<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idelse {
            // 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));
    }