【Retrofit】简单介绍和使用

原文地址：

https://futurestud.io/blog/retrofit-getting-started-and-android-client#

Retrofit是什么

对于Retrofit ，官方的描述是：“A type-safe REST client for Android and Java.”它可以通过注解来描述Http请求，URL参数，查询参数，同时，它还支持多个请求体和文件上传。

引入到Android工程

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">dependencies {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Retrofit & OkHttp</span>
compile <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'com.squareup.retrofit2:retrofit:2.0.0-beta4'</span>
compile <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'com.squareup.retrofit2:converter-gson:2.0.0-beta4'</span>
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

对于后面的具体版本，一般使用官方最新的版本。 

Retrofit 2默认情况下利用okhttp为网络层，在它的基础上建立的。你不需要显式地定义okhttp作为你的项目的依赖性，除非你有一个特定的版本要求。

创建ServiceGenerator

首先是需要创建一个ServiceGenerator 类，它是使用整个框架的核心，它只有一个方法用来创建REST adapter

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> ServiceGenerator {

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> final String API_BASE_URL = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://your.api-base.url"</span>;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> OkHttpClient.Builder httpClient = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OkHttpClient.Builder();

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> Retrofit.Builder builder =
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Retrofit.Builder()
.baseUrl(API_BASE_URL)
.addConverterFactory(GsonConverterFactory.create());

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <S> S <span class="hljs-title" style="box-sizing: border-box;">createService</span>(Class<S> serviceClass) {
Retrofit retrofit = builder.client(httpClient.build()).build();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> retrofit.create(serviceClass);
}
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>

ServiceGenerator 类使用 Retrofit的restadapter Builder与给定的API库的URL创建一个新的REST客户端。例如，GitHub的API库的网址是https://api.github.com/。参数serviceclass是定义的API请求注释的类或接口。下面显示的具体用法的
Retrofit以及如何定义一个实例的客户端。

JSON映射

使用Retrofit 2时，需要明确的为Retrofit实例添加一个转化器，在上面的build.gradle文件中，为了引入GSON转化器，我们添加了下面这样一行：

<code class="hljs bash has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">compile <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'com.squareup.retrofit2:converter-gson:2.0.0-beta4'</span>  </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

现在，你可以在Retrofit’s builder上调用：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.addConverterFactory</span>(GsonConverterFactory<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.create</span>())</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

使GSON成为Retrofit内部默认的JSON转化器。

Retrofit 请求网络

下面是一个例子，客户端通过Retrofit 从github上面请求数据。首先新建一个GitHubClient 类，定义一个从github上获取一个开源库所有的贡献者的方法：

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">interface</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">GitHubClient</span> {</span>
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@GET</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"/repos/{owner}/{repo}/contributors"</span>)
Call<List<Contributor>> contributors(
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Path</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"owner"</span>) String owner,
<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Path</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"repo"</span>) String repo
);
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

{owner} 和 {repo} 在调用时会被替换成传入的参数，这个方法返回的是 

我们想要得到的Contributor集合

Contributor 实体类：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> Contributor {
String login;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> contributions;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

在上面添加JSON转化器后，Retrofit 会自动把请求的数据转化成实体类。

最后请求的代码：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> // Create a very simple REST adapter which points the GitHub API endpoint.
GitHubClient client = ServiceGenerator<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.createService</span>(GitHubClient<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

// Fetch <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">and</span> print a list of the contributors to this library.
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Call</span><List<Contributor>> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">call</span> =
client<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.contributors</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"fs_opensource"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"android-boilerplate"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

try {
List<Contributor> contributors = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">call</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.execute</span>()<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.body</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
} catch (IOException e) {
// handle errors
}

for (Contributor contributor : contributors) {
System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(
contributor<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.login</span> + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" ("</span> + contributor<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.contributions</span> + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">")"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul><div class="save_code tracking-ad" data-mod="popu_249" style="box-sizing: border-box; position: absolute; height: 60px; right: 30px; top: 5px; color: rgb(255, 255, 255); cursor: pointer; z-index: 2;"><a target=_blank style="color: rgb(255, 153, 0); box-sizing: border-box;"><img src="http://static.blog.csdn.net/images/save_snippets.png" style="border: none; box-sizing: border-box; max-width: 100%;" alt="" /></a></div>

首先通过ServiceGenerator 实例化 GitHubClient ，然后调用 GitHubClient 实例的contributors方法，得到Contributor集合，至此，一次完整的网络请求已经完成。

Demo地址：

http://download.csdn.net/detail/jiangxuqaz/9440960

转载：http://blog.csdn.net/jiangxuqaz/article/details/50708664