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I am using WDCalendar in Struts2. I was converting Hashmap to Json String using GSON, but all of a sudden, i am getting NULL pointer exception while conveting Hashmap to JSON String

result = new Gson().toJson(ret);

My Code :

public static String loadAllEvents(String start, String end) throws SQLException {
        PreparedStatement ps1 = null;
        ResultSet rs1 = null;
        Gson gson = new Gson();
        String result = "";
        Connection con = ULDBConnectionUtility.getDBConnection();
        HashMap<String, Object> ret = new HashMap<String, Object>();




        try{
            String strSql = "SELECT * FROM EVENT_MANAGER";// WHERE START_DATE BETWEEN '"+start+"' AND '"+end+"'";           
            ps1 = con.prepareStatement(strSql);
            rs1  = ps1.executeQuery();

            SimpleDateFormat fromDB = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
            java.text.SimpleDateFormat sourceFormat = new SimpleDateFormat("EEE MMM dd yyyy HH:mm:ss ZZZ");


            ArrayList<ArrayList> eventArrayList = new ArrayList<ArrayList>();
            while(rs1.next()){              
                ArrayList EvtData = new ArrayList();
                EvtData.add(rs1.getInt("EVENT_ID"));//0
                EvtData.add(rs1.getString("EVENT_TITLE"));//1
                EvtData.add(sourceFormat.format(fromDB.parse(rs1.getString("START_DATE"))));//2
                EvtData.add(sourceFormat.format(fromDB.parse(rs1.getString("END_DATE"))));//3
                EvtData.add(rs1.getInt("IS_ALL_DAY_EVENT"));//4
                EvtData.add(Integer.parseInt("0"));//5
                EvtData.add(rs1.getInt("RECURRING_RULE"));//6
                EvtData.add(rs1.getString("COLOR"));//7
                EvtData.add(Integer.parseInt("1"));//8
                EvtData.add(rs1.getString("LOCATION"));//9
                EvtData.add("");//10
                eventArrayList.add(EvtData);
            }
            String error = "";
             ret.put("events", eventArrayList);
             ret.put("issort", true);
             ret.put("start", sourceFormat.format(fromDB.parse(start)));
             ret.put("end", sourceFormat.format(fromDB.parse(end)));
             ret.put("error", error);
             System.out.println("ret : "+ret);
             result = new Gson().toJson(ret);

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (rs1 != null) {
                    rs1.close();
                }
                if (ps1 != null) {
                    ps1.close();
                }
                if (con != null) {
                    con.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        return result;
    }

HashMap before passing to convertion:

{events=[[98, EvebtTitle, Mon Dec 03 2012 10:45:00 +0530, Wed Oct 17 2012 11:15:00 +0530, 0, 0, 0, 0, 1, NJ, ], [118, testDec, Wed Dec 05 2012 09:00:00 +0530, Wed Dec 05 2012 10:00:00 +0530, 0, 0, 0, null, 1, null, ], [67, Test45, Wed Dec 05 2012 10:30:00 +0530, Tue Oct 16 2012 11:00:00 +0530, 1, 0, 0, 0, 1, NY, ], [119, sd, Tue Dec 04 2012 00:00:00 +0530, Tue Dec 04 2012 00:00:00 +0530, 1, 0, 0, null, 1, null, ], [78, Test, Fri Dec 07 2012 09:30:00 +0530, Mon Oct 15 2012 10:15:00 +0530, 0, 0, 0, 1, 1, LA, ], [66, Event 2, Tue Dec 04 2012 10:00:00 +0530, Tue Oct 16 2012 10:30:00 +0530, 0, 0, 1, 0, 1, CA, ]], start=Thu Jan 01 1970 05:30:00 +0530, issort=true, end=Thu Jan 01 1970 05:30:00 +0530, error=null}

Error:

20:49:15,597 ERROR [STDERR] java.lang.NullPointerException
20:49:15,599 ERROR [STDERR]     at com.google.gson.DefaultTypeAdapters$CollectionTypeAdapter.serialize(DefaultTypeAdapters.java:443)
20:49:15,601 ERROR [STDERR]     at com.google.gson.DefaultTypeAdapters$CollectionTypeAdapter.serialize(DefaultTypeAdapters.java:430)
20:49:15,604 ERROR [STDERR]     at com.google.gson.JsonSerializationVisitor.visitUsingCustomHandler(JsonSerializationVisitor.java:128)
20:49:15,605 ERROR [STDERR]     at com.google.gson.ObjectNavigator.accept(ObjectNavigator.java:96)
20:49:15,606 ERROR [STDERR]     at com.google.gson.JsonSerializationContextDefault.serialize(JsonSerializationContextDefault.java:47)
20:49:15,608 ERROR [STDERR]     at com.google.gson.DefaultTypeAdapters$CollectionTypeAdapter.serialize(DefaultTypeAdapters.java:445)
20:49:15,609 ERROR [STDERR]     at com.google.gson.DefaultTypeAdapters$CollectionTypeAdapter.serialize(DefaultTypeAdapters.java:430)
20:49:15,610 ERROR [STDERR]     at com.google.gson.JsonSerializationVisitor.visitUsingCustomHandler(JsonSerializationVisitor.java:128)
20:49:15,611 ERROR [STDERR]     at com.google.gson.ObjectNavigator.accept(ObjectNavigator.java:96)
20:49:15,612 ERROR [STDERR]     at com.google.gson.JsonSerializationContextDefault.serialize(JsonSerializationContextDefault.java:47)
20:49:15,613 ERROR [STDERR]     at com.google.gson.DefaultTypeAdapters$MapTypeAdapter.serialize(DefaultTypeAdapters.java:509)
20:49:15,613 ERROR [STDERR]     at com.google.gson.DefaultTypeAdapters$MapTypeAdapter.serialize(DefaultTypeAdapters.java:489)
20:49:15,614 ERROR [STDERR]     at com.google.gson.JsonSerializationVisitor.visitUsingCustomHandler(JsonSerializationVisitor.java:128)
20:49:15,615 ERROR [STDERR]     at com.google.gson.ObjectNavigator.accept(ObjectNavigator.java:96)
20:49:15,616 ERROR [STDERR]     at com.google.gson.JsonSerializationContextDefault.serialize(JsonSerializationContextDefault.java:47)
20:49:15,617 ERROR [STDERR]     at com.google.gson.Gson.toJson(Gson.java:269)
20:49:15,618 ERROR [STDERR]     at com.google.gson.Gson.toJson(Gson.java:220)
20:49:15,618 ERROR [STDERR]     at com.google.gson.Gson.toJson(Gson.java:200)
20:49:15,619 ERROR [STDERR]     at dao.UtilityDao.loadAllEvents(UtilityDao.java:174)
20:49:15,620 ERROR [STDERR]     at utility.CalendarUtility.loadAllList(CalendarUtility.java:64)
20:49:15,621 ERROR [STDERR]     at servlet.DataFeed.doGet(DataFeed.java:56)
20:49:15,622 ERROR [STDERR]     at servlet.DataFeed.doPost(DataFeed.java:97)
20:49:15,623 ERROR [STDERR]     at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
20:49:15,624 ERROR [STDERR]     at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
20:49:15,625 ERROR [STDERR]     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
20:49:15,626 ERROR [STDERR]     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
20:49:15,627 ERROR [STDERR]     at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
20:49:15,
4

2 回答 2

1

解决了：

一些事件字段值在 DB 中为 NULL，这就是原因。

在ret.put("events", eventArrayList);

eventArrayList 引用ArrayList<ArrayList>并且很少有字段值为<ArrayList>NULL，

从上面的示例：（查看位于第二个索引的内部数组列表中的 Null 值）

{events=[[98, EvebtTitle, Mon Dec 03 2012 10:45:00 +0530, Wed Oct 17 2012 11:15:00 +0530, 0, 0, 0, 0, 1, NJ, ], [118, testDec, Wed Dec 05 2012 09:00:00 +0530, Wed Dec 05 2012 10:00:00 +0530, 0, 0, 0, null, 1, null, ]]}

从内部 ArrayList 中删除 Null 值后，一切正常。

于 2012-12-03T16:13:41.393 回答
0

关于方法我想到的一件事

public String toJson(Object src)

是GSON 文档，其中指出“当指定的对象不是泛型类型时，应使用此方法。如果对象是泛型类型，请改用 toJson(Object, Type)。”

另一件事是空指针异常可能是由任何其他对象引起的，而不是特别是HashMap。您似乎认为这是理所当然的，但我建议您调试代码。

于 2012-12-03T15:37:30.497 回答