How to use JavaScript in jsp pages

JSP (Java Server Pages) is a server-side web development framework based on Java technology that can be used to build dynamic websites and web applications. JSP has a rich set of Java libraries and tools that help developers build high-quality web applications quickly and efficiently. However, one problem many developers run into when building websites using JSP is how to use JavaScript.

JavaScript is a powerful client-side programming language used to add interactivity and dynamics to websites. JavaScript can be used to validate forms, modify elements in HTML, implement animation effects, and other functions. However, because JSP is a Java program running on the server side and cannot directly call JavaScript in the client browser, many developers believe that JSP cannot use JavaScript.

However, in fact, JSP can use JavaScript. JSP provides many ways to use JavaScript, let's look at each of these methods one by one.

1. Embed JavaScript code directly in the JSP page

This is the simplest and most common way. Use the script tag to embed JavaScript code in the JSP page, as shown below:

  <title>JSP 中使用 JavaScript</title>


  <h1 id="欢迎来到我的网站">欢迎来到我的网站</h1>
  <script>
    // 在这里编写 JavaScript 代码
    alert("Hello World!");
  </script>

Using this method, you can write JavaScript code directly in the JSP page to implement various functions.

2. Define functions in external JavaScript files and call them in JSP pages

JSP pages can call JavaScript functions by linking to external JavaScript files. This approach avoids embedding a lot of JavaScript code in the page and makes the code easier to maintain.

Define the function in the external JavaScript file:

// 引用外部 JavaScript 文件
function sayHello() {
  alert("Hello World!");
}

Call the above function in the JSP page:

  <title>JSP 中使用 JavaScript</title>
  <script></script>


  <h1 id="欢迎来到我的网站">欢迎来到我的网站</h1>
  <button>点击这里</button>

The onclick attribute of HTML is used here to call the function. When the user clicks button, a dialog box will pop up showing "Hello World!".

3. Use AJAX technology in JSP to call server-side Java methods

AJAX is the abbreviation of Asynchronous JavaScript and XML, which refers to the use of JavaScript and XML technology without refreshing the entire A technology that updates part of the page content in case of a page. Through AJAX technology, JSP pages can call server-side Java methods to achieve some advanced functions. The following is a simple example:

Define a Java class:

public class MyUtil {
  public static String getData() {
    // 这里返回一些数据
    return "some data";
  }
}

Define a piece of JavaScript code in the JSP page:

function getData() {
  var xhr = new XMLHttpRequest();
  xhr.onreadystatechange = function() {
    if (xhr.readyState == 4 && xhr.status == 200) {
      var data = xhr.responseText;
      // 处理返回的数据
      alert(data);
    }
  }
  xhr.open("GET", "MyServlet", true);
  xhr.send();
}

Call the above JavaScript function in the JSP page:

  <title>JSP 中使用 JavaScript</title>


  <h1 id="欢迎来到我的网站">欢迎来到我的网站</h1>
  <button>获取数据</button>

In this example, a JavaScript function getData() is defined in the JSP page, which calls the server-side Java method MyUtil.getData() through AJAX technology and displays the returned data in a dialog box.

The above are the three methods of using JavaScript in JSP. Developers can choose the most appropriate method based on the specific situation. Although JSP cannot directly call JavaScript in the browser, through the above methods, JSP can still easily achieve various powerful interactions and dynamic effects.

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