MongoDB复制指南与Java编码规范

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"MongoDB in Action" 本文将深入探讨MongoDB的复制功能，这是MongoDB数据库系统中的一个关键特性，用于实现数据的高可用性和容错性。MongoDB复制通过创建数据副本来确保数据的安全性和连续性，即使在主节点出现故障时，也能保证服务不中断。 MongoDB的复制过程通常涉及三个主要组件：主节点（Primary）、副节点（Secondary）和仲裁节点（Arbiter）。主节点负责处理所有读写操作，并将更改同步到副节点。副节点是数据的备份，它们接收并应用主节点的日志条目，保持与主节点的数据一致。仲裁节点不存储数据，但在选举新主节点时起决定性作用，确保复制集的稳定运行。复制过程的核心是复制集，它是一组配置为复制的MongoDB实例。复制集内的节点通过心跳检查来监控彼此的状态，并在主节点失效时自动进行主备切换，这个过程称为选举。选举过程中，具有最多完整数据和最近接收到数据更新的副节点将被选为主节点。在实际应用中，MongoDB的复制提供了多种优势。首先，它增强了数据的可靠性，因为数据在多个节点上存在。其次，复制允许进行计划内维护，如硬件升级或软件更新，而不会中断服务。此外，副节点还可以用于读取查询，从而在读密集型应用中提高性能。最后，复制还提供了灾难恢复的能力，因为可以从备份节点恢复数据。配置MongoDB复制需要设置复制集，包括定义初始主节点、副节点和可能的仲裁节点，以及配置复制集参数，如心跳间隔和选举超时。管理员还需要监控复制状态，确保数据同步和复制集的健康运行。为了确保复制的高效运行，开发人员应遵循最佳实践，例如定期检查复制延迟，确保副节点能及时跟上主节点的变更。此外，合理的硬件规划和网络设计也是必要的，以减少延迟并优化数据同步。在开发过程中，遵循像"AmbySoft Inc. Coding Standards for Java"这样的编码标准文档，可以提高代码质量和可维护性，从而间接提升MongoDB复制的稳定性和效率。这些标准强调编写易于理解、维护和增强的代码，遵循良好的软件工程原则，有助于团队协作和生产力的提升。 MongoDB的复制功能是其高可用性架构的关键组成部分，通过复制集、主备切换和选举机制确保了服务的连续性和数据安全。开发者和管理员需要理解复制的工作原理，掌握配置和管理复制集的最佳实践，以充分利用MongoDB的这一强大特性。同时，遵循统一的编码标准，可以进一步提升开发效率和团队协作效果。

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www.AmbySoft.com/javaCodingStandards.pdf

1.5 Ambler’s Law of Standards

Whenever possible, reuse standards and guidelines, don’t reinvent them. The greater the scope of the

standards and guidelines the more desirable they are, industry standards are more desirable than

organizational standards which in turn are more desirable than project standards. Projects aren’t developed

in a vacuum and organizations do not operate in a vacuum either, therefore the greater the scope of the

standard the greater the chance that somebody else is also following it, making it that much easier for you to

work together with them.

Ambler’s Law of Standards

Industry standards > organizational standards > project standards >

personal standards > no standards

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www.AmbySoft.com/javaCodingStandards.pdf

2. Standards For Member Functions

I’m a firm believer in maximizing the productivity of systems professionals. Because I also recognize that an

application spends the majority of its existence being maintained, not developed, I am very interested in

anything that can help to make my code easier to maintain and to enhance, as well as to develop. Never

forget that the code that you write today may still be in use many years from now and will likely be

maintained and enhanced by somebody other than you. You must strive to make your code as “clean” and

understandable as possible, because these factors make it easier to maintain and to enhance.

In this section we will concentrate on four topics:

• Naming conventions

• Visibility

• Documentation conventions

• Techniques for writing clean Java code

2.1 Naming Member Functions

Member Functions should be named using a full English description, using mixed case with the first letter of

any non-initial word capitalized. It is also common practice for the first word of a member function name to

be a strong, active verb.

Examples:

openAccount()

printMailingLabel()

save()

delete()

This convention results in member functions whose purpose can often be determined just by looking at its

name. Although this convention results in a little extra typing by the developer, because it often results in

longer names, this is more than made up for by the increased understandability of your code.

2.1.1 Naming Accessor Member Functions

We will discuss accessors, member functions that get and set the values of fields (fields/properties) in

greater detail in chapter 3. The naming conventions for accessors, however, are summarized below.

2.1.1.1 Getters

Getters are member functions that return the value of a field. You should prefix the word ‘get’ to the name of

the field, unless it is a boolean field and then you prefix ‘is’ to the name of the field instead of ‘get.’

Examples:

getFirstName()

getAccountNumber()

getLostEh()

isPersistent()

isAtEnd()

www.AmbySoft.com/javaCodingStandards.pdf

By following this naming convention you make it obvious that a member function returns a field of an

object, and for boolean getters you make it obvious that it returns true or false. Another advantage of this

standard is that it follows the naming conventions used by the beans development kit (BDK) for getter

member functions (DeSoto, 1997). The main disadvantage is that ‘get’ is superfluous, requiring extra typing.

2.1.1.1.1 Alternative Naming Convention for Getters – Has and Can

A viable alternative, based on proper English conventions, is to use the prefix ‘has’ or ‘can’ instead of ‘is’

for boolean getters. For example, getter names such as hasDependents() and canPrint() make a lot of sense

when you are reading the code. The problem with this approach is that the BDK will not pick up on this

naming strategy (yet). You could rename these member functions isBurdenedWithDependents() and

isPrintable(). J

2.1.1.2 Setters

Setters, also known as mutators, are member functions that modify the values of a field. You should prefix

the word ‘set’ to the name of the field, regardless of the field type.

Examples:

setFirstName(String aName)

setAccountNumber(int anAccountNumber)

setReasonableGoals(Vector newGoals)

setPersistent(boolean isPersistent)

setAtEnd(boolean isAtEnd)

Following this naming convention you make it obvious that a member function sets the value of a field of an

object. Another advantage of this standard is that it follows the naming conventions used by the beans

development kit (BDK) for setter member functions (DeSoto, 1997). The main disadvantage is that ‘set’ is

superfluous, requiring extra typing.

2.1.1.3 Constructors

Constructors are member functions that perform any necessary initialization when an object is first created.

Constructors are always given the same name as their class. For example, a constructor for the class

Customer would be Customer(). Note that the same case is used.

Examples:

Customer()

SavingsAccount()

PersistenceBroker()

This naming convention is set by Sun and must be strictly adhered to.

www.AmbySoft.com/javaCodingStandards.pdf

2.2 Member Function Visibility

For a good design where you minimize the coupling between classes, the general rule of thumb is to be as

restrictive as possible when setting the visibility of a member function. If member function doesn’t have to

be public then make it protected, and if it doesn’t have to be protected then make it private.

Visibility Description Proper Usage

public A public member function can be invoked by

any other member function in any other

object or class.

When the member function must be

accessible by objects and classes outside of

the class hierarchy in which the member

function is defined.

protected A protected member function can be

invoked by any member function in the class

in which it is defined or any subclasses of

that class.

When the member function provides

behavior that is needed internally within the

class hierarchy but not externally.

private A private member function can only be

invoked by other member functions in the

class in which it is defined, but not in the

subclasses.

When the member function provides

behavior that is specific to the class. Private

member functions are often the result of

refactoring, also known as reorganizing, the

behavior of other member functions within

the class to encapsulate one specific

behavior.

No visibility is indicated. This is called

default or package visibility, and is

sometimes referred to as friendly visibility.

The member function is effectively public to

all other classes within the same package,

but private to classes external to the

package.

This is an interesting feature, but be careful

with its use. I use it when I’m building

domain components (Ambler, 1998b),

collections of classes that implement a

cohesive business concept such as

“Customer”, to restrict access to only the

classes within the component/package.

2.3 Documenting Member Functions

The manner in which you document a member function will often be the deciding factor as to whether or not

it is understandable, and therefore maintainable and extensible.

2.3.1 The Member Function Header

Every Java member function should include some sort of header, called member function documentation, at

the top of the source code that documents all of the information that is critical to understanding it. This

information includes, but is not limited to the following:

1. What and why the member function does what it does. By documenting what a member function does

you make it easier for others to determine if they can reuse your code. Documenting why it does

something makes it easier for others to put your code into context. You also make it easier for others to

determine whether or not a new change should actually be made to a piece of code (perhaps the reason

for the new change conflicts with the reason why the code was written in the first place).

2. What a member function must be passed as parameters. You also need to indicate what parameters, if

any, must be passed to a member function and how they will be used. This information is needed so

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