Java - Vaadin - 表未填充

Question

这里有一点泡菜。我正在从 Zip 文件读取 JSON，并且想用 JSON 的内容填充 Vaadin 中的表格。

这是我的函数，用于读取内容并填充表格，这是 Java。

private void getJsonContent() {
        try {
            FileInputStream fis = new FileInputStream(backupFile);
            ZipInputStream zin = new ZipInputStream(new BufferedInputStream(fis));
            ZipEntry entry;
            byte[] buffer = new byte[1024];
            while((entry = zin.getNextEntry()) != null) {
                if(entry.getName().equalsIgnoreCase("content.json")) {
                    int n;
                    while((n = zin.read(buffer, 0, 1024)) > -1){
                        String JSON = new String(buffer, Charset.forName("UTF-8"));
                        JSONObject obj = new JSONObject(JSON);

                        logger.info(JSON);

                        // Assign "global" Values to Variables
                        this.createdAt = obj.getString("created_at");
                        this.version = obj.getString("version");

                        // Fill table if applicable                     
                        for(int i = 0; i < obj.getJSONArray("content").length(); i++) {
                            JSONObject sub = obj.getJSONArray("content").getJSONObject(i);
                            logger.info(sub);

                            infoTable.addItem(new Object[] {
                                    sub.get("imported_identities").toString(),
                                    sub.get("project_versions").toString(),
                                    sub.get("last_import").toString(),
                                    sub.get("client").toString(),
                                    sub.get("project").toString()
                            }, i +1);
                        }
                    }
                }
            }
            zin.close();
            fis.close();
        } catch (FileNotFoundException e) {
            // Can't happen here
        } catch (IOException e) {
            logger.info("Can't read File.");
        } catch (JSONException jse) {
            logger.info("JSON Content could not be read: " + jse.getMessage());
        }
    }

您会注意到我有一个函数调用 logger.info(sub) - 确保我得到的是另一个有效的 JSON 对象(我正在读取的文件包含嵌套的内容)

输出:

{"imported_identities":0,"project_versions":0,"last_import":null,"client":"Client1","project":"Project2"} 
{"imported_identities":0,"project_versions":0,"last_import":null,"client":"Client2","project":"Project1"}
{"imported_identities":0,"project_versions":1,"last_import":"2016-09-14T09:28:24.520Z","client":"Client1","project":"Project1"}

我确保所有值都是正确的(并且该表是使用 null 作为默认值构建的) - 这是表属性:

    infoTable.addContainerProperty(impIds, String.class, null);
    infoTable.addContainerProperty(projVe, String.class, null);
    infoTable.addContainerProperty(lstImp, String.class, null);
    infoTable.addContainerProperty(client, String.class, null);
    infoTable.addContainerProperty(projct, String.class, null);

    infoTable.setColumnCollapsingAllowed(true);
    infoTable.setColumnCollapsed(impIds, true);
    infoTable.setColumnCollapsed(projVe, true);
    infoTable.setColumnCollapsed(lstImp, true);

最后，表上调用了“refreshRowCache”。有人看到问题了吗？没有错误，什么也没有，表只是没有添加项目(调用后 infoTable.getItemIds().size() 的大小为 0。

编辑:

我尝试了以下方法来验证。

infoTable.addItem(i + 1);
infoTable.getItem(i + 1).getItemProperty(impIds).setValue(sub.get("imported_identities").toString());
infoTable.getItem(i + 1).getItemProperty(projVe).setValue(sub.get("project_versions").toString());

这导致了 NullPointerException，但是据我所知，堆栈跟踪不包含我的任何类。

Answer 1

下列说法错误的是:

1. String 构造函数需要读取大小 (n)。

               while ((n = zin.read(buffer, 0, 1024)) > -1) {
                   String JSON = new String(buffer, 0, n, StandardCharsets.UTF_8);
   

2. 然后，您在循环中执行最多 1024 个 JSON，而不是全部处理一个 JSON

3. UTF-8 的字节无法在某个点(例如位置 1024)进行分割，并且期望在末尾和 block 的开始处有一个有效的完整多字节序列。

4. 此外，还缺少 readFully 和 closeEntry。

简而言之:

private void getJsonContent() {
    try (ZipInputStream zin = new ZipInputStream(new BufferedInputStream(
            new FileInputStream(backupFile)))) {
        ZipEntry entry;
        while ((entry = zin.getNextEntry()) != null) {
            if (entry.getName().equalsIgnoreCase("content.json")) {
                long size = entry.getSize();
                if (size > 100_000) {
                    throw new IllegalArgumentException("Data too large");
                }
                // We could use an InputStreamReader and read text piecewise.
                // However JSON parsing also is easiest on an entire text.
                byte[] buffer = new byte[(int)size];
                int n = zin.readFully(buffer, 0, buffer.length);
                String json = new String(buffer, StandardCharsets.UTF_8);
                JSONObject obj = new JSONObject(json);
                logger.info(json);

                // Assign "global" Values to Variables
                this.createdAt = obj.getString("created_at");
                this.version = obj.getString("version");

                // Fill table if applicable                     
                for (int i = 0; i < obj.getJSONArray("content").length(); i++) {
                    JSONObject sub = obj.getJSONArray("content").getJSONObject(i);
                    logger.info(sub);

                    infoTable.addItem(new Object[] {
                            sub.get("imported_identities").toString(),
                            sub.get("project_versions").toString(),
                            sub.get("last_import").toString(),
                            sub.get("client").toString(),
                            sub.get("project").toString()
                    }, i + 1);
                }
            } // if
            zin.closeEntry(); // Do not forget preparing for the next entry
        }
    } catch (IOException e) {
        logger.info("Can't read File.");
    } catch (JSONException jse) {
        logger.info("JSON Content could not be read: " + jse.getMessage());
    }
}

即使出现异常或返回，try-with-resources 也会自动关闭。