Retrofit入门[简单使用方式介绍哦]

其他 2018-12-18 13:28:49 阅读次数: 0
版权声明：本文为博主原创文章，如需转载请声明作者信息，谢谢。 https://blog.csdn.net/itCatface/article/details/78903304

一直用OkHttp感觉也没什么毛病，空闲时间看看Retrofit怎么使用
本篇仅介绍最基本的Retrofit用法，如有错误请提出，我会虚心请教并改正，谢谢

一、接口

想必有所了解的同学都知道Retrofit是基于接口来进行请求，如下

  1. 开门见山贴代码

    interface RetrofitApi {

    /* 1. 仅请求服务器数据 */
    @GET(".")
    fun register(): Call<String>


    /* 2. 上传参数 */
    @GET("hi/register")
    fun register(@QueryMap map: Map<String, String>): Call<String>


    /* 3. ???上传json[暂时处于僵硬状态...] */
    @POST("postJson")
    fun postJson(@Body user: User): Call<String>


    /* 4. 上传单个文件 */
    @Multipart
    @POST(".")
    fun uploadFile(@Part("description") description: RequestBody, @Part file: MultipartBody.Part): Call<String>


    /* 5. 上传多个文件 & 多个参数 */
    @JvmSuppressWildcards   // [IllegalArgumentException: Parameter type must not include a type variable or wildcard]
    @Multipart
    @POST(".")
    fun uploadFiles(@PartMap fileMap: Map<String, RequestBody>, @QueryMap map: Map<String, String>): Call<String>


    /* 6. 下载文件 */
    @Streaming  // 避免下载大文件被Retrofit整个读进内存
    @GET("downloadFile")
    fun download(): Call<ResponseBody>
}

    javabean数据类User如下

    data class User(val password: String, val username: String)

  2. 做个解释

    1. 上面的第三个上传json(或者有需求是上传xml的，这里没有成功实现，如有需要的同学联系我，然后我会尽快待补)

    2. 注意事项代码里都加注释了，再次说明几点

      • 有@Part的地方基本都要加@Multipart

      • 有@PartMap的地方最好加@JvmSuppressWildcards，否则会出错(注释有)

      • 下载文件时Retrofit会将文件流整个读进内存，避免OOM需添加@Streaming

二、具体的请求

刚开始，多写几遍最基本的请求步骤，加强记忆，不急着封装啥的

  1. 代码贴上

    object RetrofitRequest {

    @JvmStatic
    fun main(args: Array<String>) {
//        register()
//        registerWithParams()
//        postJson()
//        uploadFile()
//        uploadFiles()
        download()
    }


    private fun register() {
        // 先来个模子 -> 给模子加花 -> 通过模子刻个实例出来
        val retrofit = Retrofit.Builder()   // 创建客户端建造器
                .baseUrl("http://127.0.0.1:8080/hi/register/")   // 添加主机地址
                .addConverterFactory(ScalarsConverterFactory.create()) // 制定数据解析器[可用gson、jackson等或自定制]
                .build()    // 创建客户端实例

        val api = retrofit.create(RetrofitApi::class.java)  // 获取Api实例

        val call = api.register()   // 通过Api实例获取一个Call对象

        call.enqueue(object : Callback<String> {  // 开始请求[enqueue(异步) | execute(同步)]
            override fun onFailure(call: Call<String>?, t: Throwable?) {
                println("请求失败: ${t.toString()}")
            }

            override fun onResponse(call: Call<String>?, response: Response<String>?) {
                println("请求成功: ${response?.body()}")
            }
        })
    }


    private fun registerWithParams() {
        val retrofit = Retrofit.Builder()
                .baseUrl("http://127.0.0.1:8080/")
                .addConverterFactory(ScalarsConverterFactory.create())
                .build()

        val api = retrofit.create(RetrofitApi::class.java)

        val call = api.register(mapOf("username" to "catface", "password" to "root"))   // 添加请求参数map

        call.enqueue(object : Callback<String> {
            override fun onResponse(call: Call<String>?, response: Response<String>?) {
                println("请求成功: ${response?.body()}")
            }

            override fun onFailure(call: Call<String>?, t: Throwable?) {
                println("请求失败: ${t.toString()}")
            }

        })
    }


    // 僵硬中...
    private fun postJson() {
        val retrofit = Retrofit.Builder()
                .baseUrl("http://127.0.0.1:8080/")
                .addConverterFactory(GsonConverterFactory.create())
                .build()

        val api = retrofit.create(RetrofitApi::class.java)

        val call = api.postJson(User("root", "catface"))

        call.enqueue(object : Callback<String> {
            override fun onFailure(call: Call<String>?, t: Throwable?) {
                println("请求失败: ${t.toString()}")
            }

            override fun onResponse(call: Call<String>?, response: Response<String>?) {
                println("请求成功: ${response?.body()}")
            }
        })
    }


    private fun uploadFile() {
        val retrofit = Retrofit.Builder()
                .addConverterFactory(ScalarsConverterFactory.create())
                .baseUrl("http://127.0.0.1:8080/hi/uploadFileByJava/")
                .build()

        val api = retrofit.create(RetrofitApi::class.java)

        val file = File("D:/下载/图片/ic_launcher.png")
        val requestBody = RequestBody.create(MediaType.parse("multipart/form-data"), file)
        val fileBody = MultipartBody.Part.createFormData("file", file.name, requestBody)

        val description = RequestBody.create(MediaType.parse("multipart/form-data"), "This is a description")

        val call = api.uploadFile(description, fileBody)

        call.enqueue(object : Callback<String> {
            override fun onResponse(call: Call<String>, response: Response<String>) {
                println("请求成功: ${response.body().toString()}")
            }

            override fun onFailure(call: Call<String>, t: Throwable) {
                println("请求失败: ${t.toString()}")
            }
        })
    }


    private fun uploadFiles() {
        val retrofit = Retrofit.Builder()
                .baseUrl("http://127.0.0.1:8080/hi/uploadFileBySpringAndFileName/")
                .addConverterFactory(ScalarsConverterFactory.create())
                .build()

        val api = retrofit.create(RetrofitApi::class.java)

        /* 文件 */
        val fileMap = HashMap<String, RequestBody>()
        val file1 = File("D:/下载/图片/ic_launcher.png")
        val file2 = File("D:/下载/图片/girl01.jpg")
        fileMap.put("file1\"; filename=\"" + file1.name, RequestBody.create(MediaType.parse("multipart/form-data"), file1))
        fileMap.put("file2\"; filename=\"" + file2.name, RequestBody.create(MediaType.parse("multipart/form-data"), file2))

        /* 参数 */
        val map = HashMap<String, String>()
        map.put("username", "catface")
        map.put("password", "root")

        val call = api.uploadFiles(fileMap, map)

        call.enqueue(object : Callback<String> {
            override fun onResponse(call: Call<String>?, response: Response<String>?) {
                println("请求成功: ${response?.body()}")
            }

            override fun onFailure(call: Call<String>?, t: Throwable?) {
                println("请求失败: ${t.toString()}")
            }

        })
    }


    private fun download() {
        val retrofit = Retrofit.Builder()
                .baseUrl("http://127.0.0.1:8080/hi/")
                .addConverterFactory(ScalarsConverterFactory.create())
                .build()

        val api = retrofit.create(RetrofitApi::class.java)

        val call = api.download()

        call.enqueue(object : Callback<ResponseBody> {
            override fun onResponse(call: Call<ResponseBody>?, response: Response<ResponseBody>?) {
                println("请求成功")
                if (response!!.isSuccessful) {
                    writeResponseBodyToDisk(response.body()!!)
                }
            }

            override fun onFailure(call: Call<ResponseBody>?, t: Throwable?) {
                println("请求失败: ${t.toString()}")
            }

        })
    }


    /* 将流写到本地的工具 */
    fun writeResponseBodyToDisk(body: ResponseBody): Boolean {
        try {
            val futureStudioIconFile = File("d:/a_test_dir/Future Studio Icon.jpg")

            var inputStream: InputStream? = null
            var outputStream: OutputStream? = null

            try {
                val fileReader = ByteArray(4096)

                val fileSize = body.contentLength()
                var fileSizeDownloaded: Long = 0

                inputStream = body.byteStream()
                outputStream = FileOutputStream(futureStudioIconFile)

                while (true) {
                    val read = inputStream!!.read(fileReader)

                    if (read == -1) {
                        break
                    }

                    outputStream.write(fileReader, 0, read)

                    fileSizeDownloaded += read.toLong()

                    println("file download: $fileSizeDownloaded of $fileSize")
                }

                outputStream.flush()

                return true
            } catch (e: IOException) {
                return false
            } finally {
                if (inputStream != null) {
                    inputStream.close()
                }

                if (outputStream != null) {
                    outputStream.close()
                }
            }
        } catch (e: IOException) {
            return false
        }
    }
}

  2. 做个解释

    1. 在数据解析器方面，我觉得直接返回json串后自己使用gson或者fastjson解析，又清楚也不麻烦，不太喜欢在构造Retrofit实例的时候就固定了解析方式，当然如果为了方便项目需求需要加也没问题

    2. 步骤大致就是：创建Retrofit实例，然后通过接口定义的请求得到Api实例，通过这个实例得到对应的Call对象，最后进行具体的请求

三、服务端

为了方便同学们了解服务端是怎么接收文件和参数的，在此贴出我写的完整的服务端小demo，可做大家入门案例，灰常简单，且功能很全，能接收客户端传来的各种参数、文件，而且能返回给客户端字符串、json串、还能提供文件给客户端进行下载，直接看，不用害怕

  1. Controller代码贴上

    @Controller
@RequestMapping("hi")
public class HiController {

    /******************************************** 与客户端进行入参出参联系 ********************************************/
    /**
     * 1. 接收参数 --> 返回字符串
     */
    @RequestMapping(value = "/register", produces = "application/json; charset=utf-8")
    @ResponseBody
    public String register(HttpServletRequest request) {
        System.out.println("接口开始执行-->register");

        Map<String, String[]> map = request.getParameterMap();

        if (null == map || map.size() < 1) return "本次请求未上传任何参数";

        String result = "";
        for (String key : map.keySet()) {
            System.out.println(key + "-" + map.get(key)[0]);

            result += "\r\n" + key + "-" + map.get(key)[0];
        }

        return result;
    }


    /**
     * 接收json串
     */
    @RequestMapping(value = "/postJson", method = RequestMethod.POST, produces = "application/json; charset=utf-8")
    @ResponseBody
    public String postJson(@RequestBody Map<String, String> map) throws IOException {
        System.out.println("接口开始执行-->postJson");

        if (null == map || map.size() < 1) return "本次请求未上传任何参数";

        String result = "";
        for (String key : map.keySet()) {
            System.out.println(key + "-" + map.get(key));

            result += "\r\n" + key + "-" + map.get(key);
        }

        return result;
    }

    /**
     * 2. 接收参数 --> 返回json
     */
    @RequestMapping(value = "/login", produces = "application/json; charset=utf-8")
    @ResponseBody
    public String login(@RequestParam("username") String username, @RequestParam("password") String password) throws IOException {
        System.out.println("接口开始执行-->login");

        /* 接收入参 */
        System.out.println(username + " || " + password);


        /* 提供出参[json格式] */
        Map<String, String> map = new HashMap<String, String>();
        map.put("username", "测试中文 your username is: " + username);
        map.put("password", "测试中文 your password is: " + password);

        /* 返回json给客户端 */
        return JSON.toJSONString(map);
    }


    @RequestMapping(value = "/receiveArr")
    public void receiveArr(@RequestParam("ids[]") String[] ids) {
        System.out.println("接口开始执行-->receiveArr");

        for (String id : ids) {
            System.out.println(id);
        }
    }

    /******************************************** 客户端上传文件 ********************************************/
    /**
     * ↓通过流保存上传的文件(耗时较长)
     *
     * @param file 将文件封装成CommonsMultipartFile
     */
    @RequestMapping("/uploadFileByStream")
    @ResponseBody
    public String uploadFileByStream(@RequestParam("file") CommonsMultipartFile file) throws IOException {
        System.out.println("接口开始执行-->uploadFileByStream");

        OutputStream os = new FileOutputStream("d:/" + file.getOriginalFilename());

        InputStream is = file.getInputStream();

        int temp;
        while ((temp = is.read()) != -1) {
            os.write(temp);
        }

        os.flush();
        os.close();
        is.close();

        return "uploadFileByStream suc...";
    }


    /**
     * ↓通过Java API: file.transferTo()保存上传的单个文件
     */
    @RequestMapping("/uploadFileByJava")
    @ResponseBody
    public String uploadFileByJava(@RequestParam("file") CommonsMultipartFile file) throws IOException {
        System.out.println("接口开始执行-->uploadFileByJava");

        file.transferTo(new File("d:/" + file.getOriginalFilename()));

        return "uploadFileByJava suc... ";
    }


    /**
     * ↓通过Spring API保存上传的多个文件
     */
    @RequestMapping("/uploadFilesBySpring")
    @ResponseBody
    public String uploadFilesBySpring(HttpServletRequest request) throws IOException {
        System.out.println("接口开始执行-->uploadFilesBySpring");

        String desPath;

        CommonsMultipartResolver multipartResolver = new CommonsMultipartResolver(request.getSession().getServletContext());
        if (multipartResolver.isMultipart(request)) {
            MultipartHttpServletRequest multiRequest = (MultipartHttpServletRequest) request;

            Iterator<String> iterator = multiRequest.getFileNames();

            while (iterator.hasNext()) {
                MultipartFile file = multiRequest.getFile(iterator.next());

                if (null != file) {
                    desPath = "d:/tt/" + file.getOriginalFilename();
                    file.transferTo(new File(desPath));
                }
            }
        }

        return "uploadFilesBySpring suc...";
    }


    /**
     * →接收文件map & 请求参数map←
     */
    @RequestMapping(value = "/uploadFileBySpringAndFileName", method = RequestMethod.POST, produces = "application/json; charset=utf-8")
    @ResponseBody
    public String uploadFileBySpringAndFileName(HttpServletRequest request) throws IOException {
        System.out.println("接口开始执行-->uploadFileBySpringAndFileName");

        /* 1. 获取所有参数 */
        Map<String, String[]> parameterMap = request.getParameterMap();

        System.out.println("参数数量: " + parameterMap.size()); // 入参数量

        for (String key : parameterMap.keySet()) {
            System.out.println(key + ":" + parameterMap.get(key)[0]);
        }

         /* 2. 获取所有文件 */
        CommonsMultipartResolver multiResolver = new CommonsMultipartResolver(request.getSession().getServletContext());

        if (multiResolver.isMultipart(request)) {
            MultipartHttpServletRequest multiRequest = (MultipartHttpServletRequest) request;

            MultiValueMap<String, MultipartFile> multiFileMap = multiRequest.getMultiFileMap();
            System.out.println("文件数量: " + multiFileMap.size()); // 入参数量
            for (String key : multiFileMap.keySet()) {
                System.out.println(key + " : " + multiFileMap.get(key).get(0).getOriginalFilename());
                multiFileMap.get(key).get(0).transferTo(new File("d:/a_test_dir/" + multiFileMap.get(key).get(0).getOriginalFilename()));
            }


            /*Iterator<String> iterator = multiRequest.getFileNames();

            while (iterator.hasNext()) {
                Map<String, MultipartFile> fileMap = multiRequest.getFileMap();

                MultipartFile file = fileMap.get("file");

                System.out.println(file.getOriginalFilename());
            }*/
        }

        return "uploadFileBySpringAndFileName suc...";
    }


    /* 添加一个网上的小demo，没啥用，随便看看 */
    @RequestMapping("/uploadFiles")
    @ResponseBody
    public String uploadFiles(HttpServletRequest request) throws IOException {
        System.out.println("接口开始执行-->uploadFiles");

        //创建一个通用的多部分解析器
        CommonsMultipartResolver multipartResolver = new CommonsMultipartResolver(request.getSession().getServletContext());
        //判断 request 是否有文件上传,即多部分请求
        if (multipartResolver.isMultipart(request)) {
            //转换成多部分request
            MultipartHttpServletRequest multiRequest = (MultipartHttpServletRequest) request;
            //取得request中的所有文件名
            Iterator<String> iter = multiRequest.getFileNames();
            while (iter.hasNext()) {
                //记录上传过程起始时的时间，用来计算上传时间
                int pre = (int) System.currentTimeMillis();
                //取得上传文件
                MultipartFile file = multiRequest.getFile(iter.next());
                if (file != null) {
                    //取得当前上传文件的文件名称
                    String myFileName = file.getOriginalFilename();
                    //如果名称不"",说明该文件存在，否则说明该文件不存在
                    if (myFileName.trim() != "") {
                        System.out.println(myFileName);
                        //重命名上传后的文件名
                        String fileName = "demoUpload" + file.getOriginalFilename();
                        //定义上传路径
                        String path = "D:/a_test_dir/" + fileName;
                        File localFile = new File(path);
                        file.transferTo(localFile);
                    }
                }
                //记录上传该文件后的时间
                int finaltime = (int) System.currentTimeMillis();
                System.out.println(finaltime - pre);
            }
        }

        return "/success";
    }

    /******************************************* 向页面输出验证码png ********************************************/
    @RequestMapping("/verificationCode")
    public void verificationCode(HttpServletResponse response, HttpSession session) throws IOException {
        System.out.println("接口开始执行-->verificationCode");

        Object[] objs = ImageUtil.createImage();
        session.setAttribute("imgCode", objs[0]);

        BufferedImage img = (BufferedImage) objs[1];
        response.setContentType("image/png");
        OutputStream os = response.getOutputStream();
        ImageIO.write(img, "png", os);
    }


    /******************************************* 向客户端提供文件下载 ********************************************/
    @RequestMapping("/downloadFile")
    public ResponseEntity<byte[]> downloadFile() throws IOException {
        System.out.println("接口开始执行-->downloadFile");

        File file = new File("C:\\Users\\Administrator\\Desktop\\temp.jpg");

        HttpHeaders headers = new HttpHeaders();
        headers.setContentDispositionFormData("attachment", "temp.jpg");
        headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
        headers.setContentLength(file.length());

        System.out.println(file.length() + " is length,..");

        return new ResponseEntity<byte[]>(FileUtils.readFileToByteArray(file), headers, HttpStatus.CREATED);
    }
}

  2. 做个解释

    1. 服务器就基于SSM(SpringMVC+Spring+Mybatis)

    2. 新手学习中，本篇未涉及难点和概念部分，即看完能够在项目中使用

    3. 如有关于Retrofit和服务端的问题，请留下回复，一起交流

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