Building-REST-Services-with-Spring资源-CSDN文库

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### 构建基于Spring的REST服务 #### 一、概览与基础知识在构建REST服务时，选择Spring作为开发框架是非常普遍的选择。Spring框架不仅功能强大且社区活跃，还提供了丰富的特性和工具来帮助开发者快速搭建高效的服务端应用。本文档将详细介绍如何使用Spring 3构建RESTful服务，并涵盖安全、发现性、错误处理等多个方面。 #### 二、构建基本的Web项目 1. **概述** 本章节主要介绍如何启动一个基本的Web应用项目，重点在于如何从传统的XML配置方式过渡到Java配置方式，无需完全抛弃原有的XML配置。 2. **Maven pom.xml配置详解** Maven是构建和管理Java项目的事实标准工具。以下是一个典型的`pom.xml`配置示例，用于创建一个基于Spring的Web应用： ```xml <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>org</groupId> <artifactId>rest</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>war</packaging> <dependencies>  <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>${spring.version}</version> </dependency>  <dependency> <groupId>org.springframework</groupId> <artifactId>spring-core</artifactId> <version>${spring.version}</version> </dependency>  <dependency> <groupId>ch.qos.logback</groupId> <artifactId>logback-classic</artifactId> <version>1.2.3</version> </dependency>  <dependency> <groupId>javax.servlet</groupId> <artifactId>javax.servlet-api</artifactId> <version>3.1.0</version> <scope>provided</scope> </dependency> </dependencies>  <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-war-plugin</artifactId> <version>3.2.2</version> <configuration> <failOnMissingWebXml>false</failOnMissingWebXml> </configuration> </plugin> </plugins> </build> </project> ``` 在上面的配置文件中，我们首先定义了项目的模型版本为4.0.0，接着设置了项目的基本信息（如`groupId`、`artifactId`和`version`），并指定了项目的打包类型为`war`，即Web应用归档文件。接下来是依赖管理部分，引入了Spring Web MVC和其他必要的依赖，如日志库Logback和Servlet API等。在`build`标签内配置了Maven War插件，确保项目能够正确打包为WAR文件。 #### 三、构建REST API 1. **Spring 3与Java配置** 一旦项目结构搭建完成，下一步就是使用Spring 3和Java配置来构建REST API。Spring 3支持通过Java配置类来替代XML配置文件，这种方式更加简洁且易于维护。开发者可以通过实现`WebMvcConfigurer`接口来自定义Spring MVC的功能，例如设置视图解析器、注册拦截器等。 2. **REST API设计原则** 在构建REST API之前，了解REST架构的基本原则非常重要。REST（Representational State Transfer）是一种软件架构风格，强调使用HTTP协议的资源定位能力。遵循REST原则可以帮助我们构建出易于理解和扩展的API。 #### 四、安全机制 1. **表单登录** 首先介绍了表单登录的安全机制，这是一种较为传统的登录方式，但可能不是最适用于RESTful API的设计模式。表单登录通常涉及到用户名和密码的提交，并通过服务器端验证后返回认证结果。 2. **基本认证（Basic Authentication）** 接下来介绍了基本认证（Basic Authentication），这是一种基于HTTP协议本身的认证机制。客户端在请求头中发送Base64编码后的用户名和密码，服务器通过验证这些信息来判断是否授权访问。 3. **摘要认证（Digest Authentication）** 摘要认证（Digest Authentication）则是一种更安全的认证方式，它通过哈希算法加密用户凭据，减少了密码在网络上传输的风险。 4. **基本认证与摘要认证的结合** 在实际应用中，可以将基本认证与摘要认证结合起来使用，提供更加灵活和安全的认证方案。 #### 五、REST API的发现性与HATEOAS 1. **REST API的发现性** 发现性是REST架构的一个重要特征，它指的是客户端能够通过服务器返回的信息发现更多的资源和服务。这一特性通过HATEOAS（Hypermedia as the Engine of Application State）原则得以体现，即超媒体作为应用程序状态的引擎。 2. **HATEOAS在Spring中的实现** 在Spring中实现HATEOAS可以通过多种方式来完成，比如使用Spring HATEOAS库来自动添加链接到响应体中，从而让客户端能够轻松地发现可用资源。 #### 六、ETags与版本控制 1. **ETags在Spring中的应用** ETags是一种HTTP头，用于标识某个资源的特定版本。Spring框架提供了内置的支持来处理ETags，这样可以在客户端缓存资源的同时，减少不必要的网络传输。 2. **REST API版本控制** 版本控制对于REST API来说至关重要，因为它允许开发者在不破坏现有客户端的情况下逐步改进服务。常见的版本控制策略包括使用URL路径、自定义头部或查询参数等方式来区分不同版本的API。 #### 七、错误处理 1. **Spring中的错误处理** 错误处理是REST API不可或缺的一部分。Spring提供了强大的异常处理机制，可以轻松地捕获和处理各种异常，并向客户端返回适当的HTTP状态码和错误信息。 #### 八、测试REST API 1. **多MIME类型的测试** 测试REST API时，确保能够正确处理不同的MIME类型是非常重要的。Spring Test框架提供了强大的工具来模拟HTTP请求，可以方便地测试API对不同数据格式的支持情况。通过以上几个方面的深入探讨，我们可以看到Spring不仅是一个强大的框架，而且非常适合用于构建高度可扩展、安全和易于维护的RESTful服务。无论是在项目初始化阶段还是后续的API设计与开发过程中，Spring都能提供全面的支持。

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REST with Spring ebook

Introduction

Over the course of this material, we’ll explore how to build a RESTful Service using Spring 3.

We’ll illustrate how to secure this service using various mechanisms – starting with the form-based login –

standard not necessarily well suited for REST, and moving to more RESTful solutions – Basic and Digest

Authentication.

Next, we’ll dig into Discoverability and the HATEOAS Constraint, and we’ll touch on more advanced subjects

such as implementing ETags functionality in Spring and error handling for a REST API.

Finally, we’ll discuss best practices for how to evolve and version a RESTful Service and we’ll end with a high

level look on how to test the API.

Table of Contents

I. Bootstrap the basic Web Project with Spring 3

II. Build the REST API with Spring 3 and Java Config

III. Security for REST – via Login Form

IV. Security for REST – via Basic Authentication

V. Security for REST – via Digest Authentication

VI. Security for REST – Basic and Digest Authentication together

VII. REST API Discoverability and HATEOAS

VIII. HATEOAS for a Spring REST Service

IX. ETags for REST with Spring

X. REST Pagination in Spring

XI. Error Handling for REST with Spring 3

XII. Versioning a REST API

XIII. Testing REST with multiple MIME types

REST with Spring ebook

2.1. Justification of the cglib dependency

You may wonder why cglib is a dependency – it turns out there is a valid reason to include it – the entire

configuration cannot function without it. If removed, Spring will throw:

Caused by: java.lang.IllegalStateException: CGLIB is required to process @Configuration classes. Either add

CGLIB to the classpath or remove the following @Configuration bean definitions

The reason this happens is explained by the way Spring deals with @Configuration classes. These classes are

effectively beans, and because of this they need to be aware of the Context, and respect scope and other bean

semantics. This is achieved by dynamically creating a cglib proxy with this awareness for each @Configuration

class, hence the cglib dependency.

Also, because of this, there are a few restrictions for Configuration annotated classes:

Configuration classes should not be final

They should have a constructor with no arguments

2.2. The cglib dependency in Spring 3.2

Starting with Spring 3.2, it is no longer necessary to add cglib as an explicit dependency. This is because

Spring is in now inlining cglib – which will ensure that all class based proxying functionality will work out of the

box with Spring 3.2.

The new cglib code is placed under the Spring package: org.springframework.cglib (replacing the original

net.sf.cglib). The reason for the package change is to avoid conflicts with any cglib versions already existing on

the classpath.

Also, the new cglib 3.0 is now used, upgraded from the older 2.2 dependency (see this JIRA issue for more

details).

3. The Java based web configuration

First, the @Configuration annotation – this is the main artifact used by the Java based Spring configuration; it is

itself meta-annotated with @Component, which makes the annotated classes standard beans and as such, also

candidates for component scanning. The main purpose of @Configuration classes is to be sources of bean

<cglib.version>2.2.2</cglib.version>

</properties>

</project>

@Configuration

@ImportResource( { "classpath*:/rest_config.xml" } )

@ComponentScan( basePackages = "org.rest" )

@PropertySource({ "classpath:rest.properties", "classpath:web.properties" })

public class AppConfig{

@Bean

public static PropertySourcesPlaceholderConfigurer properties() {

return new PropertySourcesPlaceholderConfigurer();

}

REST with Spring ebook

definitions for the Spring IoC Container. For a more detailed description, see the official docs.

Then, @ImportResource is used to import the existing XML based Spring configuration. This may be

configuration which is still being migrated from XML to Java, or simply legacy configuration that you wish to keep.

Either way, importing it into the Container is essential for a successful migration, allowing small steps without to

much risk. The equivalent XML annotation that is replaced is:

Moving on to @ComponentScan – this configures the component scanning directive, effectively replacing the

XML:

As of Spring 3.1, the @Configuration are excluded from classpath scanning by default – see this JIRA issue.

Before Spring 3.1 though, these classes should have been excluded explicitly:

The @Configuration classes should not be autodiscovered because they are already specified and used by the

Container – allowing them to be rediscovered and introduced into the Spring context will result in the following

error:

Caused by: org.springframework.context.annotation.ConflictingBeanDefinitionException: Annotation-specified

bean name ‘webConfig’ for bean class [org.rest.spring.AppConfig] conflicts with existing, non-compatible bean

definition of same name and class [org.rest.spring.AppConfig]

And finally, using the @Bean annotation to configure the properties support –

PropertySourcesPlaceholderConfigurer is initialized in a @Bean annotated method, indicating it will produce a

Spring bean managed by the Container. This new configuration has replaced the following XML:

For a more in depth discussion on why it was necessary to manually register the

PropertySourcesPlaceholderConfigurer bean, see the Properties with Spring Tutorial.

3.1. The web.xml

<context:component-scan base-package="org.rest" />

excludeFilters = { @ComponentScan.Filter( Configuration.class ) }

<context:property-placeholder

location="classpath:persistence.properties, classpath:web.properties"

ignore-unresolvable="true"/>

xml

version="1.0" encoding="UTF-8"?>

<web-app xmlns="

http://java.sun.com/xml/ns/javaee"

xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="

http://java.sun.com/xml/ns/javaee

http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"

id="rest" version="3.0">

<context-param>

<param-name>contextClass</param-name>

<param-value>

org.springframework.web.context.support.AnnotationConfigWebApplicationContext

REST with Spring ebook

Unlike XmlWebApplicationContext, it assumes no default configuration class locations, so the

“contextConfigLocation” init-param for the Servlet must be set. This will point to the java package where the

@Configuration classes are located; the fully qualified name(s) of the classes are also supported.

Next, the DispatcherServlet is configured to use the same kind of context, with the only difference that it’s loading

configuration classes out of a different package.

Other than this, the web.xml doesn’t really change from a XML to a Java based configuration.

4. Conclusion

The presented approach allows for a smooth migration of the Spring configuration from XML to Java, mixing

the old and the new. This is important for older projects, which may have a lot of XML based configuration that

cannot be migrated all at once. This way, the web.xml and bootstrapping of the application is the first step in a

migration, after which the remaining XML beans can be ported in small increments.

</param-value>

</context-param>

<context-param>

<param-name>contextConfigLocation</param-name>

<param-value>org.rest.spring.root</param-value>

</context-param>

<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>

</listener>

<servlet-name>rest</servlet-name>

<servlet-class>

org.springframework.web.servlet.DispatcherServlet

</servlet-class>

<init-param>

<param-name>contextClass</param-name>

<param-value>

org.springframework.web.context.support.AnnotationConfigWebApplicationContext

</param-value>

</init-param>

<init-param>

<param-name>contextConfigLocation</param-name>

<param-value>org.rest.spring.rest</param-value>

</init-param>

<load-on-startup>1</load-on-startup>

</servlet>

<servlet-mapping>

<servlet-name>rest</servlet-name>

<url-pattern>/api/*</url-pattern>

</servlet-mapping>

<welcome-file-list>

<welcome-file />

</welcome-file-list>

</web-app>

First, the root context is defined and configured to use AnnotationConfigWebApplicationContext instead of the

default XmlWebApplicationContext. The newer AnnotationConfigWebApplicationContext accepts @Configuration

annotated classes as input for the Container configuration and is needed in order to set up the Java based

context.

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