java reverse proxy forwarding requests

 

package com.example.demo;

import java.io.IOException;
import java.io.UnsupportedEncodingException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.io.IOUtils;
import org.apache.commons.lang.StringUtils;
import org.apache.http.HttpEntity;
import org.apache.http.HttpStatus;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;


@WebServlet(name = "firstServlet", urlPatterns = "/*")  //标记为servlet，以便启动器扫描。
public class FirstServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //resp.getWriter().append("firstServlet");
    	request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");

        String basePath = request.getScheme() + "://" + "ylbzj.nanyang.gov.cn";
        String locationUrl = basePath + request.getRequestURI();
        String queryValue = request.getQueryString();
        if (StringUtils.isNotBlank(queryValue)) {
            locationUrl += "?" + queryValue;
        }
       
        IOUtils.write(doGet(locationUrl), response.getOutputStream());

        
    }
    public static byte[] doGet(String locationUrl) {
        String result = null;
        //请求地址
       
      
       
        CloseableHttpClient httpclient = HttpClients.createDefault();
        CloseableHttpResponse response = null;
        String parameStr = null;
        try {
           
            //拼接参数
            StringBuffer sb = new StringBuffer();
            sb.append(locationUrl);
           
            //创建get请求
            HttpGet httpGet = new HttpGet(sb.toString());
             // 设置请求和传输超时时间  
            RequestConfig requestConfig = RequestConfig.custom()  
                    .setSocketTimeout(2000).setConnectTimeout(2000).build();  
            httpGet.setConfig(requestConfig);  
            // 提交参数发送请求
            response = httpclient.execute(httpGet);

            // 得到响应信息
            int statusCode = response.getStatusLine().getStatusCode();
            // 判断响应信息是否正确
            if (statusCode != HttpStatus.SC_OK) {
                // 终止并抛出异常
                httpGet.abort();
                throw new RuntimeException("HttpClient,error status code :" + statusCode);
            }
            HttpEntity entity = response.getEntity();
            if (entity != null) {
               return EntityUtils.toByteArray(entity);
              
               
            }
            EntityUtils.consume(entity);

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //关闭所有资源连接
            if (response != null) {
                try {
                    response.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (httpclient != null) {
                try {
                    httpclient.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
     
		return null;
       

    }

}

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.2.2.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>demo</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
 <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
            <version>4.5</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/commons-io/commons-io -->
<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.6</version>
</dependency>
        <!-- https://mvnrepository.com/artifact/org.apache.commons/commons-lang3 -->
<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.9</version>
</dependency>
        <!-- https://mvnrepository.com/artifact/commons-lang/commons-lang -->
<dependency>
    <groupId>commons-lang</groupId>
    <artifactId>commons-lang</artifactId>
    <version>2.6</version>
</dependency>
        
        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpcore</artifactId>
            <version>4.4.6</version>
        </dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
			<exclusions>
				<exclusion>
					<groupId>org.junit.vintage</groupId>
					<artifactId>junit-vintage-engine</artifactId>
				</exclusion>
			</exclusions>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

Learn  java to achieve reverse proxy server

 https://www.cnblogs.com/gj1990/p/8031255.html