Solving Java cross-domain issues

How to solve the cross-domain access problem in Java development

In the current web application development, the trend of front-end and back-end separation is becoming more and more obvious. This means that the front-end and back-end code are handled by different development teams, and they usually run on different servers. However, due to browser security policies, cross-domain access will be restricted. Cross-domain access refers to requesting resources under another domain name from a web page under one domain name, such as requesting data from api.example.com from a page on www.example.com.

Java developers often encounter this problem during the development process: when the front-end code runs under one domain name, and the back-end interface runs under another domain name, how to solve the problem of cross-domain access? ? This article will introduce several commonly used solutions.

1. Allow cross-domain access through server settings
This is the most common method to solve cross-domain problems. Cross-domain problems can be solved by configuring on the backend server to allow specified domain names or IP addresses to access the interface. For example, in Java, you can set the allowed domain names by adding the following annotation on the Controller class:

@CrossOrigin(origins = "http://www.example.com")

In this way, the front-end page will no longer be subject to cross-domain restrictions when accessing the back-end interface.

2. Use JSONP (JSON with Padding)
JSONP is a simple-to-use cross-domain access solution. It creates a script tag in the front-end page, points to the back-end interface, and then wraps the returned data into a function call in the back-end. For example, the front-end page can call the back-end interface like this:

<script></p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:java;toolbar:false;'>function callback(data){ //处理返回的数据 }</pre><div class="contentsignin">Copy after login</div></div><p></script>

At this time, the data returned by the backend will be wrapped in the callback function, and the front-end page can obtain the data through the callback function.

3. Use a proxy server
Another common way to solve cross-domain problems is to use a proxy server. By adding a proxy server to the project, requests from the front-end page are forwarded to the domain name of the back-end interface. In this way, the front-end page can communicate with the back-end through the proxy server under the same domain name, avoiding cross-domain problems. Common proxy servers include Nginx and Apache.

4. Generate cross-domain resource sharing (CORS) response headers on the backend
CORS is a new mechanism in HTML5 to solve cross-domain access problems. By generating a CORS response header on the backend, you tell the browser that the interface can be accessed by the specified domain name. In Java, you can generate CORS response headers by adding the following annotation to the backend interface method:

@CrossOrigin(origins = "http://www.example.com")

5. Use the WebSocket protocol
The WebSocket protocol is a protocol for two-way communication on a single long-term connection. It can bypass the browser's same-origin policy and achieve cross-domain access. There are many mature WebSocket frameworks in Java, such as Netty and Tomcat's WebSocket implementation.

Summary:
There are many ways to solve cross-domain access problems in Java development. We can choose the appropriate solution according to the specific situation. Through server settings, JSONP, proxy server, CORS and WebSocket protocols, we can solve the cross-domain access problem in front-end and back-end separation development and improve the security and reliability of applications.

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