这里只说ImprovedNamingStrategy，其他自行看Hibernate代码，ImprovedNamingStrategy的代码如下，是一个singleton instance：

/*
* Hibernate, Relational Persistence for Idiomatic Java
*
* Copyright (c) 2010, Red Hat Inc. or third-party contributors as
* indicated by the @author tags or express copyright attribution
* statements applied by the authors.  All third-party contributions are
* distributed under license by Red Hat Inc.
*
* This copyrighted material is made available to anyone wishing to use, modify,
* copy, or redistribute it subject to the terms and conditions of the GNU
* Lesser General Public License, as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
* for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this distribution; if not, write to:
* Free Software Foundation, Inc.
* 51 Franklin Street, Fifth Floor
* Boston, MA  02110-1301  USA
*/
package org.hibernate.cfg;

import java.io.Serializable;

import org.hibernate.util.StringHelper;
import org.hibernate.AssertionFailure;

/**
* An improved naming strategy that prefers embedded
* underscores to mixed case names
* @see DefaultNamingStrategy the default strategy
* @author Gavin King
*/
public class ImprovedNamingStrategy implements NamingStrategy, Serializable {

/**
 * A convenient singleton instance
 */
public static final NamingStrategy INSTANCE = new ImprovedNamingStrategy();

/**
 * Return the unqualified class name, mixed case converted to
 * underscores
 */
public String classToTableName(String className) {
    return addUnderscores( StringHelper.unqualify(className) );
}
/**
 * Return the full property path with underscore seperators, mixed
 * case converted to underscores
 */
public String propertyToColumnName(String propertyName) {
    return addUnderscores( StringHelper.unqualify(propertyName) );
}
/**
 * Convert mixed case to underscores
 */
public String tableName(String tableName) {
    return addUnderscores(tableName);
}
/**
 * Convert mixed case to underscores
 */
public String columnName(String columnName) {
    return addUnderscores(columnName);
}

protected static String addUnderscores(String name) {
    StringBuffer buf = new StringBuffer( name.replace('.', '_') );
    for (int i=1; i<buf.length()-1; i++) {
        if (
            Character.isLowerCase( buf.charAt(i-1) ) &&
            Character.isUpperCase( buf.charAt(i) ) &&
            Character.isLowerCase( buf.charAt(i+1) )
        ) {
            buf.insert(i++, '_');
        }
    }
    return buf.toString().toLowerCase();
}

public String collectionTableName(
        String ownerEntity, String ownerEntityTable, String associatedEntity, String associatedEntityTable,
        String propertyName
) {
    return tableName( ownerEntityTable + '_' + propertyToColumnName(propertyName) );
}

/**
 * Return the argument
 */
public String joinKeyColumnName(String joinedColumn, String joinedTable) {
    return columnName( joinedColumn );
}

/**
 * Return the property name or propertyTableName
 */
public String foreignKeyColumnName(
        String propertyName, String propertyEntityName, String propertyTableName, String referencedColumnName
) {
    String header = propertyName != null ? StringHelper.unqualify( propertyName ) : propertyTableName;
    if (header == null) throw new AssertionFailure("NamingStrategy not properly filled");
    return columnName( header ); //+ "_" + referencedColumnName not used for backward compatibility
}

/**
 * Return the column name or the unqualified property name
 */
public String logicalColumnName(String columnName, String propertyName) {
    return StringHelper.isNotEmpty( columnName ) ? columnName : StringHelper.unqualify( propertyName );
}

/**
 * Returns either the table name if explicit or
 * if there is an associated table, the concatenation of owner entity table and associated table
 * otherwise the concatenation of owner entity table and the unqualified property name
 */
public String logicalCollectionTableName(String tableName,
                                         String ownerEntityTable, String associatedEntityTable, String propertyName
) {
    if ( tableName != null ) {
        return tableName;
    }
    else {
        //use of a stringbuffer to workaround a JDK bug
        return new StringBuffer(ownerEntityTable).append("_")
                .append(
                    associatedEntityTable != null ?
                    associatedEntityTable :
                    StringHelper.unqualify( propertyName )
                ).toString();
    }
}
/**
 * Return the column name if explicit or the concatenation of the property name and the referenced column
 */
public String logicalCollectionColumnName(String columnName, String propertyName, String referencedColumn) {
    return StringHelper.isNotEmpty( columnName ) ?
            columnName :
            StringHelper.unqualify( propertyName ) + "_" + referencedColumn;
}
}

<prop key="hibernate.ejb.naming_strategy">org.hibernate.cfg.ImprovedNamingStrategy</prop>

/*
* Copyright 2012-2014 sencloud.com.cn. All rights reserved.
* Support: http://www.sencloud.com.cn
* License: http://www.sencloud.com.cn/license
*/
package com.sencloud.hibernate.cfg;

import java.io.Serializable;

import org.hibernate.cfg.ImprovedNamingStrategy;
import org.hibernate.cfg.NamingStrategy;
import org.hibernate.util.StringHelper;

/**
* ImprovedNamingStrategy－ hibernate映射规则
* 
* @author xutianlong
* @version 3.0
*/
public class MoShopImprovedNamingStrategy extends ImprovedNamingStrategy
    implements NamingStrategy, Serializable {
/**
 * 
 */
private static final long serialVersionUID = 3088474161734101900L;

public String propertyToColumnName(String propertyName) {
    if (propertyName.endsWith("__")) {
        return propertyName.replace("__", "").toLowerCase();
    }
    return addUnderscores(StringHelper.unqualify(propertyName));
}
}

<prop key="hibernate.ejb.naming_strategy">com.sencloud.hibernate.cfg.MoShopImprovedNamingStrategy</prop>

@Column(nullable = false, length=100)
private String userName__;