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Using Velocity for Web template engine processing in Java API development

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Release： 2023-06-18 13:19:40

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Using Velocity for Web template engine processing in Java API development

With the continuous development of the Internet and Web technology, the development and maintenance of Web applications has become an increasingly important task. One of the most common elements in web applications is the template, the display part of the front-end interface. In the development of Java Web applications, it is often necessary to use a Web template engine to process these templates to obtain better effects and higher maintainability. This article will introduce the methods and techniques of using Velocity for Web template engine processing in Java API development.

1. Overview

Velocity is a Java-based template engine framework that can be used to generate various text files, including HTML, CSS, JavaScript, XML, etc. It combines data and templates to generate dynamic web content. The advantage of Velocity over other template engine frameworks is its ease of use and flexibility. Templates can be easily modified and customized, while having high performance and scalability.

In Java Web applications, the steps for using Velocity for template processing are as follows:

1. Define the template: Use the Velocity template language to write a template file, usually ending with ".vm".

2. Pass data: Pass the data to the template and let the template render based on the data.

3. Rendering templates: Use Velocity to render templates and generate HTML pages.

This article will introduce in detail how to implement these steps.

2. Define templates

In Velocity, you can use the template language to write template files. The template language is similar to HTML and can implement loops, conditional judgments, variable assignments and other functions. Here is a simple Velocity template example:

<!DOCTYPE html>
<html>
<head>
    <title>$title</title>
</head>
<body>
    <h1>$header</h1>
    <ul>
        #foreach($item in $items)
            <li>$item</li>
        #end
    </ul>
</body>
</html>

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In this template, use the $ notation to represent variables that can be replaced with actual values when the template is rendered. For example, $title represents the document title, $header represents the page title, $items represents the list item array, and the display method uses the template language loop structure in Velocity: #foreach($item in $items).

Velocity template language also supports common functions such as conditional judgment and variable assignment. For detailed syntax, please refer to official documents or other tutorials. In actual use, you can freely define the template structure and style to meet your needs.

3. Pass data

In web applications, it is usually necessary to obtain data from a database, back-end service or other data source, and pass this data to the template for rendering. In Java, you can use JavaBeans, Maps, or other data structures to encapsulate data and pass it to Velocity for rendering.

For example, in the following code, a JavaBean class Person is first defined, and then the VelocityContext class is used to encapsulate the JavaBean and other data, and these data are passed to The template is rendered.

public class Person {
    private String name;
    private int age;
    // getters and setters
}

public static void main(String[] args) {
    // 创建 Velocity 引擎
    VelocityEngine engine = new VelocityEngine();
    engine.init();

    // 创建 Velocity 上下文
    VelocityContext context = new VelocityContext();
    Person person = new Person();
    person.setName("Alice");
    person.setAge(18);
    context.put("person", person);
    context.put("title", "Hello World");

    // 输出渲染结果
    StringWriter writer = new StringWriter();
    engine.mergeTemplate("template.vm", "UTF-8", context, writer);
    System.out.println(writer.toString());
}

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In the above code, a Velocity engine instance is first created, then a Velocity context instance is created, and JavaBeans and other data are stored in the context to pass to the template for rendering. Finally, use the StringWriter class to output the rendered string content.

4. Rendering templates

Velocity provides the VelocityEngine class for template rendering. The basic method of rendering a template is as follows:

StringWriter writer = new StringWriter();
engine.mergeTemplate("template.vm", "UTF-8", context, writer);
String result = writer.toString();

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Among them, in the mergeTemplate method, the first parameter is the template file name, the second parameter is the file encoding, and the third parameter is Velocity Context, the fourth parameter is the output stream. The template file name can be an absolute path or a relative path, and the encoding is generally "UTF-8" or "ISO-8859-1". The Velocity context contains the data that needs to be rendered, and the output stream writes the rendering results to a string or file. Of course, you can also perform more advanced template processing through other methods provided by Velocity, such as caching, template parsing, etc.

5. Summary

Using Velocity for Web template engine processing is a very common development model in Java API development. It can make web applications more flexible and easier to maintain, improve development efficiency, and optimize web performance. This article introduces the basic usage methods and techniques of Velocity, hoping to provide help and guidance to Java developers in using Velocity for web development.

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