Android建立网络连接，利用JSON数据获取百度图片搜索结果及GSON的简单使用

1、建立网络连接的基本方式

Android中建立网络连接最主要的方式是利用HttpURLConnection，示例如下：

public class HttpUtil {public static byte[] getUrlBytes(String urlSpec) throws IOException {//将地址信息封装成URLURL url = new URL(urlSpec);//创建指向URL链接的HttpURLConnection对象HttpURLConnection connection = (HttpURLConnection) url.openConnection();try {//保存返回结果ByteArrayOutputStream out = new ByteArrayOutputStream();//真正开始访问指定地址InputStream in = connection.getInputStream();//HTTP_OK才是成功建立链接if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {throw new IOException(connection.getResponseMessage() +": with " +urlSpec);}int bytesRead;byte[] buffer = new byte[1024];//不断从网络下载数据，并保存到out中while ((bytesRead = in.read(buffer)) > 0) {out.write(buffer, 0, bytesRead);}out.close();//下载完毕后，将结果转化成byte arrayreturn out.toByteArray();} finally {//断开连接connection.disconnect();}}public static String getUrlString(String urlSpec) throws IOException{//将byteArray转化为Stringreturn new String(getUrlBytes(urlSpec));}
}

2、下载百度图片对应的JSON数据

我们进入百度图片，例如“微距摄影”这个类别，其http地址如下：

http://image.baidu.com/search/index?tn=baiduimage&ipn=r&ct=201326592&cl=2&lm=-1&st=-1&sf=2&fmq=1480332039000_R_D&pv=&ic=0&nc=1&z=&se=&showtab=0&fb=0&width=&height=&face=0&istype=2&ie=utf-8&word=%E5%BE%AE%E8%B7%9D%E6%91%84%E5%BD%B1

其中：

http://image.baidu.com/search/index?

可以看作基础的http地址，后续的tn、ipn、ct等均是额外的访问参数。
例如：word后就是访问的类别，对应中文的“微距摄影”。

现在，基于这个地址，我们来看看如何获取百度图片搜索得到的结果：

public List<GalleryItem> fetchItems() {..............try {//解析基础地址String url = Uri.parse("http://image.baidu.com/search/index?").buildUpon()//增加参数，这里指定结果以json格式返回.appendQueryParameter("tn", "resultjson")//指定类别为微距摄影.appendQueryParameter("word", "微距摄影").build().toString();Log.d("ZJTest", url);String jsonString = HttpUtil.getUrlString(url);Log.d("ZJTest", jsonString);............} catch (JSONException | IOException e) {e.printStackTrace();}return items;
}

我们增加了log信息，看看生成的url：

02-14 09:59:49.154 32471-32506/stark.a.is.zhang.photogallery D/ZJTest: http://image.baidu.com/search/index?tn=resultjson&word=%E5%BE%AE%E8%B7%9D%E6%91%84%E5%BD%B1

可以看到，url的信息结构与前面的http地址相似。
这里我们只使用了tn、word参数，还可以按照同样的方式，增加其它的要求。

我们再看看返回的结果，为了方便观察，我们修改一下返回结果的格式，增加一些回车和空格：

02-14 09:59:49.354 32471-32506/stark.a.is.zhang.photogallery D/ZJTest:
{
"queryEnc":"%E5%BE%AE%E8%B7%9D%E6%91%84%E5%BD%B1",
"queryExt":"微距摄影",
"listNum":1965,
"displayNum":208527,
"gsm":"1000000001e",
"bdSearchTime":"",
"isNeedAsyncRequest":0,
"bdIsClustered":"1",
"data":[
{
"thumbURL":"http://f.hiphotos.baidu.com/image/h%3D300/sign=e444f9f5a0014c08063b2ea53a7a025b/359b033b5bb5c9ea18ae77bfdc39b6003af3b308.jpg",
"middleURL":"http://f.hiphotos.baidu.com/image/h%3D200/sign=1250a848b199a90124355c362d940a58/359b033b5bb5c9ea18ae77bfdc39b6003af3b308.jpg",    "largeTnImageUrl":"",
"hasLarge" :0,    "hoverURL":"http://f.hiphotos.baidu.com/image/h%3D300/sign=e444f9f5a0014c08063b2ea53a7a025b/359b033b5bb5c9ea18ae77bfdc39b6003af3b308.jpg",    "pageNum":0,
"objURL":"http://imgsrc.baidu.com/forum/pic/item/a8ec8a13632762d006deaa12a0ec08fa503dc6bf.jpg",    "fromURL":"http://tieba.baidu.com/p/1690102901",
"fromURLHost":"tieba.baidu.com",
"currentIndex":"",
"width":900,
"height":597,
"type":"jpg",
"filesize":"",
"bdSrcType":"-1",
"di":"0",
"adid":"0",
"is":"",
"simid_info":null,
"face_info":null,
"xiangshi_info":null,
"adPicId":"0",
"pi":"0",
"bdSetImgNum":0,
"bdImgnewsDate":"1970-01-01 08:00",
"fromPageTitle":"微距摄影",
"fromPageTitleEnc":"微距摄影",
"bdSourceName":"",
"bdFromPageTitlePrefix":"",
"token":""
},
{
"thumbURL":"http://img4.imgtn.bdimg.com/it/u=1193418232,3244632658&fm=23&gp=0.jpg",
"middleURL":"http://img4.imgtn.bdimg.com/it/u=1193418232,3244632658&fm=21&gp=0.jpg",
"largeTnImageUrl":"",
"hasLarge" :0,
"hoverURL":"http://img4.imgtn.bdimg.com/it/u=1193418232,3244632658&fm=23&gp=0.jpg",
"pageNum":1,
"objURL":"http://img4.duitang.com/uploads/item/201408/30/20140830185456_Eijik.jpeg",    "fromURL":"http://www.duitang.com/people/mblog/196468797/detail/",
"fromURLHost":"www.duitang.com",
"currentIndex":"",
"width":1200,
"height":800,
"type":"jpeg",
"filesize":"",
"bdSrcType":"0",
"di":"119581535480",
"adid":"0",
"is":"0,0",
"simid_info":null,
"face_info":null,
"xiangshi_info":null,
"adPicId":"0",
"pi":"0",
"bdSetImgNum":0,
"bdImgnewsDate":"1970-01-01 08:00",
"fromPageTitle":"<strong>微距摄影<\/strong>照片",
"fromPageTitleEnc":"微距摄影照片",
"bdSourceName":"",
"bdFromPageTitlePrefix":"",
"token":""
},
.........................

从上面的返回结果可以看出，JSON对象中的data域是一个数组，其中的每一项为实际的图片数据。
例如，我们可以获取data中的objURL，然后根据此地址获得实际的图片。

我们看看这部分完整的示例代码：

public class ImageFetcher {public List<GalleryItem> fetchItems() {//我们在GalleryItem中存储解析出的JSON数据List<GalleryItem> items = new ArrayList<>();try {String url = Uri.parse("http://image.baidu.com/search/index?").buildUpon().appendQueryParameter("tn", "resultjson").appendQueryParameter("word", "微距摄影").build().toString();String jsonString = HttpUtil.getUrlString(url);//将得到的返回结果分装到JSONObject中JSONObject jsonBody = new JSONObject(jsonString);//然后，解析JSONObjectparseItems(items, jsonBody);} catch (JSONException | IOException e) {e.printStackTrace();}return items;}private void parseItems(List<GalleryItem> items, JSONObject jsonBody)throws IOException, JSONException {//根据返回的JSON数据格式，我们知道“data”域对应JSONArrayJSONArray dataArray = jsonBody.getJSONArray("data");for (int i = 0; i < dataArray.length(); ++i) {JSONObject dataObject = dataArray.getJSONObject(i);GalleryItem item = new GalleryItem();//保存JSONArray中每一项的objURL，利用该Url就可以获取实际的数据item.setUrl(dataObject.getString("objURL"));items.add(item);}}
}

获取URL后的下载及解析图片的内容，在此篇博客中就不再进一步叙述了。

3、补充

上面获取JSON数据的方法实际上是不得已的“野路子”，如果百度图片修改了JSON结果的格式，那么代码也要随之修改。
一般正常情况下，应该使用云服务提供的API，然后按照API定义的JSON格式处理返回结果，例如使用Google、比应等提供的API接口。
不过为了使用云服务，必须申请对应的Api key，这就涉及到一些申请过程和收费了，具体的可以参考这些服务的说明文档。

使用云服务的好处在于：接口稳定，而且有一些便捷的方法可以使用，例如flickr提供的接口（这段代码的主要部分引用于Android权威指南）：

public void fetchItems() {try {String url = Uri.parse("https://api.flickr.com/services/rest/").buildUpon()//这就是云服务便利的地方，提供了方法给客户端使用.appendQueryParameter("method", "flickr.photos.getRecent")//这里需要填写申请到的api_key.appendQueryParameter("api_key", API_KEY).appendQueryParameter("format", "json")............build().toString();String jsonString = HttpUtil.getUrlString(url);//得到结果后，按照云服务约定的方式，解析JSON对象，方法与上面的代码类似....................} catch(IOException ioe) {............}
}

4、使用GSON来简化json数据的解析

对于固定格式的json数据而言，每次都用上述方式，分析数据格式然后逐步解析比较繁琐。
幸好有现成的第三方库Gson可以使用。

Gson的使用比较简单，主要是按照Json的格式定义序列化的Bean对象。

以上面百度图片返回的结果为例：

public class Response {//每个成员与Json中的key值一致private String queryEnc;private String queryExt;private String listNum;private String displayNum;private String gsm;private String bdSearchTime;private String isNeedAsyncRequest;private String bdIsClustered;//保存Json中的data数组private List<Data> data;public String getQueryEnc() {return queryEnc;}public void setQueryEnc(String queryEnc) {this.queryEnc = queryEnc;}public String getQueryExt() {return queryExt;}public void setQueryExt(String queryExt) {this.queryExt = queryExt;}public String getListNum() {return listNum;}public void setListNum(String listNum) {this.listNum = listNum;}public String getDisplayNum() {return displayNum;}public void setDisplayNum(String displayNum) {this.displayNum = displayNum;}public String getGsm() {return gsm;}public void setGsm(String gsm) {this.gsm = gsm;}public String getBdSearchTime() {return bdSearchTime;}public void setBdSearchTime(String bdSearchTime) {this.bdSearchTime = bdSearchTime;}public String getIsNeedAsyncRequest() {return isNeedAsyncRequest;}public void setIsNeedAsyncRequest(String isNeedAsyncRequest) {this.isNeedAsyncRequest = isNeedAsyncRequest;}public String getBdIsClustered() {return bdIsClustered;}public void setBdIsClustered(String bdIsClustered) {this.bdIsClustered = bdIsClustered;}public List<Data> getData() {return data;}public void setData(List<Data> data) {this.data = data;}
}

同样，再定义一个Data对象：

public class Data {//同样，Data中的成员与Json内data的key值一致private String thumbURL;private String middleURL;private String hasLarge;private String objURL;private String fromURLHost;private String currentIndex;private String width;private String height;private String type;private String filesize;private String bdSrcType;private String di;private String adid;private String is;private String simid_info;private String face_info;private String xiangshi_ifno;private String adPicId;private String pi;private String bdSetImgNum;private String bdImgnewsDate;private String fromPageTitle;private String fromPageTitleEnc;private String bdSourceName;private String bdFromPageTitlePrefix;private String token;public String getThumbURL() {return thumbURL;}public void setThumbURL(String thumbURL) {this.thumbURL = thumbURL;}public String getMiddleURL() {return middleURL;}public void setMiddleURL(String middleURL) {this.middleURL = middleURL;}public String getHasLarge() {return hasLarge;}public void setHasLarge(String hasLarge) {this.hasLarge = hasLarge;}public String getObjURL() {return objURL;}public void setObjURL(String objURL) {this.objURL = objURL;}public String getFromURLHost() {return fromURLHost;}public void setFromURLHost(String fromURLHost) {this.fromURLHost = fromURLHost;}public String getCurrentIndex() {return currentIndex;}public void setCurrentIndex(String currentIndex) {this.currentIndex = currentIndex;}public String getWidth() {return width;}public void setWidth(String width) {this.width = width;}public String getHeight() {return height;}public void setHeight(String height) {this.height = height;}public String getType() {return type;}public void setType(String type) {this.type = type;}public String getFilesize() {return filesize;}public void setFilesize(String filesize) {this.filesize = filesize;}public String getBdSrcType() {return bdSrcType;}public void setBdSrcType(String bdSrcType) {this.bdSrcType = bdSrcType;}public String getDi() {return di;}public void setDi(String di) {this.di = di;}public String getAdid() {return adid;}public void setAdid(String adid) {this.adid = adid;}public String getIs() {return is;}public void setIs(String is) {this.is = is;}public String getSimid_info() {return simid_info;}public void setSimid_info(String simid_info) {this.simid_info = simid_info;}public String getFace_info() {return face_info;}public void setFace_info(String face_info) {this.face_info = face_info;}public String getXiangshi_ifno() {return xiangshi_ifno;}public void setXiangshi_ifno(String xiangshi_ifno) {this.xiangshi_ifno = xiangshi_ifno;}public String getAdPicId() {return adPicId;}public void setAdPicId(String adPicId) {this.adPicId = adPicId;}public String getPi() {return pi;}public void setPi(String pi) {this.pi = pi;}public String getBdSetImgNum() {return bdSetImgNum;}public void setBdSetImgNum(String bdSetImgNum) {this.bdSetImgNum = bdSetImgNum;}public String getBdImgnewsDate() {return bdImgnewsDate;}public void setBdImgnewsDate(String bdImgnewsDate) {this.bdImgnewsDate = bdImgnewsDate;}public String getFromPageTitle() {return fromPageTitle;}public void setFromPageTitle(String fromPageTitle) {this.fromPageTitle = fromPageTitle;}public String getFromPageTitleEnc() {return fromPageTitleEnc;}public void setFromPageTitleEnc(String fromPageTitleEnc) {this.fromPageTitleEnc = fromPageTitleEnc;}public String getBdSourceName() {return bdSourceName;}public void setBdSourceName(String bdSourceName) {this.bdSourceName = bdSourceName;}public String getBdFromPageTitlePrefix() {return bdFromPageTitlePrefix;}public void setBdFromPageTitlePrefix(String bdFromPageTitlePrefix) {this.bdFromPageTitlePrefix = bdFromPageTitlePrefix;}public String getToken() {return token;}public void setToken(String token) {this.token = token;}
}

Bean对象定义完毕后，就可以使用Gson了，示例如下：

public class ImageFetcher {public List<GalleryItem> fetchItems() {List<GalleryItem> items = new ArrayList<>();try {String url = Uri.parse("http://image.baidu.com/search/index?").buildUpon().appendQueryParameter("tn", "resultjson").appendQueryParameter("word", "微距摄影").build().toString();String jsonString = HttpUtil.getUrlString(url);//创建GsonGson gson = new Gson();//Gson按照Response中的定义，将字符串解析成Response对象Response response = gson.fromJson(jsonString, Response.class);parseItems(items, response);} catch (JSONException | IOException e) {e.printStackTrace();}return items;}private void parseItems(List<GalleryItem> items, Response response)throws IOException, JSONException {//然后就可以直接调用对象的接口得到需要的数据了List<Data> dataList = response.getData();for (Data data : dataList) {GalleryItem item = new GalleryItem();item.setUrl(data.getObjURL());items.add(item);}}
}