如何将 JSON 文件读入 Java

Question

如何编写代码来读取和显示来自web_block、port_block 和user 的键和值？

我的 JSON 文件test.json:

 {
    "web_block":[
            {
                "url" : "www.facebook.com",
                "action" : "deny" 
            },
            {
                "url" : "www.google.com",
                "action" : "deny" 
            },
            {
                "url" : "www.youtube.com",
                "action" : "deny" 
            },
            {
                "url" : "www.wu.ac.th",
                "action" : "allow" 
            }
        ],
    "port_block":[
            {
                "port" : "80",
                "protocol" : "tcp",
                "action" : "block"
            },
            {
                "port" : "443",
                "protocol" : "udp",
                "action" : "allow" 
            }
        ],
       "user": [
                       {
                                "username" : "toms"
                       }
               ]

}

我尝试了以下操作：

JSONParser parser = new JSONParser();
    try {

        Object obj = parser.parse(new FileReader("d:\\test.json"));

        JSONObject jsonObject = (JSONObject) obj;

        String name = (String) jsonObject.get("web_block");
        System.out.println(url);

        long age = (Long) jsonObject.get("port_block");
        System.out.println(port);

但还是错了。

Answer 1

1. 将以下 Jackson 库添加到您的项目中 -

杰克逊数据绑定

杰克逊注解

杰克逊核心

1. 创建一个映射到您的 json 的 pojo 类 -

   public class CustomJsonData{
   
   @JsonProperty("web_block")
   private List<WebBlock> webBlock = new ArrayList<WebBlock>();
   @JsonProperty("port_block")
   private List<PortBlock> portBlock = new ArrayList<PortBlock>();
   @JsonProperty("user")
   private List<User> user = new ArrayList<User>();
   
   public CustomJsonData() {
   }
   
   public List<WebBlock> getWebBlock() {
       return webBlock;
   }
   
   public void setWebBlock(List<WebBlock> webBlock) {
       this.webBlock = webBlock;
   }
   
   public List<PortBlock> getPortBlock() {
       return portBlock;
   }
   
   public void setPortBlock(List<PortBlock> portBlock) {
       this.portBlock = portBlock;
   }
   
   public List<User> getUser() {
       return user;
   }
   
   public void setUser(List<User> user) {
       this.user = user;
   }
   
   }
   
   class PortBlock {
   
   @JsonProperty("port")
   private String port;
   @JsonProperty("protocol")
   private String protocol;
   @JsonProperty("action")
   private String action;
   
   public PortBlock() {
   }
   
   public String getPort() {
       return port;
   }
   
   public void setPort(String port) {
       this.port = port;
   }
   
   public String getProtocol() {
       return protocol;
   }
   
   public void setProtocol(String protocol) {
       this.protocol = protocol;
   }
   
   public String getAction() {
       return action;
   }
   
   public void setAction(String action) {
       this.action = action;
   }
   
   }
   
   class User {
   
   @JsonProperty("username")
   private String username;
   
   public User() {
   }
   
   public String getUsername() {
       return username;
   }
   
   public void setUsername(String username) {
       this.username = username;
   }
   
   }
   
   class WebBlock {
   
   @JsonProperty("url")
   private String url;
   @JsonProperty("action")
   private String action;
   
   public WebBlock() {
   }
   
   public String getUrl() {
       return url;
   }
   
   public void setUrl(String url) {
       this.url = url;
   }
   
   public String getAction() {
       return action;
   }
   
   public void setAction(String action) {
       this.action = action;
   }
   
   }
   

说明：“[ ]”下的json中的数据是一个数组，所以它是用数组列表映射的，而“{}”下的数据是一个对象，所以它是映射的具有字符串类型字段的特定类（例如：WebBlock、PortBlock 等）。

现在您可以检索如下数据 -

ObjectMapper mapper = new ObjectMapper();
CustomJsonData object = mapper.readValue(new FileReader("d:\\test.json"),CustomJsonData.class);     
String username = object.getUser().get(0).getUsername();
List<WebBlock> webBlocks = object.getWebBlock();
List<PortBlock> portBlocks = object.getPortBlock();

请参阅此处的示例 - http://wiki.fasterxml.com/JacksonInFiveMinutes