No 'Access-Control-Allow-Origin' header is present on the requested resource.'Ajax跨域访问解决，前后端分离存在的问题

今天页面联调时出现了No 'Access-Control-Allow-Origin这样的问题，这个问题 当然有经验的老司机肯定可以看出来是跨域问题，这里对于这样的问题做一次总结。面试可能会被问到，前后分离存在什么问题，你可以回答说跨域的问题，如果你答上来了，可能会问你下一个问题，怎么解决？下面是我个人总结的。

解决方案1 jsonp

这种技术是在ajax里面进行声明，客户端的解决方案。

具体实现如下：

$(function($){
var url = 'http://xxxxxxx/index';
$.ajax(url, {
data: {
'cityname': '',
'date': '2016.12.12'
},
dataType: 'jsonp',
crossDomain: true,
success: function(data) {
if(data && data.resultcode == '200'){
console.log(data.result.today);
}
}
});

将ajax请求中的dataType属性设置为“jsonp”。

2.后台处理 spring针对跨域提供了注解 @CrossOrigin

1>Spring 4.2之后提供了跨域注解 @CrossOrigin;

2>可以用在方法或Controller上;

实现方式如下：

package com.arror.code_factory.controller;
import com.arror.code_factory.dao.DataBaseDAO;
import com.arror.code_factory.handler.GenerateTableSqlHandler;
import com.arror.code_factory.parm.SQLParam;
import org.springframework.web.bind.annotation.*;

import javax.annotation.Resource;
import java.util.List;

/**
 * @Description
 * @Author DJZ-WWS
 * @Date 2019/5/30 11:26
 */
@RestController
@CrossOrigin
public class SQLController {
    @Resource
    private GenerateTableSqlHandler handler;
    @Resource
    private DataBaseDAO dataBaseDao;

    @PostMapping("/createDaoPojoServiceImpl")
    public String createDaoPojoServiceImpl(@RequestBody List sqlParam) {
        //触发生成pojo
        handler.handler(sqlParam);
        return "ok";
    }
    @GetMapping("getDataBaseTables/{dataBaseName}")
    public   List  getDataBaseTables(@PathVariable String dataBaseName){
        //获取指定数据库的所有表信息
        List tableList = dataBaseDao.listTables(dataBaseName);
        return   tableList;
    }
}

3、使用Filter过滤处理器

一般的处理方法，在Filter中拦截请求，在请求头中添加信息，例如：

setHeader("Access-Control-Allow-Origin","*")

 

 

4.使用Nginx配置处理跨域（这种方式暂时没有做研究）

5.使用springmvc拦截器

在我们的实际项目使用是spring的注解还有就是Filter过滤器

代码如下：

public class CorsFilter implements Filter {

private String[] m_allowedOrigins = {"*"};
private String m_allowedMethods = "GET,POST,HEAD,OPTIONS,PUT,DELETE";
private List m_lstAllowedMethods = null;
private String m_allowedHeaders = "Content-Type,X-Requested-With,accept,Origin,Access-Control-Request-Method,Access-Control-Request-Headers";
private List m_lstAllowedHeaders = null;
private boolean m_supportCredentials = true;
private String m_preflightMaxAge = "1000";

@Override
public void init(FilterConfig config) throws ServletException {
String sAllowedOrigins = config.getInitParameter("cors.allowed.origins");
String sAllowedMethods = config.getInitParameter("cors.allowed.methods");
String sAllowedHeaders = config.getInitParameter("cors.allowed.headers");
String sSupportCredentials = config.getInitParameter("cors.support.credentials");
String sPreflightMaxAge = config.getInitParameter("cors.preflight.maxage");
if (sAllowedOrigins != null) {
m_allowedOrigins = sAllowedOrigins.toLowerCase().split("\\s*,\\s*");
}
if (sAllowedMethods != null) {
m_allowedMethods = sAllowedMethods;
m_lstAllowedMethods = Arrays.asList(m_allowedMethods.toLowerCase().split("\\s*,\\s*"));
}
if (sAllowedHeaders != null) {
m_allowedHeaders = sAllowedHeaders;
m_lstAllowedHeaders = Arrays.asList(m_allowedHeaders.toLowerCase().split("\\s*,\\s*"));
}
if (sSupportCredentials != null) {
m_supportCredentials = sSupportCredentials.equals("true");
}
if (sPreflightMaxAge != null) {
m_preflightMaxAge = sPreflightMaxAge;
}
}

@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse res = (HttpServletResponse) response;
String origin = req.getHeader("Origin");
if (origin != null) {
boolean matchFound = false;
for (String s : m_allowedOrigins) {
if (match(origin, s)) {
matchFound = true;
break;
}
}
if (!matchFound) {
chain.doFilter(req, res);
return;
}
if (req.getMethod() != null && req.getMethod().equals("OPTIONS")) {
String method = req.getHeader("Access-Control-Request-Method");
String strHeaders = req.getHeader("Access-Control-Request-Headers");

if (method == null) {
chain.doFilter(req, res);
return;
}
List headers = strHeaders == null ? new ArrayList() : Arrays.asList(strHeaders.split("\\s*,\\s*"));
if (!m_lstAllowedMethods.contains(method.toLowerCase())) {
chain.doFilter(req, res);
return;
}
for (String hdr : headers) {
if (!m_lstAllowedHeaders.contains(hdr.toLowerCase())) {
chain.doFilter(req, res);
return;
}
}
res.setHeader("Access-Control-Allow-Methods", m_allowedMethods);
res.setHeader("Access-Control-Allow-Headers", m_allowedHeaders);
res.setHeader("Access-Control-Max-Age", m_preflightMaxAge);
}
res.setHeader("Access-Control-Allow-Origin", origin);
if (m_supportCredentials) {
res.setHeader("Access-Control-Allow-Credentials", "true");
}
}
chain.doFilter(req, res);
}

@Override
public void destroy() {

}

private boolean match(String url, String pattern) {
return pattern.equals("*") || url.equals(pattern);
}
}

web.xml配置如下：

!--跨域访问过滤器-->

CorsFilter
com.gysoft.utils.cros.CorsFilter

cors.allowed.origins
*


cors.allowed.methods
GET,POST,HEAD,OPTIONS,PUT,DELETE


cors.allowed.headers

Content-Type,X-Requested-With,accept,Origin,Access-Control-Request-Method,Access-Control-Request-Headers



cors.support.credentials
true


cors.preflight.maxage
3600



CorsFilter
/*