Java implements cross-domain request and data transmission of form data

Java implements cross-domain request and data transmission of form data

In modern web development, cross-domain request is a common problem, especially when we use Java to process form data. This article will introduce how to use Java to implement cross-domain requests and data transmission of form data to solve this problem, and provide relevant code examples.

1. What is a cross-domain request?
Cross-domain request refers to requesting resources under another domain name from a web page under one domain name, and the browser’s standard same-origin policy prohibits such cross-domain requests. of. The same-origin policy was established to protect user privacy and website security, but in some scenarios, we do need to implement cross-domain requests, such as separate development of front-end and back-end, and use different domain names and ports for front-end development.

2. Ways to solve cross-domain requests
In Java, there are many ways to solve the problem of cross-domain requests. Two common ways will be introduced below.

1. JSONP
   JSONP is a cross-domain request that uses the feature of the <script> tag to load resources across domains. On the server side, we need to wrap the returned data into a function call and then pass the function as a parameter to the caller. The caller can receive the returned data by defining a global callback function. </script>

The following is a sample code that uses JSONP to implement cross-domain requests. Assume that the interface address of the server is http://server.com/api, and the domain name of the front-end page is http://client.com.

// 前端代码
function processData(data) {
  // 处理返回的数据
}

var script = document.createElement('script');
script.src = 'http://server.com/api?callback=processData';
document.head.appendChild(script);

// 服务端代码
String callback = request.getParameter("callback");
String data = "{"name": "Alice", "age": 20}";
String result = callback + "(" + data + ")";
response.getWriter().write(result);

2. CORS
   CORS is the abbreviation of Cross-Origin Resource Sharing. It is a cross-domain request method implemented by setting response headers on the server side. On the server side, we need to set Access-Control-Allow-Origin and other related response headers to allow specific domain names to make cross-domain requests.

The following is a sample code that uses CORS to implement cross-domain requests. Assume that the domain name of the front-end page is http://client.com and the interface address of the server is http://server.com/api.

// 前端代码
var xhr = new XMLHttpRequest();
xhr.open('GET', 'http://server.com/api');
xhr.onreadystatechange = function () {
  if (xhr.readyState === XMLHttpRequest.DONE) {
    if (xhr.status === 200) {
      var data = JSON.parse(xhr.responseText);
      // 处理返回的数据
    }
  }
};
xhr.send();

// 服务端代码
response.setHeader("Access-Control-Allow-Origin", "http://client.com");
String data = "{"name": "Alice", "age": 20}";
response.getWriter().write(data);

3. Summary
The above is how to use Java to implement cross-domain requests and data transmission of form data. We can choose the appropriate method to solve the problem of cross-domain requests based on specific scenarios and needs. Whether using JSONP or CORS, they are common and effective solutions.

I hope this article will be helpful to you. If you have any questions, please feel free to leave a message for consultation. thanks for reading!

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