javaWeb项目跨域问题解决方案：

1.简单的servlet项目

1.配置一个filter过滤器，过滤所有的请求，并且设置响应头

package Filter;

import javax.servlet.*;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/*自定义拦截器 用于给每个都加上跨域的头*/
public class CORSFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        //变成http的
        HttpServletResponse resp = (HttpServletResponse) response;
        // 添加参数，允许任意domain访问
        resp.setContentType("text/html;charset=UTF-8");
        //禁用缓存，确保网页信息是最新数据
        resp.setHeader("Pragma","No-cache");
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Access-Control-Allow-Origin", "*");
        resp.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, HEAD, DELETE, PUT");
        resp.setHeader("Access-Control-Max-Age", "3600");
        resp.setHeader("Access-Control-Allow-Headers",
                "X-Requested-With, Content-Type, Authorization, Accept, Origin, User-Agent, Content-Range, Content-Disposition, Content-Description");

        resp.setDateHeader("Expires", -10);
        chain.doFilter(request, resp);
    }
    public void init(FilterConfig filterConfig) {}


    public void destroy() {}
}

2.在web.xml中声明该过滤器（注意：最好放在最前面）

<filter>
        <filter-name>cors</filter-name>
        <filter-class>Filter.CORSFilter</filter-class>
</filter>
<filter-mapping>
        <filter-name>cors</filter-name>
        <url-pattern>/*</url-pattern>
</filter-mapping>

3.然后就可以直接解决跨域问题了

　　2.使用springMVC下的跨域问题解决方案

1.先把整个springMVC项目搭建起来

　　1.1在pom.xml中引入maven依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">

  <modelVersion>4.0.0</modelVersion>
  <packaging>war</packaging>

  <name>smart_blog</name>
  <groupId>com.kylin</groupId>
  <artifactId>smart_blog</artifactId>
  <version>1.0-SNAPSHOT</version>

  <build>
    <plugins>
      <plugin>
        <groupId>org.mortbay.jetty</groupId>
        <artifactId>maven-jetty-plugin</artifactId>
        <version>6.1.7</version>
        <configuration>
          <connectors>
            <connector implementation="org.mortbay.jetty.nio.SelectChannelConnector">
              <port>8888</port>
              <maxIdleTime>30000</maxIdleTime>
            </connector>
          </connectors>
          <webAppSourceDirectory>${project.build.directory}/${pom.artifactId}-${pom.version}</webAppSourceDirectory>
          <contextPath>/</contextPath>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>6</source>
          <target>6</target>
        </configuration>
      </plugin>
    </plugins>
  </build>

  <dependencies>
    <!-- junit -->
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12-beta-3</version>
      <scope>test</scope>
    </dependency>
    <!-- log4j -->
    <dependency>
      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>1.2.17</version>
    </dependency>

    <dependency>
      <groupId>jstl</groupId>
      <artifactId>jstl</artifactId>
      <version>1.2</version>
    </dependency>

    <!-- spring 的基本依赖 开始 -->

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-core</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-expression</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-beans</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-aop</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context-support</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-tx</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-jdbc</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-aspects</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-tx</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-test</artifactId>
      <version>4.3.18.RELEASE</version>
    </dependency>
    <!-- spring 的基本依赖 结束 -->

    <!-- https://mvnrepository.com/artifact/javax.servlet.jsp/javax.servlet.jsp-api -->
    <dependency>
      <groupId>javax.servlet.jsp</groupId>
      <artifactId>javax.servlet.jsp-api</artifactId>
      <version>2.2.1</version>
      <scope>provided</scope>
    </dependency>
    <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>3.1.0</version>
      <scope>provided</scope>
    </dependency>

    <!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
    <dependency>
      <groupId>com.google.code.gson</groupId>
      <artifactId>gson</artifactId>
      <version>2.2.4</version>
    </dependency>

  </dependencies>

</project>

　　1.2编写springMVC的核心配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
            http://www.springframework.org/schema/context
            http://www.springframework.org/schema/context/spring-context-3.1.xsd
            http://www.springframework.org/schema/mvc
            http://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd">

    <!-- Enables the Spring MVC @Controller programming model -->
    <mvc:annotation-driven />

    <context:component-scan base-package="com.kylin.Controller" />



    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/" />
        <property name="suffix" value=".jsp" />
    </bean>

</beans>

　　1.3在web.xml中进行基本配置

<?xml version="1.0" encoding="UTF-8"?>

<web-app version="2.4"
         xmlns="http://java.sun.com/xml/ns/j2ee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
  <filter>
    <filter-name>CORSFilter</filter-name>
    <filter-class>com.kylin.Filter.CORSFilter</filter-class>
  </filter>

  <filter-mapping>
    <filter-name>CORSFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

  <!--拦截器的配置-->



  <!--前端控制器的配置-->
  <servlet>
    <servlet-name>springMVC</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <!--配置核心配置文件的位置-->
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath:spring/springMVC.xml</param-value>
    </init-param>
    <!--随服务器启动而启动-->
    <load-on-startup>1</load-on-startup>
  </servlet>
  
  <servlet-mapping>
    <servlet-name>springMVC</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>

</web-app>

2.编写过滤器CORSFilter来处理跨域问题

package com.kylin.Filter;

import javax.servlet.*;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/*自定义拦截器 用于给每个都加上跨域的头*/
public class CORSFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        //变成http的
        HttpServletResponse resp = (HttpServletResponse) response;
        // 添加参数，允许任意domain访问
        resp.setContentType("text/html;charset=UTF-8");
        //禁用缓存，确保网页信息是最新数据
        resp.setHeader("Pragma","No-cache");
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Access-Control-Allow-Origin", "*");
        resp.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, HEAD, DELETE, PUT");
        resp.setHeader("Access-Control-Max-Age", "3600");
        resp.setHeader("Access-Control-Allow-Headers",
                "X-Requested-With, Content-Type, Authorization, Accept, Origin, User-Agent, Content-Range, Content-Disposition, Content-Description");

        resp.setDateHeader("Expires", -10);
        chain.doFilter(request, resp);
    }
    public void init(FilterConfig filterConfig) {}


    public void destroy() {}
}

3.在web.xml中声明该过滤器(注意：位置最好放在最前面)

　　由于web.xml中上面已经有了，就不再重复拷贝代码

4.就能正常的解决跨域问题

下面附上项目的目录结构：

附上前端vue框架的代码：

　　ps：前端vue框架刚刚学，很多东西不懂~别介意

附上项目目录：

1.在config/index.js中配置代理

2.在router/index.js中配置路由

3.在组件中使用axios来发送post请求

src/components/Login.vue

<template>
  <div class="Login">
    <input type="tel" placeholder="innput your phone...." v-model="phone">
    <input type="password" placeholder="input your password" v-model="password">
    <button @click="postMethod">提交</button>
  </div>
</template>

<script>
import axios from 'axios'
export default {
  name: 'Login',
  data () {
    return {
      phone:'',
      password:'',
    }
  },
  methods:{
    postMethod:function(){
      axios.post('http://192.168.253.13:8080/smart_blog/user',{
        phone:this.phone,
        password:this.password,
      })
      .then(function(res){
        console.log(res)
        // alert(res.data.message)
        alert(res.data.status)
      })
      .catch(function(err){
        console.log(err)
      })
    }
  }
  

}
</script>

<!-- Add "scoped" attribute to limit CSS to this component only -->
<style scoped>
</style>

4.打开vue项目所在的目录，输入npm start命令启动项目即可

5.开心的实现前后端分离~~~~~

来源：oschina

链接：https://my.oschina.net/u/2331760/blog/2960965

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