Using cpolar for Java SpringBoot API Testing and Fixed Public Tunnels

Preface

In a front‑back separation project, you can use cpolar's internal‑network penetration to simulate a public network environment for remote debugging of local service interfaces; this tutorial uses a Java backend API as an example.

1. Local Environment Setup

1.1 Environment Parameters

JDK 1.8

IDEA

SpringBoot

Maven

Tomcat 9.0

Postman

1.2 Build a SpringBoot Service Project

Create a SpringBoot project and implement a simple POST interface for demonstration.

@RestController
@RequestMapping("/test")
public class InterfaceTest {
    /**
     * Test interface
     * @param data
     * @return Map
*/
    @PostMapping("/interTest")
    public Map
interTest(@RequestBody Map
data){
        System.out.println(data);
        if (data.size()>0){
            return data;
        }
        data.put("code","404");
        return data;
    }
}

2. Internal Network Penetration

We use cpolar , which supports HTTP/HTTPS/TCP, has no traffic limit, and does not require a public IP.

2.1 Install and Configure cpolar

Official website: https://www.cpolar.com/

2.1.1 Windows

Download the Windows version from the website and install with default settings.

2.1.2 Linux

Domestic installation:

curl -L https://www.cpolar.com/static/downloads/install-release-cpolar.sh | sudo bash

Overseas short‑link installation:

curl -sL https://git.io/cpolar | sudo bash

Check version to confirm successful installation:

cpolar version

Token authentication: obtain your token from the cpolar console and run:

cpolar authtoken xxxxxxx

Simple tunnel test:

cpolar http 8080

Press Ctrl+C to exit.

Add cpolar as a system service:

sudo systemctl enable cpolar

Start the service:

sudo systemctl start cpolar

Check service status (image omitted).

2.2 Create Tunnel Mapping for Local Port

After installing cpolar, open the browser to http://localhost:9200 and log in to the cpolar web UI.

In the dashboard, go to Tunnel Management → Create Tunnel and set up an HTTP tunnel for the local Tomcat port 8080.

Tunnel name: custom (avoid duplicates)

Protocol: HTTP

Local address: 8080

Domain type: free random domain

Region: China VIP

After creation, view the generated public address in the Online Tunnel List and copy it.

2.3 Test Public Address

Use Postman to send a POST request to the copied public address plus the API path, with JSON parameters. Debug the service to verify the request reaches the interface.

3. Fixed Public Address

The random public address created by cpolar changes within 24 hours, which is inconvenient for long‑term remote access. You can reserve a secondary sub‑domain to obtain a fixed address.

Note: you need to upgrade the cpolar plan to at least the Basic tier; each tier provides different bandwidth. (cpolar.cn is already备案)

3.1 Reserve a Sub‑Domain

Log in to cpolar, go to the Reserve section, choose a secondary sub‑domain, set a name, and reserve it. Copy the reserved sub‑domain name after success.

3.2 Configure the Sub‑Domain

In the cpolar web UI, edit the previously created 8080 tunnel and set the Domain Type to "Secondary Sub‑Domain" and fill in the reserved sub‑domain (e.g., test01). Click Update.

Domain Type: Secondary Sub‑Domain

Sub Domain: test01

After updating, the online tunnel list shows the new fixed public address; copy it.

3.2 Test Using Fixed Public Address

In Postman, call the fixed HTTP address. Debug the backend to confirm the request reaches the interface.

4. cpolar Listener

You can open the cpolar listener at http://localhost:4040 to view request logs, replay requests, and accelerate testing.

4.1 Enable Listening

Select the configured HTTP tunnel, edit it, and enable the listener in Advanced Settings.

4.2 Request Listening

Visit http://localhost:4040 in a browser. After sending a request to the backend, the listener displays request method, data, path, status, and result, greatly improving debugging efficiency.

Backend Exclusive Technical Group

Build a high‑quality technical community; developers, recruiters, and anyone interested are welcome to join, share job referrals, and help each other improve.

Maintain civil discussion, focusing on technical exchange , job referrals , and industry topics .

Advertisements are prohibited; beware of private scams.