12

I'm a spring newbie. Wrote really simple code to get an array of JSON object from the API call at http://api.engin.umich.edu/hostinfo/...PONT&room=B505

Only get "Name: NULL"

import org.springframework.web.client.RestTemplate;

public class Application {
    public static void main(String args[]) {
        RestTemplate restTemplate = new RestTemplate();
        Computer[] computer = restTemplate.getForObject("http://api.engin.umich.edu/hostinfo/v1/computers.json?building=PIERPONT&room=B505", Computer[].class);
        System.out.println("Name:    " + computer[0].getName());
    }
}

Here goes the simple computer class.

package hello;
import org.codehaus.jackson.annotate.JsonIgnoreProperties;

@JsonIgnoreProperties(ignoreUnknown = true)
public class Computer {
    private String hostname;

    public String getName() {
        return hostname;
    }

    public String toString() {
        return "Computer [hostname=" + hostname + "]";
    }
}
maxteneff
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Ben
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  • We need more code, for instance your computer model. But off hand you are probably mapping it incorrectly, the JSON doesn't have a name, it has a hostname. – digitaljoel Oct 31 '13 at 03:00
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    http://api.engin.umich.edu/hostinfo/v1/computers.json?building=PIERPONT&room=B505 – Ben Oct 31 '13 at 03:32
  • If go to the link above, there is an attribute called hostname. – Ben Oct 31 '13 at 03:33

1 Answers1

33

Tested and working!

Some observations:

  • If you don't know so much about Spring framework, it doesn't matter. To serialize/deserialize JSON can be done in many ways.

  • I have looked that your JSON contains some reserved words like class or string. In order to handle this you will need to use @JsonProperty annotation (you will see it later at Computer.java and others). I also used this annotation for not declaring some variables that in your JSON properties contain underscores (remember that your DTO's [beans] must have the same structure, datatypes and also use the same JSON property names).

  • To resolve the problem regarding your RestTemplate object (I am not sure if you are doing it the right way when using Computer[].class). As a recommendation, please consider following/checking this code snippet: https://stackoverflow.com/a/6349488/1178686

  • This is just personal: If you consider this answer fits you requirement, don't forget to click the check next to the answer to select it, I am just typing this because you are new here, no offense.

Code:

  • I have implemented four classes, three of them as DTO's [beans]: Computer.java, Load.java, Location.java and a test class: JSONParse.java. Please review the code!

Computer.java

package com.example.dto;

import java.util.List;
import javax.xml.bind.annotation.XmlRootElement;
import org.codehaus.jackson.annotate.JsonProperty;

@XmlRootElement
public class Computer {

    private String hostname;
    private String vendor;
    private String model;
    private int swap;
    private int memory;
    @JsonProperty("sess_count")
    private int sessCount;
    private List<Load> load;
    @JsonProperty("in_use")
    private boolean inUse;
    @JsonProperty("free_in_tmp")
    private int freeInTmp;
    @JsonProperty("class")
    private String clazz;
    private List<Location> location;
    @JsonProperty("last_access")
    private String lastAccess;
    @JsonProperty("last_report")
    private int lastReport;
    private String ip;

    public String getHostname() {
        return hostname;
    }

    public void setHostname(String hostname) {
        this.hostname = hostname;
    }

    public String getVendor() {
        return vendor;
    }

    public void setVendor(String vendor) {
        this.vendor = vendor;
    }

    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    public int getSwap() {
        return swap;
    }

    public void setSwap(int swap) {
        this.swap = swap;
    }

    public int getMemory() {
        return memory;
    }

    public void setMemory(int memory) {
        this.memory = memory;
    }

    public int getSessCount() {
        return sessCount;
    }

    public void setSessCount(int sessCount) {
        this.sessCount = sessCount;
    }

    public List<Load> getLoad() {
        return load;
    }

    public void setLoad(List<Load> load) {
        this.load = load;
    }

    public boolean isInUse() {
        return inUse;
    }

    public void setInUse(boolean inUse) {
        this.inUse = inUse;
    }

    public int getFreeInTmp() {
        return freeInTmp;
    }

    public void setFreeInTmp(int freeInTmp) {
        this.freeInTmp = freeInTmp;
    }

    public String getClazz() {
        return clazz;
    }

    public void setClazz(String clazz) {
        this.clazz = clazz;
    }

    public List<Location> getLocation() {
        return location;
    }

    public void setLocation(List<Location> location) {
        this.location = location;
    }

    public String getLastAccess() {
        return lastAccess;
    }

    public void setLastAccess(String lastAccess) {
        this.lastAccess = lastAccess;
    }

    public int getLastReport() {
        return lastReport;
    }

    public void setLastReport(int lastReport) {
        this.lastReport = lastReport;
    }

    public String getIp() {
        return ip;
    }

    public void setIp(String ip) {
        this.ip = ip;
    }

    @Override
    public String toString() {
        String str = "=================================\r\n";
        str += "Hostname: " + hostname + "\r\n" +
                "Vendor: " + vendor + "\r\n" + 
                "Model: " + model + "\r\n" +
                "Swap: " + swap + "\r\n" +
                "Memory: " + memory + "\r\n" +
                "Sess_Count: " + sessCount + "\r\n" +
                "Load: " + "\r\n";

        for(Load ld : load) {
            str += "\t" + "One: " + ld.getOne() + "\r\n";
            str += "\t" + "Five: " + ld.getFive() + "\r\n";
            str += "\t" + "Fifteen: " + ld.getFifteen() + "\r\n";
        }

        str += "In_Use: " + inUse + "\r\n" +
                "Free_In_Tmp: " + freeInTmp + "\r\n" +
                "Class: " + clazz + "\r\n" +
                "Location: " + "\r\n";

        for(Location lc : location) {
            str += "\t" + "Building: " + lc.getBuilding() + "\r\n";
            str += "\t" + "Computers: " + lc.getComputers() + "\r\n";
            str += "\t" + "Room: " + lc.getRoom() + "\r\n";
            str += "\t" + "String: " + lc.getStr() + "\r\n";
        }

        str += "Ip: " + ip + "\r\n";
        str += "Last_Access: " + lastAccess + "\r\n";
        str += "Last_Report: " + lastReport + "\r\n";

        return str;     
    }
}

Load.java

package com.example.dto;

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Load {

    private int one;
    private int five;
    private int fifteen;

    public int getOne() {
        return one;
    }

    public void setOne(int one) {
        this.one = one;
    }

    public int getFive() {
        return five;
    }

    public void setFive(int five) {
        this.five = five;
    }

    public int getFifteen() {
        return fifteen;
    }

    public void setFifteen(int fifteen) {
        this.fifteen = fifteen;
    }

}

Location.java

package com.example.dto;

import javax.xml.bind.annotation.XmlRootElement;

import org.codehaus.jackson.annotate.JsonProperty;

@XmlRootElement
public class Location {

    private String room;
    private String building;
    private String computers;
    @JsonProperty("string")
    private String str;

    public String getRoom() {
        return room;
    }

    public void setRoom(String room) {
        this.room = room;
    }

    public String getBuilding() {
        return building;
    }

    public void setBuilding(String building) {
        this.building = building;
    }

    public String getComputers() {
        return computers;
    }

    public void setComputers(String computers) {
        this.computers = computers;
    }

    public String getStr() {
        return str;
    }

    public void setStr(String str) {
        this.str = str;
    }

}

JSONParse.java: runnable class just for testing purposes.

package com.example.main;

import java.io.IOException;
import java.net.URL;
import java.util.List;

import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.DeserializationConfig.Feature;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.type.TypeReference;

import com.example.dto.Computer;

public class JSONParse {

    public static void main(String args[]) throws JsonParseException, JsonMappingException, IOException {

        /* JSON provider */
        URL url = new URL("http://api.engin.umich.edu/hostinfo/v1/computers.json?building=PIERPONT&room=B505");

        ObjectMapper mapper = new ObjectMapper();

        /*
         * This allows the ObjectMapper to accept single values for a collection.
         * For example: "location" property in the returned JSON is a collection that 
         * can accept multiple objects but, in deserialization process, this property just 
         * have one object and causes an Exception.
         */
        mapper.configure(Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);

        /* 
         * If some JSON property is not present, avoid exceptions setting
         * FAIL_ON_UNKNOWN_PROPERTIES to false 
         */
        mapper.configure(Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);

        /* Get all computers */
        List<Computer> computers = mapper.readValue(url, new TypeReference<List<Computer>>(){});

        /* Print each computer (previously overriding "toString()" method) */
        for(Computer computer : computers) {
            System.out.println(computer.toString());
        }

    }

}

Output from the above class:

=================================
Hostname: pierb505p13.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 0
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9608460
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.23
Last_Access: 
Last_Report: 1383202078

=================================
Hostname: pierb505p22.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 0
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9609244
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.32
Last_Access: 
Last_Report: 1383201987

=================================
Hostname: pierb505p06.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 0
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9606464
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.16
Last_Access: 
Last_Report: 1383201982

=================================
Hostname: pierb505p17.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 0
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9606820
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.27
Last_Access: 
Last_Report: 1383202064

=================================
Hostname: pierb505p15.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 0
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9609052
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.25
Last_Access: 
Last_Report: 1383202052

=================================
Hostname: pierb505p12.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 0
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9607136
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.22
Last_Access: 
Last_Report: 1383202037

=================================
Hostname: pierb505p03.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 0
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9603132
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.13
Last_Access: 
Last_Report: 1383201964

=================================
Hostname: pierb505p14.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 0
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9599592
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.24
Last_Access: 
Last_Report: 1383201996

=================================
Hostname: pierb505p07.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 0
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9608176
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.17
Last_Access: 
Last_Report: 1383202127

=================================
Hostname: pierb505p23.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 1
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9600968
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.33
Last_Access: 
Last_Report: 1383202013

=================================
Hostname: pierb505p11.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 1
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9607224
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.21
Last_Access: 
Last_Report: 1383202098

=================================
Hostname: pierb505p21.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 1
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9595136
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.31
Last_Access: 
Last_Report: 1383202035

=================================
Hostname: pierb505p16.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 1
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9601212
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.26
Last_Access: 
Last_Report: 1383202106

=================================
Hostname: pierb505p04.engin.umich.edu
Vendor: Linux
Model: Dell 980
Swap: 8126456
Memory: 7797
Sess_Count: 0
Load: 
  One: 1
  Five: 0
  Fifteen: 0
In_Use: false
Free_In_Tmp: 9603220
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.14
Last_Access: 
Last_Report: 1383202135

=================================
Hostname: pierb505p08.engin.umich.edu
Vendor: Windows
Model: OptiPlex 980
Swap: 0
Memory: 0
Sess_Count: 0
Load: 
  One: 1
  Five: 5
  Fifteen: 15
In_Use: false
Free_In_Tmp: 16024588
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.18
Last_Access: 
Last_Report: 1383202133

=================================
Hostname: pierb505p25.engin.umich.edu
Vendor: Windows
Model: OptiPlex 980
Swap: 0
Memory: 0
Sess_Count: 0
Load: 
  One: 1
  Five: 5
  Fifteen: 15
In_Use: false
Free_In_Tmp: 10299356
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.35
Last_Access: 
Last_Report: 1383202100

=================================
Hostname: pierb505p26.engin.umich.edu
Vendor: Windows
Model: OptiPlex 980
Swap: 0
Memory: 0
Sess_Count: 0
Load: 
  One: 1
  Five: 5
  Fifteen: 15
In_Use: false
Free_In_Tmp: 11303888
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.36
Last_Access: 
Last_Report: 1383202027

=================================
Hostname: pierb505p19.engin.umich.edu
Vendor: Windows
Model: OptiPlex 980
Swap: 0
Memory: 0
Sess_Count: 0
Load: 
  One: 1
  Five: 5
  Fifteen: 15
In_Use: false
Free_In_Tmp: 15914176
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.29
Last_Access: 
Last_Report: 1383202081

=================================
Hostname: pierb505p09.engin.umich.edu
Vendor: Windows
Model: OptiPlex 980
Swap: 0
Memory: 0
Sess_Count: 0
Load: 
  One: 1
  Five: 5
  Fifteen: 15
In_Use: false
Free_In_Tmp: 29956064
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.19
Last_Access: 
Last_Report: 1383201997

=================================
Hostname: pierb505p10.engin.umich.edu
Vendor: Windows
Model: OptiPlex 980
Swap: 0
Memory: 0
Sess_Count: 0
Load: 
  One: 1
  Five: 5
  Fifteen: 15
In_Use: false
Free_In_Tmp: 19663960
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.20
Last_Access: 
Last_Report: 1383202003

=================================
Hostname: pierb505p24.engin.umich.edu
Vendor: Windows
Model: OptiPlex 980
Swap: 0
Memory: 0
Sess_Count: 0
Load: 
  One: 1
  Five: 5
  Fifteen: 15
In_Use: false
Free_In_Tmp: 19197988
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.34
Last_Access: 
Last_Report: 1383202038

=================================
Hostname: pierb505p20.engin.umich.edu
Vendor: Windows
Model: OptiPlex 980
Swap: 0
Memory: 0
Sess_Count: 0
Load: 
  One: 1
  Five: 5
  Fifteen: 15
In_Use: false
Free_In_Tmp: 9585536
Class: L
Location: 
  Building: PIERPONT
  Computers: 26
  Room: B505
  String: B505 PIERPONT
Ip: 141.213.54.30
Last_Access: 
Last_Report: 1383201994

Enjoy!

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