValidator.CUSTOM_TIME_PERIOD_VALIDATOR)
+            
.expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY)
+            .build();
+
+    public static final PropertyDescriptor KERBEROS_USER_SERVICE = new 
PropertyDescriptor.Builder()
+            .name("hikaricp-kerberos-user-service")
+            .displayName("Kerberos User Service")
+            .description("Specifies the Kerberos User Controller Service that 
should be used for authenticating with Kerberos")
+            .identifiesControllerService(KerberosUserService.class)
+            .required(false)
+            .build();
+
+    private static final List<PropertyDescriptor> properties;
+
+    static {
+        final List<PropertyDescriptor> props = new ArrayList<>();
+        props.add(DATABASE_URL);
+        props.add(DB_DRIVERNAME);
+        props.add(DB_DRIVER_LOCATION);
+        props.add(KERBEROS_USER_SERVICE);
+        props.add(DB_USER);
+        props.add(DB_PASSWORD);
+        props.add(MAX_WAIT_TIME);
+        props.add(MAX_TOTAL_CONNECTIONS);
+        props.add(VALIDATION_QUERY);
+        props.add(MIN_IDLE);
+        props.add(MAX_CONN_LIFETIME);
+
+        properties = Collections.unmodifiableList(props);
+    }
+
+    private volatile HikariDataSource dataSource;
+    private volatile KerberosUser kerberosUser;
+
+    @Override
+    protected List<PropertyDescriptor> getSupportedPropertyDescriptors() {
+        return properties;
+    }
+
+    @Override
+    protected PropertyDescriptor getSupportedDynamicPropertyDescriptor(final 
String propertyDescriptorName) {
+        final PropertyDescriptor.Builder builder = new 
PropertyDescriptor.Builder()
+                .name(propertyDescriptorName)
+                .required(false)
+                .dynamic(true)
+                
.addValidator(StandardValidators.createAttributeExpressionLanguageValidator(AttributeExpression.ResultType.STRING,
 true))
+                
.addValidator(StandardValidators.ATTRIBUTE_KEY_PROPERTY_NAME_VALIDATOR);
+
+        if (propertyDescriptorName.startsWith(SENSITIVE_PROPERTY_PREFIX)) {
+            
builder.sensitive(true).expressionLanguageSupported(ExpressionLanguageScope.NONE);
+        } else {
+            
builder.expressionLanguageSupported(ExpressionLanguageScope.VARIABLE_REGISTRY);
+        }
+
+        return builder.build();
+    }
+
+    /**
+     * Configures connection pool by creating an instance of the
+     * {@link HikariDataSource} based on configuration provided with
+     * {@link ConfigurationContext}.
+     * <p>
+     * This operation makes no guarantees that the actual connection could be
+     * made since the underlying system may still go off-line during normal
+     * operation of the connection pool.
+     *
+     * @param context the configuration context
+     */
+    @OnEnabled
+    public void onConfigured(final ConfigurationContext context) {
+
+        final String driverName = 
context.getProperty(DB_DRIVERNAME).evaluateAttributeExpressions().getValue();
+        final String user = 
context.getProperty(DB_USER).evaluateAttributeExpressions().getValue();
+        final String passw = 
context.getProperty(DB_PASSWORD).evaluateAttributeExpressions().getValue();
+        final String dburl = 
context.getProperty(DATABASE_URL).evaluateAttributeExpressions().getValue();
+        final Integer maxTotal = 
context.getProperty(MAX_TOTAL_CONNECTIONS).evaluateAttributeExpressions().asInteger();
+        final String validationQuery = 
context.getProperty(VALIDATION_QUERY).evaluateAttributeExpressions().getValue();
+        final long maxWaitMillis = 
extractMillisWithInfinite(context.getProperty(MAX_WAIT_TIME).evaluateAttributeExpressions());
+        final int minIdle = 
context.getProperty(MIN_IDLE).evaluateAttributeExpressions().asInteger();
+        final long maxConnLifetimeMillis = 
extractMillisWithInfinite(context.getProperty(MAX_CONN_LIFETIME).evaluateAttributeExpressions());
+        final KerberosUserService kerberosUserService = 
context.getProperty(KERBEROS_USER_SERVICE).asControllerService(KerberosUserService.class);
+
+        if (kerberosUserService != null) {
+            kerberosUser = kerberosUserService.createKerberosUser();
+            if (kerberosUser != null) {
+                kerberosUser.login();
+            }
+        }
+
+        dataSource = new HikariDataSource();
+        dataSource.setDriverClassName(driverName);
+        dataSource.setConnectionTimeout(maxWaitMillis);
+        dataSource.setMaximumPoolSize(maxTotal);
+        dataSource.setMinimumIdle(minIdle);
+        dataSource.setMaxLifetime(maxConnLifetimeMillis);
+
+        if (validationQuery != null && !validationQuery.isEmpty()) {
+            dataSource.setConnectionTestQuery(validationQuery);
+        }
+
+        dataSource.setJdbcUrl(dburl);
+        dataSource.setUsername(user);
+        dataSource.setPassword(passw);
+
+        final List<PropertyDescriptor> dynamicProperties = 
context.getProperties()
+                .keySet()
+                .stream()
+                .filter(PropertyDescriptor::isDynamic)
+                .collect(Collectors.toList());
+
+        Properties properties = dataSource.getDataSourceProperties();
+        dynamicProperties.forEach((descriptor) -> {
+            final PropertyValue propertyValue = 
context.getProperty(descriptor);
+            if (descriptor.isSensitive()) {
+                final String propertyName = 
StringUtils.substringAfter(descriptor.getName(), SENSITIVE_PROPERTY_PREFIX);
+                properties.setProperty(propertyName, propertyValue.getValue());
+            } else {
+                properties.setProperty(descriptor.getName(), 
propertyValue.evaluateAttributeExpressions().getValue());
+            }
+        });
+        dataSource.setDataSourceProperties(properties);
+
+    }
+
+    private long extractMillisWithInfinite(PropertyValue prop) {
+        return "-1".equals(prop.getValue()) ? INFINITE_MILLISECONDS : 
prop.asTimePeriod(TimeUnit.MILLISECONDS);
+    }
+
+    /**
+     * Shutdown pool, close all open connections.
+     * If a principal is authenticated with a KDC, that principal is logged 
out.
+     * <p>
+     * If a @{@link LoginException} occurs while attempting to log out the 
@{@link org.apache.nifi.security.krb.KerberosUser},
+     * an attempt will still be made to shut down the pool and close open 
connections.
+     *
+     */
+    @OnDisabled
+    public void shutdown() {
+        try {
+            if (kerberosUser != null) {
+                kerberosUser.logout();
+            }
+        } finally {
+            kerberosUser = null;
+            try {
+                if (dataSource != null) {
+                    dataSource.close();
+                }
+            } finally {
+                dataSource = null;
+            }
+        }
+    }
+
+    @Override
+    public Connection getConnection() throws ProcessException {
+        try {
+            final Connection con;
+            if (kerberosUser != null) {
+                KerberosAction<Connection> kerberosAction = new 
KerberosAction<>(kerberosUser, () -> dataSource.getConnection(), getLogger());
+                con = kerberosAction.execute();
+            } else {
+                con = dataSource.getConnection();
+            }
+            return con;
+        } catch (final SQLException e) {
+            // If using Kerberos,  attempt to re-login
+            if (kerberosUser != null) {

Review comment:
       Thanks for the reply, makes sense under the circumstances.




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