<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">

        <property name="entityManagerFactory" ref="entityManagerFactory" />

    </bean>

    /**

     * Generate a bean name for the given bean definition.

     * 根据给定的bean definition 生成一个bean的名字

     * @param definition the bean definition to generate a name for

     * @param 参数 definition 需要生成bean name的BeanDefinition实例

     * @param registry the bean definition registry that the given definition

     * is supposed to be registered with

     * @param 参数registry 是 definition 注册

     * @return the generated bean name

     * @return 返回生成的bean name

     */

    String generateBeanName(BeanDefinition definition, BeanDefinitionRegistry registry);

    /**

     * Generate a bean name for the given top-level bean definition,

     * unique within the given bean factory.

     * @param beanDefinition the bean definition to generate a bean name for

     * @param registry the bean factory that the definition is going to be

     * registered with (to check for existing bean names)

     * @return the generated bean name

     * @throws BeanDefinitionStoreException if no unique name can be generated

     * for the given bean definition

     */

    public static String generateBeanName(BeanDefinition beanDefinition, BeanDefinitionRegistry registry)

            throws BeanDefinitionStoreException {

        return generateBeanName(beanDefinition, registry, false);

    }

/**

     * Generate a bean name for the given bean definition, unique within the

     * given bean factory.

     * @param definition the bean definition to generate a bean name for

     * @param registry the bean factory that the definition is going to be

     * registered with (to check for existing bean names)

     * @param isInnerBean whether the given bean definition will be registered

     * as inner bean or as top-level bean (allowing for special name generation

     * for inner beans versus top-level beans)

     * @param isInnerBean  参数definition会被注册为一个内部bean还是一个顶级bean(内部bean和顶级bean 都允许使用特殊名字定义）

     * @return the generated bean name

     * @throws BeanDefinitionStoreException if no unique name can be generated

     * for the given bean definition

     * @throws BeanDefinitionStoreException 当没有唯一的名称可供生成的时候抛出异常

     */

    public static String generateBeanName(

            BeanDefinition definition, BeanDefinitionRegistry registry, boolean isInnerBean)

            throws BeanDefinitionStoreException {

        //generatedBeanName定义为类前缀， 读取bean的className,不一定是运行时的实际类型。

        String generatedBeanName = definition.getBeanClassName();

        if (generatedBeanName == null) {

            //如果类名称为空，那读取bean的parent bean name

            if (definition.getParentName() != null) {

                generatedBeanName = definition.getParentName() + "$child";

            }

            //否则，读取生成该bean的factoryBean name名称做前缀。

            else if (definition.getFactoryBeanName() != null) {

                generatedBeanName = definition.getFactoryBeanName() + "$created";

            }

        }

        //generatedBeanName为空字符串，抛出异常

        if (!StringUtils.hasText(generatedBeanName)) {

            throw new BeanDefinitionStoreException("Unnamed bean definition specifies neither " +

                    "'class' nor 'parent' nor 'factory-bean' - can't generate bean name");

        }

        String id = generatedBeanName;

        //当为内部bean时，调用系统底层的object唯一标识码生成

        if (isInnerBean) {

            // Inner bean: generate identity hashcode suffix.

            id = generatedBeanName + GENERATED_BEAN_NAME_SEPARATOR + ObjectUtils.getIdentityHexString(definition);

        }

        //否则即为顶级bean，生成策略是前缀+循环数字，直到找到对应自增id

        else {

            // Top-level bean: use plain class name.

            // Increase counter until the id is unique.

            int counter = -1;

            while (counter == -1 || registry.containsBeanDefinition(id)) {

                counter++;

                id = generatedBeanName + GENERATED_BEAN_NAME_SEPARATOR + counter;

            }

        }

        return id;

    }

//    ObjectUtils.java

    /**

     * Return a hex String form of an object's identity hash code.

     * 返回一个十六进制数从hash code中获得

     * @param obj

     *            the object

     * @return the object's identity code in hex notation

     */

    public static String getIdentityHexString(Object obj) {

        return Integer.toHexString(System.identityHashCode(obj));

    }

    //    System.java

    /**

     * Returns the same hash code for the given object as would be returned by

     * the default method hashCode(), whether or not the given object's class

     * overrides hashCode(). The hash code for the null reference is zero.

     *

     * @param x

     *            object for which the hashCode is to be calculated

     * @return the hashCode

     * @since JDK1.1

     */

    //native 表示操作系统实现的底层框架，用于生成对象的hashcode。jvm的实现还没有关心。

    public static native int identityHashCode(Object x);

    //  Integer.java

    /**

     * All possible chars for representing a number as a String

     */

    final static char[] digits = { '0', '1', '2', '3', '4', '5', '6', '7', '8',

            '9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l',

            'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y',

            'z' };

    public static String toHexString(int i) {

        return toUnsignedString(i, 4);

    }

    private static String toUnsignedString(int i, int shift) {

        char[] buf = new char[32];

        int charPos = 32;

        int radix = 1 << shift;

        int mask = radix - 1;

        do {

            buf[--charPos] = digits[i & mask];

            i >>>= shift;

        } while (i != 0);

        return new String(buf, charPos, (32 - charPos));

    }