在Java中使用Velocity模板引擎有以下幾種方法：

1. 使用Velocity的原始API：通過創建Velocity引擎實例，加載和渲染模板文件。以下是一個簡單的示例：

import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.Velocity;
import java.io.StringWriter;
public class VelocityExample {
public static void main(String[] args) {
// 初始化Velocity引擎
Velocity.init();
// 創建Velocity上下文
VelocityContext context = new VelocityContext();
context.put("name", "John Doe");
// 渲染模板
StringWriter writer = new StringWriter();
Velocity.mergeTemplate("template.vm", "UTF-8", context, writer);
// 輸出渲染結果
System.out.println(writer.toString());
}
}

2. 使用Velocity工具類：Velocity提供了一些實用的工具類來簡化模板渲染過程。以下是一個示例：

import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.Velocity;
import org.apache.velocity.tools.generic.DateTool;
import java.io.StringWriter;
public class VelocityExample {
public static void main(String[] args) {
// 初始化Velocity引擎
Velocity.init();
// 創建Velocity上下文
VelocityContext context = new VelocityContext();
context.put("name", "John Doe");
context.put("dateTool", new DateTool());
// 獲取模板
Template template = Velocity.getTemplate("template.vm", "UTF-8");
// 渲染模板
StringWriter writer = new StringWriter();
template.merge(context, writer);
// 輸出渲染結果
System.out.println(writer.toString());
}
}

3. 使用Velocity與Spring集成：如果你在Spring應用程序中使用Velocity，你可以通過配置VelocityConfigurer bean來集成Velocity。以下是一個示例：

import org.apache.velocity.app.VelocityEngine;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.ui.velocity.VelocityEngineFactoryBean;
@Configuration
public class VelocityConfig {
@Bean
public VelocityEngineFactoryBean velocityEngine() {
VelocityEngineFactoryBean factoryBean = new VelocityEngineFactoryBean();
factoryBean.setResourceLoaderPath("classpath:/templates/");
return factoryBean;
}
}

然后，你可以在Spring中注入VelocityEngine，并使用它來渲染模板。以下是一個示例：

import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.ui.velocity.VelocityEngineUtils;
@Component
public class VelocityService {
@Autowired
private VelocityEngine velocityEngine;
public String renderTemplate() {
VelocityContext context = new VelocityContext();
context.put("name", "John Doe");
Template template = velocityEngine.getTemplate("template.vm", "UTF-8");
return VelocityEngineUtils.mergeTemplateIntoString(velocityEngine, "template.vm", "UTF-8", context);
}
}