如何在AEM Servlet中读取OSGi配置值并实现排序返回

问题原因 #

你的Servlet执行到输出a1后停止，是因为调用property.get("Name1").toString()时触发了NullPointerException——OSGi配置元数据生成的属性键并非Java接口中的Name1，而是会自动转换为小写形式（如name1），用Name1作为键获取不到值，自然会抛出空指针异常，导致代码中断。

另外，直接使用ConfigurationAdmin读取配置并非AEM中获取OSGi服务配置的最佳实践，因为你已经封装了MyProjectServ服务，直接引用该服务会更简单、更安全。

解决方案一：修正ConfigurationAdmin的属性键名 #

如果你坚持使用ConfigurationAdmin，需要将属性键改为OSGi实际存储的名称（通常是方法名的小写）：

@Override
protected void doGet(final SlingHttpServletRequest req,
        final SlingHttpServletResponse resp) throws ServletException, IOException {
    resp.setContentType("text/plain");
    PrintWriter writer = resp.getWriter();
    
    try {
        Configuration config = MYPROJECT_CONFIG.getConfiguration(MY_PROJECT);
        Dictionary<String, Object> properties = config.getProperties();
        writer.write("a1");
        
        // 使用小写的键名获取配置值，增加空值判断避免空指针
        String first = properties.get("name1") != null ? properties.get("name1").toString() : "Abhinay";
        String second = properties.get("name2") != null ? properties.get("name2").toString() : "Pavan";
        String third = properties.get("name3") != null ? properties.get("name3").toString() : "Ram";
        
        writer.write("a2");
        writer.write(first);
        writer.write("a3");
        
        String[] names = {first, second, third};
        Arrays.sort(names);
        
        // 正确输出数组内容，替代默认的数组对象toString()
        for (String name : names) {
            writer.write(name + " ");
        }
    } catch (Exception e) {
        // 添加异常捕获，便于排查问题
        writer.write("Error: " + e.getMessage());
        e.printStackTrace();
    }
}

解决方案二：直接引用MyProjectServ服务（推荐） #

这是AEM中获取OSGi配置的标准方式，无需手动处理配置键名，直接通过服务调用获取值：

修正后的Servlet代码 #

package com.demo.training.core.servlets;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;

import javax.servlet.Servlet;
import javax.servlet.ServletException;

import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.api.SlingHttpServletResponse;
import org.apache.sling.api.servlets.HttpConstants;
import org.apache.sling.api.servlets.SlingAllMethodsServlet;
import org.osgi.framework.Constants;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.annotations.Reference;

import com.demo.training.core.services.MyProjectServ;

@Component(service = Servlet.class,
    property = {
        Constants.SERVICE_DESCRIPTION + "=Practice Servlet",
        "sling.servlet.methods=" + HttpConstants.METHOD_GET,
        "sling.servlet.methods=" + HttpConstants.METHOD_POST,
        "sling.servlet.paths=/bin/myproject",
        "sling.servlet.extensions=" + "txt"
    })
public class MyProjectServlet extends SlingAllMethodsServlet {
    private static final long serialVersionUID = 1L;

    // 直接引用你的OSGi服务
    @Reference
    private MyProjectServ myProjectServ;

    @Override
    protected void doGet(final SlingHttpServletRequest req,
            final SlingHttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/plain");
        PrintWriter writer = resp.getWriter();
        
        try {
            // 从服务中直接获取配置值
            String first = myProjectServ.getNAME1();
            String second = myProjectServ.getNAME2();
            String third = myProjectServ.getNAME3();
            
            writer.write("a2");
            writer.write(first);
            writer.write("a3");
            
            String[] names = {first, second, third};
            Arrays.sort(names);
            
            // 输出排序后的名称，用逗号分隔便于AJAX处理
            writer.write(String.join(",", names));
        } catch (Exception e) {
            writer.write("Error: " + e.getMessage());
            e.printStackTrace();
        }
    }
}

补充说明 #

1. 添加resp.setContentType("text/plain")确保响应类型正确，避免AJAX解析问题
2. 增加异常捕获，便于排查运行时错误
3. 使用String.join替代数组默认的toString()，输出更友好的字符串格式，方便前端AJAX处理

内容的提问来源于stack exchange，提问作者Abhinay up