项目需求：

     jsonp是从前台js的角度考虑，通过Ajax调用springMVC的接口。同一个ip、同一个网络协议、同一个端口，三者都满足就是同一个域，否则就是跨域问题了。首页广告需要一个轮播的效果，取后台数据json格式。上篇博客介绍了使用jsonp来解决跨域，现在有个新的方法来解决，那就是：ajax请求地址改为自己系统的后台地址，之后在自己的后台用HttpClient请求url。封装好的跨域请求url工具类。封装一个get一个POST即可。

    两者的区别就在于，jsonp是基于客户端的跨域解决。而httpclient是基于服务端的跨域解决。

    我现在有两个maven项目：

Taotao-portal（8082端口）

Taotao-rest（8081端口）

    要使用httpclient需要在maven中引用（portal）：

<!-- httpclient -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
</dependency>

     
         
      
       org.apache.httpcomponents
          
      
       httpclient
      
     

    rest项目中写了个后台的服务调广告的数据，在portal项目中的service层来调用rest项目中的controller层提供的服务。

httpclient工作图解：

核心代码展示：

(portal项目)contentcontroller.java

@Controller
public class ContentController {
    @Autowired
    private ContentService contentService;

    //getdata
    @RequestMapping("/content/{cid}")
    @ResponseBody
    public TaotaoResult getConentList(@PathVariable Long cid){

        try {
            List<TbContent> list=contentService.getContentList(cid);
            return TaotaoResult.ok(list);
        } catch (Exception e) {
            e.printStackTrace();
            return TaotaoResult.build(500, ExceptionUtil.getStackTrace(e));
        }
    }
}

@Controllerpublic class ContentController {    @Autowired    private ContentService contentService;            //getdata    @RequestMapping("/content/{cid}")    @ResponseBody    public TaotaoResult getConentList(@PathVariable Long cid){                try {            List
     
       list=contentService.getContentList(cid);            return TaotaoResult.ok(list);        } catch (Exception e) {            e.printStackTrace();            return TaotaoResult.build(500, ExceptionUtil.getStackTrace(e));        }    }}
     

(portal项目)HttpClientUtil.java

package com.taotao.common.utils;

import java.io.IOException;
import java.net.URI;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URIBuilder;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

public class HttpClientUtil {

    public static String doGet(String url, Map<String, String> param) {

        // 创建Httpclient对象
        CloseableHttpClient httpclient = HttpClients.createDefault();

        String resultString = "";
        CloseableHttpResponse response = null;
        try {
            // 创建uri
            URIBuilder builder = new URIBuilder(url);
            if (param != null) {
                for (String key : param.keySet()) {
                    builder.addParameter(key, param.get(key));
                }
            }
            URI uri = builder.build();

            // 创建http GET请求
            HttpGet httpGet = new HttpGet(uri);

            // 执行请求
            response = httpclient.execute(httpGet);
            // 判断返回状态是否为200
            if (response.getStatusLine().getStatusCode() == 200) {
                resultString = EntityUtils.toString(response.getEntity(), "UTF-8");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (response != null) {
                    response.close();
                }
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return resultString;
    }

    public static String doGet(String url) {
        return doGet(url, null);
    }

    public static String doPost(String url, Map<String, String> param) {
        // 创建Httpclient对象
        CloseableHttpClient httpClient = HttpClients.createDefault();
        CloseableHttpResponse response = null;
        String resultString = "";
        try {
            // 创建Http Post请求
            HttpPost httpPost = new HttpPost(url);
            // 创建参数列表
            if (param != null) {
                List<NameValuePair> paramList = new ArrayList<>();
                for (String key : param.keySet()) {
                    paramList.add(new BasicNameValuePair(key, param.get(key)));
                }
                // 模拟表单
                UrlEncodedFormEntity entity = new UrlEncodedFormEntity(paramList);
                httpPost.setEntity(entity);
            }
            // 执行http请求
            response = httpClient.execute(httpPost);
            resultString = EntityUtils.toString(response.getEntity(), "utf-8");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                response.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

        return resultString;
    }

    public static String doPost(String url) {
        return doPost(url, null);
    }

    public static String doPostJson(String url, String json) {
        // 创建Httpclient对象
        CloseableHttpClient httpClient = HttpClients.createDefault();
        CloseableHttpResponse response = null;
        String resultString = "";
        try {
            // 创建Http Post请求
            HttpPost httpPost = new HttpPost(url);
            // 创建请求内容
            StringEntity entity = new StringEntity(json, ContentType.APPLICATION_JSON);
            httpPost.setEntity(entity);
            // 执行http请求
            response = httpClient.execute(httpPost);
            resultString = EntityUtils.toString(response.getEntity(), "utf-8");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                response.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

        return resultString;
    }
}

package com.taotao.common.utils;import java.io.IOException;import java.net.URI;import java.util.ArrayList;import java.util.List;import java.util.Map;import org.apache.http.NameValuePair;import org.apache.http.client.entity.UrlEncodedFormEntity;import org.apache.http.client.methods.CloseableHttpResponse;import org.apache.http.client.methods.HttpGet;import org.apache.http.client.methods.HttpPost;import org.apache.http.client.utils.URIBuilder;import org.apache.http.entity.ContentType;import org.apache.http.entity.StringEntity;import org.apache.http.impl.client.CloseableHttpClient;import org.apache.http.impl.client.HttpClients;import org.apache.http.message.BasicNameValuePair;import org.apache.http.util.EntityUtils;public class HttpClientUtil {    public static String doGet(String url, Map
     
       param) {        // 创建Httpclient对象        CloseableHttpClient httpclient = HttpClients.createDefault();        String resultString = "";        CloseableHttpResponse response = null;        try {            // 创建uri            URIBuilder builder = new URIBuilder(url);            if (param != null) {                for (String key : param.keySet()) {                    builder.addParameter(key, param.get(key));                }            }            URI uri = builder.build();            // 创建http GET请求            HttpGet httpGet = new HttpGet(uri);            // 执行请求            response = httpclient.execute(httpGet);            // 判断返回状态是否为200            if (response.getStatusLine().getStatusCode() == 200) {                resultString = EntityUtils.toString(response.getEntity(), "UTF-8");            }        } catch (Exception e) {            e.printStackTrace();        } finally {            try {                if (response != null) {                    response.close();                }                httpclient.close();            } catch (IOException e) {                e.printStackTrace();            }        }        return resultString;    }    public static String doGet(String url) {        return doGet(url, null);    }    public static String doPost(String url, Map
      
        param) {        // 创建Httpclient对象        CloseableHttpClient httpClient = HttpClients.createDefault();        CloseableHttpResponse response = null;        String resultString = "";        try {            // 创建Http Post请求            HttpPost httpPost = new HttpPost(url);            // 创建参数列表            if (param != null) {                List
       
         paramList = new ArrayList<>();                for (String key : param.keySet()) {                    paramList.add(new BasicNameValuePair(key, param.get(key)));                }                // 模拟表单                UrlEncodedFormEntity entity = new UrlEncodedFormEntity(paramList);                httpPost.setEntity(entity);            }            // 执行http请求            response = httpClient.execute(httpPost);            resultString = EntityUtils.toString(response.getEntity(), "utf-8");        } catch (Exception e) {            e.printStackTrace();        } finally {            try {                response.close();            } catch (IOException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }        return resultString;    }    public static String doPost(String url) {        return doPost(url, null);    }        public static String doPostJson(String url, String json) {        // 创建Httpclient对象        CloseableHttpClient httpClient = HttpClients.createDefault();        CloseableHttpResponse response = null;        String resultString = "";        try {            // 创建Http Post请求            HttpPost httpPost = new HttpPost(url);            // 创建请求内容            StringEntity entity = new StringEntity(json, ContentType.APPLICATION_JSON);            httpPost.setEntity(entity);            // 执行http请求            response = httpClient.execute(httpPost);            resultString = EntityUtils.toString(response.getEntity(), "utf-8");        } catch (Exception e) {            e.printStackTrace();        } finally {            try {                response.close();            } catch (IOException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }        return resultString;    }}
       
      
     

(rest项目)contentserviceimpl.java

@Service
public class ContentServiceImpl implements ContentService {

    //service 写活，读配置文件
    @Value("${REST_BASE_URL}")
    private String REST_BASE_URL;
    @Value("${REST_CONTENT_URL}")
    private String REST_CONTENT_URL;
    @Value("${REST_CONTENT_AD1_CID}")
    private String REST_CONTENT_AD1_CID;
    @Override
    public String getAd1List() {
        //调用服务获得数据  跨域请求：http://localhost:8081/content/89
        String json = HttpClientUtil.doGet(REST_BASE_URL + REST_CONTENT_URL + REST_CONTENT_AD1_CID);
        //把json转换成java对象
        TaotaoResult taotaoResult = TaotaoResult.formatToList(json, TbContent.class);
        //取data属性，内容列表
        List<TbContent> contentList = (List<TbContent>) taotaoResult.getData();
        //把内容列表转换成AdNode列表
        List<AdNode> resultList = new ArrayList<>();
        for (TbContent tbContent : contentList) {
            AdNode node = new AdNode();
            node.setHeight(240);
            node.setWidth(670);
            node.setSrc(tbContent.getPic());

            node.setHeightB(240);
            node.setWidthB(550);
            node.setSrcB(tbContent.getPic2());

            node.setAlt(tbContent.getSubTitle());
            node.setHref(tbContent.getUrl());

            resultList.add(node);
        }
        //需要把resultList转换成json数据
        String resultJson = JsonUtils.objectToJson(resultList);
        return resultJson;
    }
}

@Servicepublic class ContentServiceImpl implements ContentService {    //service 写活，读配置文件    @Value("${REST_BASE_URL}")    private String REST_BASE_URL;    @Value("${REST_CONTENT_URL}")    private String REST_CONTENT_URL;    @Value("${REST_CONTENT_AD1_CID}")    private String REST_CONTENT_AD1_CID;    @Override    public String getAd1List() {        //调用服务获得数据  跨域请求：http://localhost:8081/content/89        String json = HttpClientUtil.doGet(REST_BASE_URL + REST_CONTENT_URL + REST_CONTENT_AD1_CID);        //把json转换成java对象        TaotaoResult taotaoResult = TaotaoResult.formatToList(json, TbContent.class);        //取data属性，内容列表        List
     
       contentList = (List
      
       ) taotaoResult.getData();        //把内容列表转换成AdNode列表        List
       
         resultList = new ArrayList<>();        for (TbContent tbContent : contentList) {            AdNode node = new AdNode();            node.setHeight(240);            node.setWidth(670);            node.setSrc(tbContent.getPic());                        node.setHeightB(240);            node.setWidthB(550);            node.setSrcB(tbContent.getPic2());                        node.setAlt(tbContent.getSubTitle());            node.setHref(tbContent.getUrl());                        resultList.add(node);        }        //需要把resultList转换成json数据        String resultJson = JsonUtils.objectToJson(resultList);        return resultJson;    }}
       
      
     

(rest项目)indexcontroller

@Autowired
    private ContentService contentService;

    @RequestMapping("/index")
    public String showIndex(Model model){
        String json=contentService.getAd1List();
        model.addAttribute("ad1",json);
        return "index";
    }

@Autowired    private ContentService contentService;        @RequestMapping("/index")    public String showIndex(Model model){        String json=contentService.getAd1List();        model.addAttribute("ad1",json);        return "index";    }

查看网页源代码，可以看到传过来的json格式的数据。

总结：

      HttpClient与Jsonp能够轻易的解决跨域问题，从而得到自己想要的数据(来自不同IP，协议，端口)，唯一的不同点是，HttpClient是在Java代码中进行跨域访问，而Jsonp是在js中进行跨域访问。跨域还有一级跨域，二级跨域，更多内容值得研究。