java - 我怎样才能把json放到java中的 map 上

Question

在我的项目中，我有一个像这样的 json 文件。

  [
   {
      "Task": {
         "refType": "EM TASK ",
         "reference": "73-22-49-100-104",
         "engType": "A5",
         "DMC": "V2500-A0-73-22-4900-03A-251A-C",
         "subTasks": {
            "SUBTASK0": "73-22-49-110-054-001",
            "SUBTASK1": "73-22-49-110-054-002"
         }
      }
   }
]

我想用这个 json 文件创建一个 map 。可以是这样的{refType,reference,engType,DMC,subTasks} 为此，我编写了这些代码

JSONParser parser = new JSONParser();
        int k=0;
        try {
            JSONObject json=null;
            System.out.println("Reading JSON file from Java program");
            FileReader fileReader = new FileReader("C:\\Users\\ftk1187\\Desktop\\jsonExample.json");
            JSONArray jsonArray = (JSONArray) parser.parse(fileReader);
            ArrayList<String> subtasks=new ArrayList<String>();
            for(int i=0;i<jsonArray.size();i++)
            {
                json=(JSONObject) jsonArray.get(i);
                JSONObject jsonValue = (JSONObject) json.get("Task");
                JSONObject subTasks = (JSONObject) jsonValue.get("subTasks");
                String reference = (String) jsonValue.get("reference");
                String refType = (String) jsonValue.get("refType");
                String engType = (String) jsonValue.get("engType");
                String dmc = (String) jsonValue.get("DMC");
                System.out.println("reference: " + reference);
                System.out.println("refType: " + refType);
                System.out.println("DMC: " + dmc);
                System.out.println("engType: " + engType);
                subtasks.addAll(subTasks.values());
                while(k<subtasks.size())
                {
                    System.out.println("SubTasks: "+subtasks.get(k));
                    k++;
                }
                ObjectMapper objectMapper=new ObjectMapper();
                Tasks map=objectMapper.readValue(fileReader, Tasks.class);
                System.out.println(map);
            }

class Tasks{
    private String engType;
    private String refType;
    private String reference;
    private String dmc;
    private String[] subTask;
    public String getEngType() {
        return engType;
    }
    public void setEngType(String engType) {
        this.engType=engType;
    }
    public String getRefType() {
        return refType;
    }
    public void setRefType(String RefType) {
        this.refType=RefType;
    }
    public String getReference() {
        return reference;
    }
    public void setReference(String Reference) {
        this.reference=Reference;
    }
    public String getDmc() {
        return dmc;
    }
    public void setDmc(String Dmc) {
        this.dmc=Dmc;
    }
    public String[] getSubTask() {
        return subTask;
    }
    public void setSubTask(String[] SubTask) {
        this.subTask=SubTask;
    }
    @Override
    public String toString() {
        StringBuilder sb=new StringBuilder();
        sb.append("{");
        sb.append(refType).append(",");
        sb.append(reference).append(",");
        sb.append(engType).append(",");
        sb.append(dmc).append(",");
        for(String subTask1:subTask) {
            sb.append(subTask1).append(",");
        }
        sb.append("}");
        return sb.toString();
    }
}

但这对我不起作用。它给了我这个错误

com.fasterxml.jackson.databind.exc.MismatchedInputException: No content to map due to end-of-input at [Source: (FileReader); line: 1, column: 0] at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:59) at com.fasterxml.jackson.databind.ObjectMapper._initForReading(ObjectMapper.java:4344) at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4189) at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3218) at DocFinder.doGet(DocFinder.java:89) at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1598) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Unknown Source)

我不知道我需要做什么。我想使用这些参数来创建 servlet 重定向。

Answer 1

您需要创建适合 JSON 有效负载的 POJO 类。之后，将 JSON 有效负载读取为树 - 作为 JSON Array。迭代它并将每个 Task 节点转换为 Tasks 类:

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.json.JsonMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

public class JsonApp {

    public static void main(String[] args) throws IOException {
        File jsonFile = new File("./src/main/resources/test.json");

        ObjectMapper mapper = JsonMapper.builder().build();

        List<Tasks> tasks = new ArrayList<>();
        ArrayNode array = (ArrayNode) mapper.readTree(jsonFile);
        array.forEach(item -> tasks.add(mapper.convertValue(item.get("Task"), Tasks.class)));

        System.out.println(tasks);
    }
}

class Tasks {
    private String engType;
    private String refType;
    private String reference;

    @JsonProperty("DMC")
    private String dmc;

    private Map<String, String> subTasks;

    // getters, setters, toString
}

上面的代码打印:

[Tasks{engType='A5', refType='EM TASK ', reference='73-22-49-100-104', dmc='V2500-A0-73-22-4900-03A-251A-C', subTasks={SUBTASK0=73-22-49-110-054-001, SUBTASK1=73-22-49-110-054-002}}]