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Spring Dependencies and Depending on Spring

Although Spring provides integration and support for a huge range of enterprise and other external tools, it intentionally keeps its mandatory dependencies to an absolute minimum: you shouldn’t have to locate and download (even automatically) a large number of jar libraries in order to use Spring for simple use cases. For basic dependency injection there is only one mandatory external dependency, and that is for logging (see below for a more detailed description of logging options).

虽然Spring提供集成并支持大范围内的企业和其它外部工具，但它有意使它的强制性依赖到一个绝对最小化的程度：对于简单的用例你不应该为了使用Spring而定位和下载（即使是自动的）许多jar库。对于基本的依赖注入仅有一个强制性的外部依赖，那个依赖是关于日志的（在下面可以看到日志选择更详细的描述）。

Next we outline the basic steps needed to configure an application that depends on Spring, first with Maven and then with Gradle and finally using Ivy. In all cases, if anything is unclear, refer to the documentation of your dependency management system, or look at some sample code - Spring itself uses Gradle to manage dependencies when it is building, and our samples mostly use Gradle or Maven.

接下来我们概述配置一个依赖于Spring的应用需要的基本步骤，首先Maven的，其次是Gradle的，最后是Ivy的。在所有的案例中，如果有任何不清楚的地方，请参考你的依赖管理系统的文档，或者看一些示例代码——Spring本身构建时使用Gradle来管理依赖，我们例子中大多数是使用Gradle和Maven的。

Maven Dependency Management

If you are using Maven for dependency management you don’t even need to supply the logging dependency explicitly. For example, to create an application context and use dependency injection to configure an application, your Maven dependencies will look like this:

如果你正在使用Maven来进行依赖管理，那你不必显式的提供日志依赖。例如，为了创建一个应用上下文，使用依赖注入来配置一个应用，你的Maven依赖看上去是这样的：

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>5.0.0.BUILD-SNAPSHOT</version>
        <scope>runtime</scope>
    </dependency>
</dependencies>

That’s it. Note the scope can be declared as runtime if you don’t need to compile against Spring APIs, which is typically the case for basic dependency injection use cases.

就是它。注意如果你不需要编译Spring APIs，scope可以被声明成rumtime，这是典型的基本依赖注入的情况。

The example above works with the Maven Central repository. To use the Spring Maven repository (e.g. for milestones or developer snapshots), you need to specify the repository location in your Maven configuration. For full releases:

上面的例子是采用Maven中心仓库的。为了使用Spring Maven仓库(例如：使用milestone版本或snapshot版本)，你需要在Maven配置中指定仓库的位置，完整的版本：

<repositories>
    <repository>
        <id>io.spring.repo.maven.release</id>
        <url>http://repo.spring.io/release/</url>
        <snapshots><enabled>false</enabled></snapshots>
    </repository>
</repositories>

For milestones:
对于milestone版本：

<repositories>
    <repository>
        <id>io.spring.repo.maven.milestone</id>
        <url>http://repo.spring.io/milestone/</url>
        <snapshots><enabled>false</enabled></snapshots>
    </repository>
</repositories>

And for snapshots:
对于snapshot版本：

<repositories>   
    <repository>
        <id>io.spring.repo.maven.snapshot</id>
        <url>http://repo.spring.io/snapshot/</url>
        <snapshots><enabled>true</enabled></snapshots>
    </repository>
</repositories>

Maven "Bill Of Materials" Dependency

It is possible to accidentally mix different versions of Spring JARs when using Maven. For example, you may find that a third-party library, or another Spring project, pulls in a transitive dependency to an older release. If you forget to explicitly declare a direct dependency yourself, all sorts of unexpected issues can arise.

在使用Maven时，有可能会偶然的将不同版本的Spring JARs混合起来。例如，你可能找到一个第三方库，或另一个Spring项目，通过传递依赖进入了一个更旧的版本。如果你忘了自己显式的声明一个直接依赖，会产生各种意想不到的问题。

To overcome such problems Maven supports the concept of a "bill of materials" (BOM) dependency. You can import the spring-framework-bom in your dependencyManagement section to ensure that all spring dependencies (both direct and transitive) are at the same version.

为了解决这种问题，Maven支持"材料清单"(BOM)依赖的概念。你可以在你的dependencyManagement部分导入spring-framework-bom来确保所有的Spring依赖（直接和传递的）都是同一个版本。

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-framework-bom</artifactId>
            <version>5.0.0.BUILD-SNAPSHOT</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

An added benefit of using the BOM is that you no longer need to specify the <version> attribute when depending on Spring Framework artifacts:

使用BOM的额外好处是当依赖Spring框架的artifacts时你不再需要指定<version>属性：

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-web</artifactId>
    </dependency>
<dependencies>

Gradle Dependency Management

To use the Spring repository with the Gradle build system, include the appropriate URL in the repositories section:

为了在Gradle构建系统中使用Spring仓库，在repositories部分需要包含合适的URL：

repositories {
    mavenCentral()
    // and optionally...
    maven { url "http://repo.spring.io/release" }
}

You can change the repositories URL from /release to /milestone or /snapshot as appropriate. Once a repository has been configured, you can declare dependencies in the usual Gradle way:

当合适的时候你可以修改repositories的URL从/release到/milestone或/snapshot。一旦一个仓库被配置了，你可以用通常的Gradle方式声明依赖：

dependencies {
    compile("org.springframework:spring-context:5.0.0.BUILD-SNAPSHOT")
    testCompile("org.springframework:spring-test:5.0.0.BUILD-SNAPSHOT")
}

Ivy Dependency Management

If you prefer to use Ivy to manage dependencies then there are similar configuration options.

如果你更喜欢使用Ivy来管理依赖，这有类似的配置选择。

To configure Ivy to point to the Spring repository add the following resolver to your ivysettings.xml:

为了配置Ivy指定Spring仓库，添加下面的解析器到你的ivysettings.xml:

<resolvers>
    <ibiblio name="io.spring.repo.maven.release"
            m2compatible="true"
            root="http://repo.spring.io/release/"/>
</resolvers>

You can change the root URL from /release/ to /milestone/ or /snapshot/ as appropriate.

当合适的时候你可以更改根URL从repositories的URL从/release到/milestone或/snapshot。

Once configured, you can add dependencies in the usual way. For example (in ivy.xml):

一旦配置了，你可以通过一般的方式添加依赖。例如（在ivy.xml）:

<dependency org="org.springframework"
    name="spring-core" rev="5.0.0.BUILD-SNAPSHOT" conf="compile->runtime"/>

Distribution Zip Files

Although using a build system that supports dependency management is the recommended way to obtain the Spring Framework, it is still possible to download a distribution zip file.

尽管使用一个支持依赖管理的构建系统是获得Spring框架的推荐方式，但仍然可以下载发行版的Zip文件。

Distribution zips are published to the Spring Maven Repository (this is just for our convenience, you don’t need Maven or any other build system in order to download them).

发行版的zips是被发布到Spring Maven仓库（这只是为了我们的方便，为了下载它们你不需要Maven或任何其它的构建系统）。

To download a distribution zip open a web browser to http://repo.spring.io/release/org/springframework/spring and select the appropriate subfolder for the version that you want. Distribution files end -dist.zip, for example spring-framework-{spring-version}-RELEASE-dist.zip. Distributions are also published for milestones and snapshots.

为了下载发行版zip，打开浏览器输入http://repo.spring.io/release/org/springframework/spring，然后选择你想要的版本的合适子文件夹。发行版文件以-dist.zip结尾，例如spring-framework-{spring-version}-RELEASE-dist.zip。发行版也可以公布milestone版本或snapshots版本。

2.3.2 Logging

Logging is a very important dependency for Spring because a) it is the only mandatory external dependency, b) everyone likes to see some output from the tools they are using, and c) Spring integrates with lots of other tools all of which have also made a choice of logging dependency. One of the goals of an application developer is often to have unified logging configured in a central place for the whole application, including all external components. This is more difficult than it might have been since there are so many choices of logging framework.

日志对于Spring来说是一个非常重要的依赖，因为：a)它是唯一的强制性外部依赖，b)每个人都喜欢从他们使用的工具中看到一些输出，c)Spring集成了许多其它的工具，这些工具也选择了日志依赖。应用开发者的一个目标就是对于整个应用来讲，经常要有一个中心地方来进行日志的统一配置，包括所有的外部组件。比它更困难的可能是有太多的日志框架去选择。

The mandatory logging dependency in Spring is the Jakarta Commons Logging API (JCL). We compile against JCL and we also make JCL Log objects visible for classes that extend the Spring Framework. It’s important to users that all versions of Spring use the same logging library: migration is easy because backwards compatibility is preserved even with applications that extend Spring. The way we do this is to make one of the modules in Spring depend explicitly on commons-logging (the canonical implementation of JCL), and then make all the other modules depend on that at compile time. If you are using Maven for example, and wondering where you picked up the dependency on commons-logging, then it is from Spring and specifically from the central module called spring-core.

Spring中的强制日志依赖是Jakarta Commons Logging API (JCL)。我们编译JCL并使JCLlog对象对类是可见的，这扩展了Spring框架。所有版本的Spring采用同一个日志库：移植是容易的，因为即使应用扩展了Spring但保留了向后兼容性，这一点对用户来说很重要。我们实现这个的方式是让Spring的模块之一显式的依赖commons-logging(JCL的标准实现)，然后使其它模块在编译时依赖这个模块。例如如果你在使用Maven，想找出依赖于commons-logging的依赖在哪，它在Spring中，更确切的说它是在Spring的中心模块spring-core中。

The nice thing about commons-logging is that you don’t need anything else to make your application work. It has a runtime discovery algorithm that looks for other logging frameworks in well known places on the classpath and uses one that it thinks is appropriate (or you can tell it which one if you need to). If nothing else is available you get pretty nice looking logs just from the JDK (java.util.logging or JUL for short). You should find that your Spring application works and logs happily to the console out of the box in most situations, and that’s important.

关于commons-logging的一件好事是要使你的应用工作你不需要任何其它的东西。它有一个运行时发现算法，这个算法能寻找其它的日志框架在知名的classpath中，并使用一个它认为是合适的(或者你告诉它你想用哪个如果你需要的话)。如果找不到任何别的你可以从JDK中找到一个非常美好漂亮的日志(java.util.logging或缩写为JUL)。在大多数环境中你可以发现你的Spring应用恰当地运行并输出日志到控制台输出框中，那是很重要的。

Not Using Commons Logging

Unfortunately, the runtime discovery algorithm in commons-logging, while convenient for the end-user, is problematic. If we could turn back the clock and start Spring now as a new project it would use a different logging dependency. The first choice would probably be the Simple Logging Facade for Java ( SLF4J), which is also used by a lot of other tools that people use with Spring inside their applications.

不幸的是， 虽然commons-logging的运行时发现算法对于终端用户是方便的，但它是有问题的。如果我们将时钟回拨，把Spring作为一个新项目重新开始，将会选择一个不同的日志依赖。第一个选择可能是Simple Logging Facade for Java(SLF4J)，应用内部使用Spring的人使用的许多其它工具也用了SLF4J。

There are basically two ways to switch off commons-logging:

1. Exclude the dependency from the spring-core module (as it is the only module that explicitly depends on commons-logging)
2. Depend on a special commons-logging dependency that replaces the library with an empty jar (more details can be found in the SLF4J FAQ)

这儿有两种方式关掉commons-logging:

1. 从spring-core模块排除依赖（因为它是唯一的显式依赖）commons-logging的模块
2. 依赖于一个特定的commons-logging依赖，用一个空jar替换这个依赖（更多细节可以在SLF4J FAQ中找到）。

To exclude commons-logging, add the following to your dependencyManagement section:

为了排除commons-logging，把下面的内容加入到你的dependencyManagement部分：

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>5.0.0.BUILD-SNAPSHOT</version>
        <exclusions>
            <exclusion>
                <groupId>commons-logging</groupId>
                <artifactId>commons-logging</artifactId>
            </exclusion>
        </exclusions>
    </dependency>
</dependencies>

Now this application is probably broken because there is no implementation of the JCL API on the classpath, so to fix it a new one has to be provided. In the next section we show you how to provide an alternative implementation of JCL using SLF4J as an example.

现在这个应用可能是坏了的，因为在classpath中没有JCL API的实现，为了解决这个问题必须提供一个新的实现。在接下来的部分我们将向你展示怎样提供一个JCL替代实现，使用SLF4J就是一个例子。

Using SLF4J

SLF4J is a cleaner dependency and more efficient at runtime than commons-logging because it uses compile-time bindings instead of runtime discovery of the other logging frameworks it integrates. This also means that you have to be more explicit about what you want to happen at runtime, and declare it or configure it accordingly. SLF4J provides bindings to many common logging frameworks, so you can usually choose one that you already use, and bind to that for configuration and management.

SLF4J是一个更纯净的依赖并且在运行时比commons-logging更有效，因为它使用编译时绑定来代替运行时查找集成的其它日志框架。这也意味着你必须更清楚你想要运行时发生什么，然后相应的声明它或配置它。SLF4J提供跟许多常用日志框架的绑定，因此你通常可以选择一个你正在使用的日志框架，然后绑定到配置和管理上。

SLF4J provides bindings to many common logging frameworks, including JCL, and it also does the reverse: bridges between other logging frameworks and itself. So to use SLF4J with Spring you need to replace the commons-logging dependency with the SLF4J-JCL bridge. Once you have done that then logging calls from within Spring will be translated into logging calls to the SLF4J API, so if other libraries in your application use that API, then you have a single place to configure and manage logging.

SLF4J提供跟许多常用日志框架的绑定，包括JCL，它做的恰恰相反，建立其它日志框架和它自己的纽带。因此为了在Spring中使用SLF4J，你需要用SLF4J-JCL连接器取替换commons-logging依赖。一旦你在Spring内部使用了日志调用，Spring会将日志调用变为调用SLF4J API，如果你应用中其它的库调用了那个API，你将有一个单独的地方配置和管理日志。

A common choice might be to bridge Spring to SLF4J, and then provide explicit binding from SLF4J to Log4J. You need to supply 4 dependencies (and exclude the existing commons-logging): the bridge, the SLF4J API, the binding to Log4J, and the Log4J implementation itself. In Maven you would do that like this

一个常用的选择连接Spring和SLF4J，然后提供SLF4J到Log4J的显式绑定。你需要提供四个依赖(排除现有的commons-logging)：连接、SLF4J API、到Log4J的绑定、Log4J本身的实现。在Maven中你可能这么做：

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>5.0.0.BUILD-SNAPSHOT</version>
        <exclusions>
            <exclusion>
                <groupId>commons-logging</groupId>
                <artifactId>commons-logging</artifactId>
            </exclusion>
        </exclusions>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>jcl-over-slf4j</artifactId>
        <version>1.5.8</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>1.5.8</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-log4j12</artifactId>
        <version>1.5.8</version>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.14</version>
    </dependency>
</dependencies>

That might seem like a lot of dependencies just to get some logging. Well it is, but it is optional, and it should behave better than the vanilla commons-logging with respect to classloader issues, notably if you are in a strict container like an OSGi platform. Allegedly there is also a performance benefit because the bindings are at compile-time not runtime.

这可能看起来为了得到一些日志需要很多依赖。还好它是可选的，比起commons-logging的关于类加载器的问题，尤其是你在一个像OSGi平台那样严格的容器中的时候，它应该更好操作。据说这儿也有一个性能提升，因为绑定是在编译时而不是在运行时。

A more common choice amongst SLF4J users, which uses fewer steps and generates fewer dependencies, is to bind directly to Logback. This removes the extra binding step because Logback implements SLF4J directly, so you only need to depend on two libraries not four ( jcl-over-slf4j and logback). If you do that you might also need to exclude the slf4j-api dependency from other external dependencies (not Spring), because you only want one version of that API on the classpath.

在SLF4J用户中，一个更通用的选择是直接绑定到Logback，这样使用步骤更少且依赖也更少。这去除了外部绑定步骤，因为Logback直接实现了SLF4J，因此你仅需要依赖两个库而不是四个(jcl-over-slf4j和logback)。如果你这样做的话你可能也需要从其它的外部应用中（不是从Spring）排除slf4j-api依赖，因为你在classpath中仅需要一个版本的API。

Using Log4J

Many people use Log4j as a logging framework for configuration and management purposes. It’s efficient and well-established, and in fact it’s what we use at runtime when we build and test Spring. Spring also provides some utilities for configuring and initializing Log4j, so it has an optional compile-time dependency on Log4j in some modules.

许多人使用Log4j作为配置和管理的日志框架。它有效且完善的，当我们构建和测试Spring时，实际上这就是在运行时我们使用的东西。Spring也提供一些配置和初始化Log4j的工具，因此在某些模块有可选的Log4j的编译时依赖。

To make Log4j work with the default JCL dependency (commons-logging) all you need to do is put Log4j on the classpath, and provide it with a configuration file ( log4j.properties or log4j.xml in the root of the classpath). So for Maven users this is your dependency declaration:

为了使Log4j能与默认的JCL依赖(commons-logging)一起工作，所有你需要做的是把Log4j放到classpath中，并提供一个配置文件（log4j.properties或log4j.xml在classpath的根目录）。对于Maven用户依赖声明如下：

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>5.0.0.BUILD-SNAPSHOT</version>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.14</version>
    </dependency>
</dependencies>

And here’s a sample log4j.properties for logging to the console:

下面是一个log4j.properties输出日志到控制台的样本：

image

Runtime Containers with Native JCL

Many people run their Spring applications in a container that itself provides an implementation of JCL. IBM Websphere Application Server (WAS) is the archetype. This often causes problems, and unfortunately there is no silver bullet solution; simply excluding commons-logging from your application is not enough in most situations.

许多人在容器中运行他们的Spring应用，容器本身提供了一个JCL实现。IBM Websphere Application Server (WAS) 是原型。这经常会引起问题，不幸的是没有一劳永逸的解决方案；在大多数环境下简单的执行commons-logging是不够的。

To be clear about this: the problems reported are usually not with JCL per se, or even with commons-logging: rather they are to do with binding commons-logging to another framework (often Log4J). This can fail because commons-logging changed the way they do the runtime discovery in between the older versions (1.0) found in some containers and the modern versions that most people use now (1.1). Spring does not use any unusual parts of the JCL API, so nothing breaks there, but as soon as Spring or your application tries to do any logging you can find that the bindings to Log4J are not working.

为了使这个更清楚：报告的问题本质上一般不是关于JCL的，或关于commons-logging的：而是他们去绑定commons-logging到其它的框架上（通常是Log4j）。这可能会失败因为commons-logging在一些容器的旧版本（1.0）和大多数人使用的现代版本（1.1）中改变了运行时发现方式。Spring不使用JCL API的和任何不常用的部分，因此不会有问题出现，但是一旦Spring或你的应用试图去输出日志，你可能发现到Log4j的绑定是不起作用的。

In such cases with WAS the easiest thing to do is to invert the class loader hierarchy (IBM calls it "parent last") so that the application controls the JCL dependency, not the container. That option isn’t always open, but there are plenty of other suggestions in the public domain for alternative approaches, and your mileage may vary depending on the exact version and feature set of the container.

在这种情况下使用WAS最容易做的事是逆转类加载层（IBM称为"parent last"），为的是应用能控制依赖，而不是容器。虽然这种选择并非总是公开的，但在公共领域对于替代方法有许多其它的建议，你的解决这个问题花的时间可能是不同的，这取决于确定的版本和容器集合的特性。