このリファレンスガイドは、Spring Frameworkに関する詳細情報を提供します。Springが採用している基本的な概念（"依存性注入"など）に関するいくつかの背景に加えて、すべての機能に関する包括的なドキュメントを提供します。
Springを始めたばかりの場合は、 Spring Bootベースのアプリケーションを作成してSpring Frameworkの使用を開始することをお勧めします。Spring Bootは、プロダクション対応のSpringベースのアプリケーションを作成するための迅速な（そして定説のある）方法を提供します。 これはSpring Frameworkに基づいており、設定よりも規約を優先し、可能な限り迅速に起動して実行できるように設計されています。
start.spring.ioを使用して基本的なプロジェクトを生成するか、 ""始めよう" RESTful Webサービスの構築のような "始めよう"のガイドに従うことができます。 これらのガイドはダイジェストがより簡単であるだけでなく、非常にタスクに焦点を絞っており、それらのほとんどはSpring Bootに基づいています。 また、特定の問題を解決する際に検討が必要となる可能性がある、Springポートフォリオの他のプロジェクトもカバーしています。
The Spring Framework is a Java platform that provides comprehensive infrastructure support for developing Java applications. Spring handles the infrastructure so you can focus on your application.
Spring enables you to build applications from "plain old Java objects" (POJOs) and to apply enterprise services non-invasively to POJOs. This capability applies to the Java SE programming model and to full and partial Java EE.
Examples of how you, as an application developer, can benefit from the Spring platform:
-
Make a Java method execute in a database transaction without having to deal with transaction APIs.
-
Make a local Java method an HTTP endpoint without having to deal with the Servlet API.
-
Make a local Java method a message handler without having to deal with the JMS API.
-
Make a local Java method a management operation without having to deal with the JMX API.
A Java application — a loose term that runs the gamut from constrained, embedded applications to n-tier, server-side enterprise applications — typically consists of objects that collaborate to form the application proper. Thus the objects in an application have dependencies on each other.
Although the Java platform provides a wealth of application development functionality, it lacks the means to organize the basic building blocks into a coherent whole, leaving that task to architects and developers. Although you can use design patterns such as Factory, Abstract Factory, Builder, Decorator, and Service Locator to compose the various classes and object instances that make up an application, these patterns are simply that: best practices given a name, with a description of what the pattern does, where to apply it, the problems it addresses, and so forth. Patterns are formalized best practices that you must implement yourself in your application.
The Spring Framework Inversion of Control (IoC) component addresses this concern by providing a formalized means of composing disparate components into a fully working application ready for use. The Spring Framework codifies formalized design patterns as first-class objects that you can integrate into your own application(s). Numerous organizations and institutions use the Spring Framework in this manner to engineer robust, maintainable applications.
"The question is, what aspect of control are [they] inverting?" Martin Fowler posed this question about Inversion of Control (IoC) on his site in 2004. Fowler suggested renaming the principle to make it more self-explanatory and came up with Dependency Injection.
The Spring Framework consists of features organized into about 20 modules. These modules are grouped into Core Container, Data Access/Integration, Web, AOP (Aspect Oriented Programming), Instrumentation, Messaging, and Test, as shown in the following diagram.
The following sections list the available modules for each feature along with their artifact names and the topics they cover. Artifact names correlate to artifact IDs used in Dependency Management tools.
The Core Container consists of the spring-core,
spring-beans, spring-context, spring-context-support, and spring-expression
(Spring Expression Language) modules.
The spring-core and spring-beans modules provide the fundamental
parts of the framework, including the IoC and Dependency Injection features. The
BeanFactory is a sophisticated implementation of the factory pattern. It removes the
need for programmatic singletons and allows you to decouple the configuration and
specification of dependencies from your actual program logic.
The Context (spring-context) module builds on the solid
base provided by the Core and Beans modules: it is a means to
access objects in a framework-style manner that is similar to a JNDI registry. The
Context module inherits its features from the Beans module and adds support for
internationalization (using, for example, resource bundles), event propagation, resource
loading, and the transparent creation of contexts by, for example, a Servlet container.
The Context module also supports Java EE features such as EJB, JMX, and basic remoting.
The ApplicationContext interface is the focal point of the Context module.
spring-context-support provides support for integrating common third-party libraries
into a Spring application context for caching (EhCache, Guava, JCache), mailing
(JavaMail), scheduling (CommonJ, Quartz) and template engines (FreeMarker, JasperReports,
Velocity).
The spring-expression module provides a powerful Expression
Language for querying and manipulating an object graph at runtime. It is an extension
of the unified expression language (unified EL) as specified in the JSP 2.1
specification. The language supports setting and getting property values, property
assignment, method invocation, accessing the content of arrays, collections and indexers,
logical and arithmetic operators, named variables, and retrieval of objects by name from
Spring’s IoC container. It also supports list projection and selection as well as common
list aggregations.
The spring-aop module provides an AOP Alliance-compliant
aspect-oriented programming implementation allowing you to define, for example,
method interceptors and pointcuts to cleanly decouple code that implements functionality
that should be separated. Using source-level metadata functionality, you can also
incorporate behavioral information into your code, in a manner similar to that of .NET
attributes.
The separate spring-aspects module provides integration with AspectJ.
The spring-instrument module provides class instrumentation support and classloader
implementations to be used in certain application servers. The spring-instrument-tomcat
module contains Spring’s instrumentation agent for Tomcat.
Spring Framework 4 includes a spring-messaging module with key abstractions from the
Spring Integration project such as Message, MessageChannel, MessageHandler, and
others to serve as a foundation for messaging-based applications. The module also
includes a set of annotations for mapping messages to methods, similar to the Spring MVC
annotation based programming model.
The Data Access/Integration layer consists of the JDBC, ORM, OXM, JMS, and Transaction modules.
The spring-jdbc module provides a JDBC-abstraction layer that
removes the need to do tedious JDBC coding and parsing of database-vendor specific error
codes.
The spring-tx module supports programmatic and declarative transaction
management for classes that implement special interfaces and for all your POJOs (Plain
Old Java Objects).
The spring-orm module provides integration layers for popular
object-relational mapping APIs, including JPA,
JDO, and Hibernate. Using the spring-orm module you can
use all of these O/R-mapping frameworks in combination with all of the other features
Spring offers, such as the simple declarative transaction management feature mentioned
previously.
The spring-oxm module provides an abstraction layer that supports Object/XML
mapping implementations such as JAXB, Castor, XMLBeans, JiBX and XStream.
The spring-jms module (Java Messaging Service) contains features for producing and
consuming messages. Since Spring Framework 4.1, it provides integration with the
spring-messaging module.
The Web layer consists of the spring-web, spring-webmvc, spring-websocket, and
spring-webmvc-portlet modules.
The spring-web module provides basic web-oriented integration features such as
multipart file upload functionality and the initialization of the IoC container using
Servlet listeners and a web-oriented application context. It also contains an HTTP client
and the web-related parts of Spring’s remoting support.
The spring-webmvc module (also known as the Web-Servlet module) contains Spring’s
model-view-controller (MVC) and REST Web Services implementation
for web applications. Spring’s MVC framework provides a clean separation between domain
model code and web forms and integrates with all of the other features of the Spring
Framework.
The spring-webmvc-portlet module (also known as the Web-Portlet module) provides
the MVC implementation to be used in a Portlet environment and mirrors the functionality
of the Servlet-based spring-webmvc module.
The spring-test module supports the unit testing and
integration testing of Spring components with JUnit or TestNG. It
provides consistent loading of Spring
ApplicationContexts and caching of those
contexts. It also provides mock objects that you can use to test your
code in isolation.
The building blocks described previously make Spring a logical choice in many scenarios, from embedded applications that run on resource-constrained devices to full-fledged enterprise applications that use Spring’s transaction management functionality and web framework integration.
Spring’s declarative transaction management features make
the web application fully transactional, just as it would be if you used EJB
container-managed transactions. All your custom business logic can be implemented with
simple POJOs and managed by Spring’s IoC container. Additional services include support
for sending email and validation that is independent of the web layer, which lets you
choose where to execute validation rules. Spring’s ORM support is integrated with JPA,
Hibernate and JDO; for example, when using Hibernate, you can continue to use
your existing mapping files and standard Hibernate SessionFactory configuration. Form
controllers seamlessly integrate the web-layer with the domain model, removing the need
for ActionForms or other classes that transform HTTP parameters to values for your
domain model.
Sometimes circumstances do not allow you to completely switch to a different framework.
The Spring Framework does not force you to use everything within it; it is not an
all-or-nothing solution. Existing front-ends built with Struts, Tapestry, JSF
or other UI frameworks can be integrated with a Spring-based middle-tier, which allows
you to use Spring transaction features. You simply need to wire up your business logic
using an ApplicationContext and use a WebApplicationContext to integrate your web
layer.
When you need to access existing code through web services, you can use Spring’s
Hessian-, Burlap-, Rmi- or JaxRpcProxyFactory classes. Enabling remote access to
existing applications is not difficult.
The Spring Framework also provides an access and abstraction layer for Enterprise JavaBeans, enabling you to reuse your existing POJOs and wrap them in stateless session beans for use in scalable, fail-safe web applications that might need declarative security.
Dependency management and dependency injection are different things. To get those nice
features of Spring into your application (like dependency injection) you need to
assemble all the libraries needed (jar files) and get them onto your classpath at
runtime, and possibly at compile time. These dependencies are not virtual components
that are injected, but physical resources in a file system (typically). The process of
dependency management involves locating those resources, storing them and adding them to
classpaths. Dependencies can be direct (e.g. my application depends on Spring at
runtime), or indirect (e.g. my application depends on commons-dbcp which depends on
commons-pool). The indirect dependencies are also known as "transitive" and it is
those dependencies that are hardest to identify and manage.
If you are going to use Spring you need to get a copy of the jar libraries that comprise
the pieces of Spring that you need. To make this easier Spring is packaged as a set of
modules that separate the dependencies as much as possible, so for example if you don’t
want to write a web application you don’t need the spring-web modules. To refer to
Spring library modules in this guide we use a shorthand naming convention spring-* or
spring-*.jar, where * represents the short name for the module
(e.g. spring-core, spring-webmvc, spring-jms, etc.). The actual jar file name that
you use is normally the module name concatenated with the version number
(e.g. spring-core-{spring-version}.jar).
Each release of the Spring Framework will publish artifacts to the following places:
-
Maven Central, which is the default repository that Maven queries, and does not require any special configuration to use. Many of the common libraries that Spring depends on also are available from Maven Central and a large section of the Spring community uses Maven for dependency management, so this is convenient for them. The names of the jars here are in the form
spring-*-<version>.jarand the Maven groupId isorg.springframework. -
In a public Maven repository hosted specifically for Spring. In addition to the final GA releases, this repository also hosts development snapshots and milestones. The jar file names are in the same form as Maven Central, so this is a useful place to get development versions of Spring to use with other libraries deployed in Maven Central. This repository also contains a bundle distribution zip file that contains all Spring jars bundled together for easy download.
So the first thing you need to decide is how to manage your dependencies: we generally recommend the use of an automated system like Maven, Gradle or Ivy, but you can also do it manually by downloading all the jars yourself.
Below you will find the list of Spring artifacts. For a more complete description of each module, see Framework Modules.
| GroupId | ArtifactId | Description |
|---|---|---|
org.springframework |
spring-aop |
Proxy-based AOP support |
org.springframework |
spring-aspects |
AspectJ based aspects |
org.springframework |
spring-beans |
Beans support, including Groovy |
org.springframework |
spring-context |
Application context runtime, including scheduling and remoting abstractions |
org.springframework |
spring-context-support |
Support classes for integrating common third-party libraries into a Spring application context |
org.springframework |
spring-core |
Core utilities, used by many other Spring modules |
org.springframework |
spring-expression |
Spring Expression Language (SpEL) |
org.springframework |
spring-instrument |
Instrumentation agent for JVM bootstrapping |
org.springframework |
spring-instrument-tomcat |
Instrumentation agent for Tomcat |
org.springframework |
spring-jdbc |
JDBC support package, including DataSource setup and JDBC access support |
org.springframework |
spring-jms |
JMS support package, including helper classes to send/receive JMS messages |
org.springframework |
spring-messaging |
Support for messaging architectures and protocols |
org.springframework |
spring-orm |
Object/Relational Mapping, including JPA and Hibernate support |
org.springframework |
spring-oxm |
Object/XML Mapping |
org.springframework |
spring-test |
Support for unit testing and integration testing Spring components |
org.springframework |
spring-tx |
Transaction infrastructure, including DAO support and JCA integration |
org.springframework |
spring-web |
Foundational web support, including web client and web-based remoting |
org.springframework |
spring-webmvc |
HTTP-based Model-View-Controller and REST endpoints for Servlet stacks |
org.springframework |
spring-webmvc-portlet |
MVC implementation to be used in a Portlet environment |
org.springframework |
spring-websocket |
WebSocket and SockJS infrastructure, including STOMP messaging support |
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).
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.
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:
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>{spring-version}</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.
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:
<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:
<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:
<repositories>
<repository>
<id>io.spring.repo.maven.snapshot</id>
<url>http://repo.spring.io/snapshot/</url>
<snapshots><enabled>true</enabled></snapshots>
</repository>
</repositories>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.
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.
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-framework-bom</artifactId>
<version>{spring-version}</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:
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
</dependency>
<dependencies>To use the Spring repository with the Gradle build system,
include the appropriate URL in the repositories section:
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:
dependencies {
compile("org.springframework:spring-context:{spring-version}")
testCompile("org.springframework:spring-test:{spring-version}")
}If you prefer to use Ivy to manage dependencies then there are similar configuration options.
To configure Ivy to point to the Spring repository add the following resolver to your
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.
Once configured, you can add dependencies in the usual way. For example (in ivy.xml):
<dependency org="org.springframework"
name="spring-core" rev="{spring-version}" conf="compile->runtime"/>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.
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).
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.
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.
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.
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.
|
Note
|
Log4j 1.2 is EOL in the meantime. Also, Log4j 2.3 is the last Java 6 compatible release, with newer Log4j 2.x releases requiring Java 7+. |
Many people use Log4j as a logging framework for configuration and management purposes. It is efficient and well-established, and in fact it is what we use at runtime when we build Spring. Spring also provides some utilities for configuring and initializing Log4j, so it has an optional compile-time dependency on Log4j in some modules.
To make Log4j 1.2 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:
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>{spring-version}</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
</dependencies>And here’s a sample log4j.properties for logging to the console:
log4j.rootCategory=INFO, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %t %c{2}:%L - %m%n
log4j.category.org.springframework.beans.factory=DEBUG
To use Log4j 2.x with JCL, all you need to do is put Log4j on the classpath and
provide it with a configuration file (log4j2.xml, log4j2.properties, or other
supported configuration
formats). For Maven users, the minimal dependencies needed are:
<dependencies>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
<version>2.6.2</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-jcl</artifactId>
<version>2.6.2</version>
</dependency>
</dependencies>If you also wish to enable SLF4J to delegate to Log4j, e.g. for other libraries which use SLF4J by default, the following dependency is also needed:
<dependencies>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-slf4j-impl</artifactId>
<version>2.6.2</version>
</dependency>
</dependencies>Here is an example log4j2.xml for logging to the console:
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
<Appenders>
<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
</Console>
</Appenders>
<Loggers>
<Logger name="org.springframework.beans.factory" level="DEBUG"/>
<Root level="error">
<AppenderRef ref="Console"/>
</Root>
</Loggers>
</Configuration>Unfortunately, the runtime discovery algorithm in the standard commons-logging API,
while convenient for the end-user, can be problematic. If you’d like to avoid JCL’s
standard lookup, there are basically two ways to switch it off:
-
Exclude the dependency from the
spring-coremodule (as it is the only module that explicitly depends oncommons-logging) -
Depend on a special
commons-loggingdependency that replaces the library with an empty jar (more details can be found in the SLF4J FAQ)
To exclude commons-logging, add the following to your dependencyManagement section:
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>{spring-version}</version>
<exclusions>
<exclusion>
<groupId>commons-logging</groupId>
<artifactId>commons-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>Now this application is currently 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.
The Simple Logging Facade for Java (SLF4J) is a popular API used by other libraries commonly used with Spring. It is typically used with Logback which is a native implementation of the SLF4J API.
SLF4J provides bindings to many common logging frameworks, including Log4j, 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.
A common choice might be to bridge Spring to SLF4J, and then provide explicit binding
from SLF4J to Log4j. You need to supply several dependencies (and exclude the existing
commons-logging): the JCL bridge, the SLF4j binding to Log4j, and the Log4j provider
itself. In Maven you would do that like this
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>{spring-version}</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>1.7.21</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.21</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
</dependencies>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 just two libraries, namely jcl-over-slf4j and logback):
<dependencies>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>jcl-over-slf4j</artifactId>
<version>1.7.21</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.1.7</version>
</dependency>
</dependencies>Commons Logging will delegate to java.util.logging by default, provided that no
Log4j is detected on the classpath. So there is no special dependency to set up:
just use Spring with no external dependency for log output to java.util.logging,
either in a standalone application (with a custom or default JUL setup at the JDK
level) or with an application server’s log system (and its system-wide JUL setup).
Spring applications may run on a container that itself provides an implementation of JCL, e.g. IBM’s WebSphere Application Server (WAS). This does not cause issues per se but leads to two different scenarios that need to be understood:
In a "parent first" ClassLoader delegation model (the default on WAS), applications will always pick up the server-provided version of Commons Logging, delegating to the WAS logging subsystem (which is actually based on JUL). An application-provided variant of JCL, whether standard Commons Logging or the JCL-over-SLF4J bridge, will effectively be ignored, along with any locally included log provider.
With a "parent last" delegation model (the default in a regular Servlet container but an explicit configuration option on WAS), an application-provided Commons Logging variant will be picked up, enabling you to set up a locally included log provider, e.g. Log4j or Logback, within your application. In case of no local log provider, regular Commons Logging will delegate to JUL by default, effectively logging to WebSphere’s logging subsystem like in the "parent first" scenario.
All in all, we recommend deploying Spring applications in the "parent last" model since it naturally allows for local providers as well as the server’s log subsystem.