Map<String，Object>给空

Question

我在java中有一个POJO类，我试图使用HashMap<>提取json，但是我得到了null。我不知道为什么？这是我的pojo课程

public class NetworkConfiguration {

    @SerializedName("GUID")
    @Expose
    private String gUID;
    @SerializedName("Name")
    @Expose
    private String name;
    @SerializedName("Type")
    @Expose
    private String type;
    @SerializedName("WiFi")
    @Expose
    private WiFi wiFi;

    public NetworkConfiguration() {
    }
    public NetworkConfiguration(String gUID, String name, String type, WiFi wiFi) {
        super();
        this.gUID = gUID;
        this.name = name;
        this.type = type;
        this.wiFi = wiFi;
    }

    public String getGUID() {
        return gUID;
    }

    public void setGUID(String gUID) {
        this.gUID = gUID;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public WiFi getWiFi() {
        return wiFi;
    }

    public void setWiFi(WiFi wiFi) {
        this.wiFi = wiFi;
    }

}

这就是我是如何生成json的

List<NetworkConfiguration> networkConfigurations=new ArrayList<>;
     WiFi wiFi=new WiFi();
                        wiFi.setPassphrase(open_network_configuration_wifi_password_edit.getText().toString());
                        wiFi.setSecurity(spinner_open_network_configuration_wifi_security.getSelectedItem().toString());
                        wiFi.setSSID(open_network_configuration_wifi_ssid_edit.getText().toString());
                        if(open_network_configuration_wifi_autoconnect_option.isChecked())
                        {
                            wiFi.setAutoConnect(true);
                        }
                        else
                            {
                                wiFi.setAutoConnect(false);
                            }
                        Map<String,Object> openNetworkConfigurationMap= new HashMap<>();

                        networkConfigurations.add(new NetworkConfiguration(open_network_configuration_guid_edit.getText().toString(),
                                open_network_configuration_name_edit.getText().toString(),"WiFi",wiFi));
                        openNetworkConfigurationMap.put("NetworkConfigurations", networkConfigurations);
                        System.out.println(new JSONObject(openNetworkConfigurationMap));
                        System.out.println(networkConfigurations.get(0).getWiFi().getAutoConnect());

现在，我正在打印networkConfigurations类中添加的值，并且正确的值正在打印，但是当我打印json时，它会给我{"NetworkConfigurations":[null]}。提前感谢您的帮助

Answer 1

new JSONObject(map);

Map<String, String>**!**.警告:这只适用于你的是地图所以不能工作。

您可以从它的文档http://stleary.github.io/JSON-java/index.html中获得其他函数

葛森也可以用于序列化任意复杂的对象。

下面是您如何使用它：

Gson gson = new Gson(); 
String json = gson.toJson(myObject); 

Gson将自动将集合转换为JSON数组。Gson可以序列化私有字段，并自动忽略瞬态字段。

代码：

List<NetworkConfiguration> networkConfigurations=new ArrayList<>;
WiFi wiFi=new WiFi();
wiFi.setPassphrase(open_network_configuration_wifi_password_edit.getText().toString());
wiFi.setSecurity(spinner_open_network_configuration_wifi_security.getSelectedItem().toString());
wiFi.setSSID(open_network_configuration_wifi_ssid_edit.getText().toString());
if(open_network_configuration_wifi_autoconnect_option.isChecked())
       {
         wiFi.setAutoConnect(true);
       }
else
       {
         wiFi.setAutoConnect(false);
       }
Map<String,Object> openNetworkConfigurationMap= new HashMap<>();

networkConfigurations.add(new NetworkConfiguration(open_network_configuration_guid_edit.getText().toString(),
                                open_network_configuration_name_edit.getText().toString(),"WiFi",wiFi));
openNetworkConfigurationMap.put("NetworkConfigurations", networkConfigurations);
Gson gson = new Gson();
String json = gson.toJson(openNetworkConfigurationMap);
System.out.println(json);
System.out.println(networkConfigurations.get(0).getWiFi().getAutoConnect());

此外，确保Gson库在您的构建路径中。如果是maven，可以将以下依赖项添加到pom文件中

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.6</version>
</dependency>

如果您正在使用任何其他构建包(因为您在任何地方都没有提到)，请执行适当的步骤来实现GSON。