欢迎来到 Java JSON 示例教程. ** JSON** (JavaScript Object Notation) 是基于文本的轻量级技术,用于生成人体可读的格式化数据. JSON 代表对象数据以关键值对的形式。
Java JSON 编辑
JSON is widely used in web applications or as server response because it's lightweight and more compact than XML. JSON objects are easy to read and write and most of the technologies provide support for JSON objects. That's why JSON in Java web services are very popular. JSR353 finally made into Java EE 7 and it's the Java JSON processing API. jsonp is the reference implementation for Java JSON Processing API. We can use this in maven project by adding following dependency.
1<dependency>
2 <groupId>org.glassfish</groupId>
3 <artifactId>javax.json</artifactId>
4 <version>1.0.2</version>
5</dependency>
如果您正在使用 GlassFish 4.0,那么您可以按提供的方式保持范围,因为它已经包含在服务器中。
- 对象模型 API - 类似于 DOM Parser并且适用于小型对象
- 流式 API - 类似于 StaX Parser并且适用于不希望存储整个对象的大型对象
Java JSON API 的一些重要界面是:
我们可以从Json类或JsonReaderFactory 2. javax.json.JsonWriter:我们可以使用这个来读JSON对象到输出流 3. **javax.json.stream_3. javax.json.stream_5.json.stream_5.json.JsonParser: 这是一个引导分析器和提供流媒体支持读JSON对象 4. javax.json.stream.JsonGenerator:我们可以使用这个来写JSON对象到输出流( _3)。 javax.json.stream_5.jsonParser:这是制作JSON处理对象的工厂类。
让我们来看看使用Java JSON API的简单程序,我们有一个JSON对象存储在 employee.txt文件中。
1{
2 "id":123,
3 "name":"Pankaj Kumar",
4 "permanent":true,
5 "address":{
6 "street":"El Camino Real",
7 "city":"San Jose",
8 "zipcode":95014
9 },
10 "phoneNumbers":[9988664422, 1234567890],
11 "role":"Developer"
12}
我们有 java bean 类,代表 JSON 格式如下:
1package com.journaldev.model;
2
3import java.util.Arrays;
4
5public class Employee {
6
7 private int id;
8 private String name;
9 private boolean permanent;
10 private Address address;
11 private long[] phoneNumbers;
12 private String role;
13
14 public int getId() {
15 return id;
16 }
17 public void setId(int id) {
18 this.id = id;
19 }
20 public String getName() {
21 return name;
22 }
23 public void setName(String name) {
24 this.name = name;
25 }
26 public boolean isPermanent() {
27 return permanent;
28 }
29 public void setPermanent(boolean permanent) {
30 this.permanent = permanent;
31 }
32 public Address getAddress() {
33 return address;
34 }
35 public void setAddress(Address address) {
36 this.address = address;
37 }
38 public long[] getPhoneNumbers() {
39 return phoneNumbers;
40 }
41 public void setPhoneNumbers(long[] phoneNumbers) {
42 this.phoneNumbers = phoneNumbers;
43 }
44 public String getRole() {
45 return role;
46 }
47 public void setRole(String role) {
48 this.role = role;
49 }
50
51 @Override
52 public String toString(){
53 StringBuilder sb = new StringBuilder();
54 sb.append("***** Employee Details *****\n");
55 sb.append("ID="+getId()+"\n");
56 sb.append("Name="+getName()+"\n");
57 sb.append("Permanent="+isPermanent()+"\n");
58 sb.append("Role="+getRole()+"\n");
59 sb.append("Phone Numbers="+Arrays.toString(getPhoneNumbers())+"\n");
60 sb.append("Address="+getAddress());
61 sb.append("\n*****************************");
62
63 return sb.toString();
64 }
65}
1package com.journaldev.model;
2
3public class Address {
4
5 private String street;
6 private String city;
7 private int zipcode;
8
9 public String getStreet() {
10 return street;
11 }
12 public void setStreet(String street) {
13 this.street = street;
14 }
15 public String getCity() {
16 return city;
17 }
18 public void setCity(String city) {
19 this.city = city;
20 }
21 public int getZipcode() {
22 return zipcode;
23 }
24 public void setZipcode(int zipcode) {
25 this.zipcode = zipcode;
26 }
27
28 @Override
29 public String toString(){
30 return getStreet() + ", "+getCity()+", "+getZipcode();
31 }
32}
我已经翻译了 toString() 方法,以返回我们将在 JSON 实现类中使用的可读 String 表示。
Java JSON 阅读示例
1package com.journaldev.json;
2
3import java.io.FileInputStream;
4import java.io.IOException;
5import java.io.InputStream;
6
7import javax.json.Json;
8import javax.json.JsonArray;
9import javax.json.JsonObject;
10import javax.json.JsonReader;
11import javax.json.JsonValue;
12
13import com.journaldev.model.Address;
14import com.journaldev.model.Employee;
15
16public class EmployeeJSONReader {
17
18 public static final String JSON_FILE="employee.txt";
19
20 public static void main(String[] args) throws IOException {
21 InputStream fis = new FileInputStream(JSON_FILE);
22
23 //create JsonReader object
24 JsonReader jsonReader = Json.createReader(fis);
25
26 /**
27 * We can create JsonReader from Factory also
28 JsonReaderFactory factory = Json.createReaderFactory(null);
29 jsonReader = factory.createReader(fis);
30 */
31
32 //get JsonObject from JsonReader
33 JsonObject jsonObject = jsonReader.readObject();
34
35 //we can close IO resource and JsonReader now
36 jsonReader.close();
37 fis.close();
38
39 //Retrieve data from JsonObject and create Employee bean
40 Employee emp = new Employee();
41
42 emp.setId(jsonObject.getInt("id"));
43 emp.setName(jsonObject.getString("name"));
44 emp.setPermanent(jsonObject.getBoolean("permanent"));
45 emp.setRole(jsonObject.getString("role"));
46
47 //reading arrays from json
48 JsonArray jsonArray = jsonObject.getJsonArray("phoneNumbers");
49 long[] numbers = new long[jsonArray.size()];
50 int index = 0;
51 for(JsonValue value : jsonArray){
52 numbers[index++] = Long.parseLong(value.toString());
53 }
54 emp.setPhoneNumbers(numbers);
55
56 //reading inner object from json object
57 JsonObject innerJsonObject = jsonObject.getJsonObject("address");
58 Address address = new Address();
59 address.setStreet(innerJsonObject.getString("street"));
60 address.setCity(innerJsonObject.getString("city"));
61 address.setZipcode(innerJsonObject.getInt("zipcode"));
62 emp.setAddress(address);
63
64 //print employee bean information
65 System.out.println(emp);
66
67 }
68
69}
JsonReaderFactory 实现了 Factory Design Pattern。
1***** Employee Details *****
2ID=123
3Name=Pankaj Kumar
4Permanent=true
5Role=Developer
6Phone Numbers=[9988664422, 1234567890]
7Address=El Camino Real, San Jose, 95014
8*****************************
Java JSON 写作示例
1package com.journaldev.json;
2
3import java.io.FileNotFoundException;
4import java.io.FileOutputStream;
5import java.io.OutputStream;
6
7import javax.json.Json;
8import javax.json.JsonArrayBuilder;
9import javax.json.JsonObject;
10import javax.json.JsonObjectBuilder;
11import javax.json.JsonWriter;
12
13import com.journaldev.model.Address;
14import com.journaldev.model.Employee;
15
16public class EmployeeJSONWriter {
17
18 public static void main(String[] args) throws FileNotFoundException {
19
20 Employee emp = createEmployee();
21
22 JsonObjectBuilder empBuilder = Json.createObjectBuilder();
23 JsonObjectBuilder addressBuilder = Json.createObjectBuilder();
24 JsonArrayBuilder phoneNumBuilder = Json.createArrayBuilder();
25
26 for (long phone : emp.getPhoneNumbers()) {
27 phoneNumBuilder.add(phone);
28 }
29
30 addressBuilder.add("street", emp.getAddress().getStreet())
31 .add("city", emp.getAddress().getCity())
32 .add("zipcode", emp.getAddress().getZipcode());
33
34 empBuilder.add("id", emp.getId())
35 .add("name", emp.getName())
36 .add("permanent", emp.isPermanent())
37 .add("role", emp.getRole());
38
39 empBuilder.add("phoneNumbers", phoneNumBuilder);
40 empBuilder.add("address", addressBuilder);
41
42 JsonObject empJsonObject = empBuilder.build();
43
44 System.out.println("Employee JSON String\n"+empJsonObject);
45
46 //write to file
47 OutputStream os = new FileOutputStream("emp.txt");
48 JsonWriter jsonWriter = Json.createWriter(os);
49 /**
50 * We can get JsonWriter from JsonWriterFactory also
51 JsonWriterFactory factory = Json.createWriterFactory(null);
52 jsonWriter = factory.createWriter(os);
53 */
54 jsonWriter.writeObject(empJsonObject);
55 jsonWriter.close();
56 }
57
58
59 public static Employee createEmployee() {
60
61 Employee emp = new Employee();
62 emp.setId(100);
63 emp.setName("David");
64 emp.setPermanent(false);
65 emp.setPhoneNumbers(new long[] { 123456, 987654 });
66 emp.setRole("Manager");
67
68 Address add = new Address();
69 add.setCity("Bangalore");
70 add.setStreet("BTM 1st Stage");
71 add.setZipcode(560100);
72 emp.setAddress(add);
73
74 return emp;
75 }
76
77}
一旦我们运行上面的应用程序,我们得到以下响应:
1Employee JSON String
2{"id":100,"name":"David","permanent":false,"role":"Manager","phoneNumbers":[123456,987654],"address":{"street":"BTM 1st Stage","city":"Bangalore","zipcode":560100}}
JsonObjectBuilder 实现了 builder pattern,使其非常易于使用。
Java JSON 参数示例
Java JsonParser 是一个拖解解析器,我们用 next() 方法读取下一个元素,该元素返回了事件对象。 javax.json.stream.JsonParser.Event 是一个 (Enum)(/community/tutorials/java-enum),使其是安全的和易于使用的元素。
1package com.journaldev.json;
2
3import java.io.FileInputStream;
4import java.io.IOException;
5import java.io.InputStream;
6import java.util.ArrayList;
7import java.util.List;
8
9import javax.json.Json;
10import javax.json.stream.JsonParser;
11import javax.json.stream.JsonParser.Event;
12
13import com.journaldev.model.Address;
14import com.journaldev.model.Employee;
15
16public class EmployeeJSONParser {
17
18 public static final String FILE_NAME = "employee.txt";
19
20 public static void main(String[] args) throws IOException {
21 InputStream fis = new FileInputStream(FILE_NAME);
22
23 JsonParser jsonParser = Json.createParser(fis);
24
25 /**
26 * We can create JsonParser from JsonParserFactory also with below code
27 * JsonParserFactory factory = Json.createParserFactory(null);
28 * jsonParser = factory.createParser(fis);
29 */
30
31 Employee emp = new Employee();
32 Address address = new Address();
33 String keyName = null;
34 List<Long> phoneNums = new ArrayList<Long>();
35
36 while (jsonParser.hasNext()) {
37 Event event = jsonParser.next();
38 switch (event) {
39 case KEY_NAME:
40 keyName = jsonParser.getString();
41 break;
42 case VALUE_STRING:
43 setStringValues(emp, address, keyName, jsonParser.getString());
44 break;
45 case VALUE_NUMBER:
46 setNumberValues(emp, address, keyName, jsonParser.getLong(), phoneNums);
47 break;
48 case VALUE_FALSE:
49 setBooleanValues(emp, address, keyName, false);
50 break;
51 case VALUE_TRUE:
52 setBooleanValues(emp, address, keyName, true);
53 break;
54 case VALUE_NULL:
55 // don't set anything
56 break;
57 default:
58 // we are not looking for other events
59 }
60 }
61 emp.setAddress(address);
62 long[] nums = new long[phoneNums.size()];
63 int index = 0;
64 for(Long l :phoneNums){
65 nums[index++] = l;
66 }
67 emp.setPhoneNumbers(nums);
68
69 System.out.println(emp);
70
71 //close resources
72 fis.close();
73 jsonParser.close();
74 }
75
76 private static void setNumberValues(Employee emp, Address address,
77 String keyName, long value, List<Long> phoneNums) {
78 switch(keyName){
79 case "zipcode":
80 address.setZipcode((int)value);
81 break;
82 case "id":
83 emp.setId((int) value);
84 break;
85 case "phoneNumbers":
86 phoneNums.add(value);
87 break;
88 default:
89 System.out.println("Unknown element with key="+keyName);
90 }
91 }
92
93 private static void setBooleanValues(Employee emp, Address address,
94 String key, boolean value) {
95 if("permanent".equals(key)){
96 emp.setPermanent(value);
97 }else{
98 System.out.println("Unknown element with key="+key);
99 }
100 }
101
102 private static void setStringValues(Employee emp, Address address,
103 String key, String value) {
104 switch(key){
105 case "name":
106 emp.setName(value);
107 break;
108 case "role":
109 emp.setRole(value);
110 break;
111 case "city":
112 address.setCity(value);
113 break;
114 case "street":
115 address.setStreet(value);
116 break;
117 default:
118 System.out.println("Unknown Key="+key);
119
120 }
121 }
122
123}
主要的复杂性是当我们需要写逻辑来分析数据时,有时它可以变得复杂. 由于我们正在阅读与JsonReader相同的文件,输出与EmployeeJsonReader程序相同。
Java JsonGenerator 例子
1package com.journaldev.json;
2
3import java.io.FileOutputStream;
4import java.io.IOException;
5import java.io.OutputStream;
6
7import javax.json.Json;
8import javax.json.stream.JsonGenerator;
9
10import com.journaldev.model.Employee;
11
12public class EmployeeJSONGenerator {
13
14 public static void main(String[] args) throws IOException {
15 OutputStream fos = new FileOutputStream("emp_stream.txt");
16 JsonGenerator jsonGenerator = Json.createGenerator(fos);
17 /**
18 * We can get JsonGenerator from Factory class also
19 * JsonGeneratorFactory factory = Json.createGeneratorFactory(null);
20 * jsonGenerator = factory.createGenerator(fos);
21 */
22
23 Employee emp = EmployeeJSONWriter.createEmployee();
24 jsonGenerator.writeStartObject(); // {
25 jsonGenerator.write("id", emp.getId()); // "id":123
26 jsonGenerator.write("name", emp.getName());
27 jsonGenerator.write("role", emp.getRole());
28 jsonGenerator.write("permanent", emp.isPermanent());
29
30 jsonGenerator.writeStartObject("address") //start of address object
31 .write("street", emp.getAddress().getStreet())
32 .write("city",emp.getAddress().getCity())
33 .write("zipcode",emp.getAddress().getZipcode())
34 .writeEnd(); //end of address object
35
36 jsonGenerator.writeStartArray("phoneNumbers"); //start of phone num array
37 for(long num : emp.getPhoneNumbers()){
38 jsonGenerator.write(num);
39 }
40 jsonGenerator.writeEnd(); // end of phone num array
41 jsonGenerator.writeEnd(); // }
42
43 jsonGenerator.close();
44
45 }
46
47}
JsonGenerator 非常易于使用,为大数据提供良好的性能,这对于 Java JSON 处理 API 来说都是如此。我们了解了 Java JSON Parser、阅读和写作示例,您可以从下面的链接下载 Java 项目并玩它。
(下载Java JSON项目)
参考: JSONLint - 验证 JSON 数据的伟大 Web 工具 JSON 处理参考实施 JSR353 JCP 页面