要在AEM 6.5中的Sites目录中显示缩略图，你可以使用以下代码示例来解决问题：

1. 首先，你需要创建一个Java Servlet来生成缩略图。在该Servlet中，你可以使用Apache Sling Imaging API来生成缩略图。

import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.api.SlingHttpServletResponse;
import org.apache.sling.api.servlets.SlingSafeMethodsServlet;
import org.apache.sling.api.resource.Resource;
import org.apache.sling.api.resource.ResourceResolver;
import org.apache.sling.api.resource.ResourceResolverFactory;
import org.apache.sling.servlets.annotations.SlingServletResourceTypes;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.annotations.Reference;

import javax.imageio.ImageIO;
import javax.servlet.Servlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletResponse;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

@Component(service = Servlet.class)
@SlingServletResourceTypes(
        resourceTypes = "sling/servlet/default",
        selectors = "thumbnail",
        extensions = "jpg",
        methods = "GET"
)
public class ThumbnailServlet extends SlingSafeMethodsServlet {

    @Reference
    private ResourceResolverFactory resourceResolverFactory;

    @Override
    protected void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response) throws ServletException, IOException {
        // 获取图片资源路径
        String imagePath = request.getParameter("path");

        ResourceResolver resourceResolver = null;
        InputStream inputStream = null;
        OutputStream outputStream = null;

        try {
            // 获取ResourceResolver
            resourceResolver = resourceResolverFactory.getServiceResourceResolver(null);
            Resource imageResource = resourceResolver.getResource(imagePath);

            if (imageResource != null) {
                // 读取原始图片
                inputStream = imageResource.adaptTo(InputStream.class);
                BufferedImage image = ImageIO.read(inputStream);

                if (image != null) {
                    // 生成缩略图
                    BufferedImage thumbnail = Scalr.resize(image, 100);
                    
                    // 设置响应类型为JPEG
                    response.setContentType("image/jpeg");

                    // 将缩略图输出到响应流
                    outputStream = response.getOutputStream();
                    ImageIO.write(thumbnail, "jpeg", outputStream);
                }
            }
        } catch (Exception e) {
            // 处理异常
            response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
        } finally {
            // 关闭流和释放资源
            if (inputStream != null) {
                inputStream.close();
            }
            if (outputStream != null) {
                outputStream.close();
            }
            if (resourceResolver != null) {
                resourceResolver.close();
            }
        }
    }
}

2. 接下来，你需要在Felix控制台中配置OSGi组件以启用此Servlet。在Felix控制台中，创建一个新的OSGi配置并添加以下属性：

• 名称：Thumbnail Servlet
• 类：你创建的Java Servlet的完全限定类名（例如：com.example.ThumbnailServlet）
• 资源类型：sling/servlet/default
• 选择器：thumbnail
• 扩展名：jpg
• 方法：GET

3. 保存配置并重新启动AEM。

现在，当你在Sites目录中访问图片资源时，可以使用以下URL来获取缩略图：

/sites.html/content/dam/path/to/image.thumbnail.jpg

请替换path/to/image为实际的图片资源路径。你可以在浏览器中访问此URL以获取生成的缩略图。