java - 如果忽略发生返回其他内容？

Question

package utils;

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class Urlpicture {

    public String get_main_url(int num) {
        String jpgurl = null;
    try{
        String url = "https://www.zigbang.com/items1/"+num; 
        jpgurl = "http://z1.zigbang.com/items/7697786/538ec7a16033f0c32eac29ac50deb04a1e6bf3ba.jpg?h=800&q=60";
        Document doc = Jsoup.connect(url).get();    // this part require try catch
        jpgurl = doc.select("img[src$=.jpg?h=800&q=60]").get(0).absUrl("src");



        System.out.println(url);
        System.out.println(jpgurl);

    }catch(Exception e){
        e.printStackTrace();
    }
    return jpgurl;




    }


}

从 Jsoup Connect 获取文档。但如果 Jsoup.connect 给出错误。我想要jgurl 作为其他东西并继续运行代码。这不可能吗？(此代码将从外部调用多次，但如果发生一个异常，它就会停止)

外部源调用此 urlpicture

    @RequestMapping("/search")
    public ModelAndView searchHandler() throws JsonProcessingException {
        ModelAndView mav = new ModelAndView("t_search");

        List<HashMap<String, Object>> mlist = rd.test_room();


//=====================================================  
        List<String> urlcol = new ArrayList<>();
          JSONArray json_arr=new JSONArray();// 
            for (Map<String, Object> map : mlist) {
                JSONObject json_obj=new JSONObject();
                String url = null;
                System.out.println(map.get("SELL_NUM"));
                int num = Integer.parseInt(map.get("SELL_NUM")+"");
                String str = (urp.get_main_url(num).toString());// this calling the function
                System.out.println(str);
       }
                   urlcol.add(url);
                for (Map.Entry<String, Object> entry : map.entrySet()) {
                    String key = entry.getKey();

                    Object value = entry.getValue();


                    try {

                        json_obj.put(key,value);
                    } catch (Exception e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }                           
                }
                (json_arr).put(json_obj);

           }

================================================== ============修复后

@RequestMapping("/search")
    public ModelAndView searchHandler() throws JsonProcessingException {
        ModelAndView mav = new ModelAndView("t_search");

        List<HashMap<String, Object>> mlist = rd.test_room();



        List<String> urlcol = new ArrayList<>();
          JSONArray json_arr=new JSONArray();
            for (Map<String, Object> map : mlist) {
                JSONObject json_obj=new JSONObject();
                String url = null;
                String input = null;
                System.out.println(map.get("SELL_NUM"));
                int num = 0;
                num = Integer.parseInt(map.get("SELL_NUM")+"");
                input = "https://www.zigbang.com/items1/"+num; 
                System.out.println(input);

              try{
                url= (urp.get_main_url(input));
                System.out.println(url);

              }catch(Exception e){
                  System.out.println("No=");
                  e.printStackTrace();
                  url = "http://z1.zigbang.com/items/7697786/538ec7a16033f0c32eac29ac50deb04a1e6bf3ba.jpg?h=800&q=60";

}

@Service
public class Urlpicture {

    public String get_main_url(String url) {
        Document doc;
        String jpgurl = null;
    try{

        jpgurl = "http://z1.zigbang.com/items/7697786/538ec7a16033f0c32eac29ac50deb04a1e6bf3ba.jpg?h=800&q=60";
        jpgurl = Jsoup.connect(url).get().select("img[src$=.jpg?h=800&q=60]").get(0).absUrl("src"); 


    }catch(Exception e){
        e.printStackTrace();

    }finally{

        return jpgurl;
    }

================================================== =====================修复后，异常后继续运行。但即使 url 链接存在且编号有效它返回所有值作为异常。

7666495
https://www.zigbang.com/items1/7666495// this link is valid but throw exception
No=
java.lang.NullPointerException
    at controller.main_controller.searchHandler(main_controller.java:54)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.springf

我不知道为什么这会不断抛出所有值的异常

Answer 1

问题出在 jgurl 变量的范围上，您需要在 try block 之前声明该变量，如下所示。

此外，要解决第二个问题，您需要将下载图像逻辑提取到单独的方法中，并在未找到给定 的图像时使用默认的 num 再次调用它num，也如下所示:

public String get_main_url(int num) {
        int num = 7453201;
        String jpgurl  = null;
        try {
            downloadImage(num);
        } catch (Exception e) {
            e.printStackTrace();
            num=0;//set the default value for which img exists
            downloadImage(num);//call downloadImage with default num
        }
    }

private String downloadImage(int num) {
     String url = "https://www.zigbang.com/items1/"+num; 
     System.out.println(url);
     Document doc = Jsoup.connect(url).get();
     jpgurl = doc.select("img[src$=.jpg?h=800&q=60]").get(0).absUrl("src");
     System.out.println(i + "="+jpgurl);
}