Jackson第一個(gè)程序
在進(jìn)入學(xué)習(xí)jackson庫(kù)的細(xì)節(jié)之前,讓我們來(lái)看看應(yīng)用程序操作功能。在這個(gè)例子中,我們創(chuàng)建一個(gè)Student類。將創(chuàng)建一個(gè)JSON字符串學(xué)生的詳細(xì)信息,并將其反序列化到學(xué)生的對(duì)象,然后將其序列化到JSON字符串。
創(chuàng)建一個(gè)名為JacksonTester在Java類文件 C:/>Jackson_WORKSPACE.
文件: JacksonTester.java
import java.io.IOException;import org.codehaus.jackson.JsonParseException;import org.codehaus.jackson.map.JsonMappingException;import org.codehaus.jackson.map.ObjectMapper;import org.codehaus.jackson.map.SerializationConfig;public class JacksonTester { public static void main(String args[]){ ObjectMapper mapper = new ObjectMapper(); String jsonString = "{/"name/":/"Mahesh/", /"age/":21}"; //map json to student try { Student student = mapper.readValue(jsonString, Student.class); System.out.println(student); mapper.enable(SerializationConfig.Feature.INDENT_OUTPUT); jsonString = mapper.writeValueAsString(student); System.out.println(jsonString); } catch (JsonParseException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }}class Student { private String name; private int age; public Student(){} public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String toString(){ return "Student [ name: "+name+", age: "+ age+ " ]"; } }
驗(yàn)證結(jié)果
使用javac編譯如下類:
Student [ name: Mahesh, age: 21 ]{ "name" : "Mahesh", "age" : 21}
步驟 - 需要記住
以下是這里要考慮的重要步驟。
第1步:創(chuàng)建ObjectMapper對(duì)象。
創(chuàng)建ObjectMapper對(duì)象。它是一個(gè)可重復(fù)使用的對(duì)象。/
ObjectMapper mapper = new ObjectMapper();
//Object to JSON ConversionStudent student = mapper.readValue(jsonString, Student.class);
第3步:序列化對(duì)象到JSON。
使用writeValueAsString()方法來(lái)獲取對(duì)象的JSON字符串表示。
//Object to JSON Conversion jsonString = mapper.writeValueAsString(student);
Jackson樹(shù)模型
樹(shù)模型準(zhǔn)備JSON文件的內(nèi)存樹(shù)表示。 ObjectMapper構(gòu)建JsonNode節(jié)點(diǎn)樹(shù)。這是最靈活的方法。它類似于DOM解析器的XML。
從JSON創(chuàng)建樹(shù)
ObjectMapper提供一個(gè)指針樹(shù)的根節(jié)點(diǎn)在讀取JSON之后。根節(jié)點(diǎn)可用于遍歷完全樹(shù)。考慮下面的代碼片段獲得提供JSON字符串的根節(jié)點(diǎn)。
//Create an ObjectMapper instanceObjectMapper mapper = new ObjectMapper(); String jsonString = "{/"name/":/"Mahesh Kumar/", /"age/":21,/"verified/":false,/"marks/": [100,90,85]}";//create tree from JSONJsonNode rootNode = mapper.readTree(jsonString);
遍歷樹(shù)模型
使用相對(duì)路徑來(lái)根節(jié)點(diǎn)在遍歷樹(shù),并處理該數(shù)據(jù)得到的每個(gè)節(jié)點(diǎn)。考慮下面的代碼片段遍歷提供的根節(jié)點(diǎn)的樹(shù)。
JsonNode nameNode = rootNode.path("name");System.out.println("Name: "+ nameNode.getTextValue()); JsonNode marksNode = rootNode.path("marks");Iterator iterator = marksNode.getElements();
示例
創(chuàng)建一個(gè)名為JacksonTester在Java類文件目錄 C:/>Jackson_WORKSPACE.
File: JacksonTester.java
import java.io.IOException;import java.util.Iterator;import org.codehaus.jackson.JsonNode;import org.codehaus.jackson.JsonParseException;import org.codehaus.jackson.map.JsonMappingException;import org.codehaus.jackson.map.ObjectMapper;public class JacksonTester { public static void main(String args[]){ JacksonTester tester = new JacksonTester(); try { ObjectMapper mapper = new ObjectMapper(); String jsonString = "{/"name/":/"Mahesh Kumar/", /"age/":21,/"verified/":false,/"marks/": [100,90,85]}"; JsonNode rootNode = mapper.readTree(jsonString); JsonNode nameNode = rootNode.path("name"); System.out.println("Name: "+ nameNode.getTextValue()); JsonNode ageNode = rootNode.path("age"); System.out.println("Age: " + ageNode.getIntValue()); JsonNode verifiedNode = rootNode.path("verified"); System.out.println("Verified: " + (verifiedNode.getBooleanValue() ? "Yes":"No")); JsonNode marksNode = rootNode.path("marks"); Iterator<JsonNode> iterator = marksNode.getElements(); System.out.print("Marks: [ "); while (iterator.hasNext()) { JsonNode marks = iterator.next(); System.out.print(marks.getIntValue() + " "); } System.out.println("]"); } catch (JsonParseException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }}
驗(yàn)證輸出結(jié)果
使用javac編譯如下類:
Name: Mahesh KumarAge: 21Verified: NoMarks: [ 100 90 85 ]
樹(shù)到JSON轉(zhuǎn)換
在這個(gè)例子中,我們已經(jīng)使用JsonNode并將其寫入到一個(gè)JSON文件,并讀回創(chuàng)建了一棵樹(shù)。
創(chuàng)建一個(gè)名為JacksonTester在Java類文件目錄 C:/>Jackson_WORKSPACE.
File: JacksonTester.java
import java.io.File;import java.io.IOException;import java.util.Iterator;import org.codehaus.jackson.JsonNode;import org.codehaus.jackson.JsonParseException;import org.codehaus.jackson.map.JsonMappingException;import org.codehaus.jackson.map.ObjectMapper;import org.codehaus.jackson.node.ArrayNode;import org.codehaus.jackson.node.ObjectNode;public class JacksonTester { public static void main(String args[]){ JacksonTester tester = new JacksonTester(); try { ObjectMapper mapper = new ObjectMapper(); JsonNode rootNode = mapper.createObjectNode(); JsonNode marksNode = mapper.createArrayNode(); ((ArrayNode)marksNode).add(100); ((ArrayNode)marksNode).add(90); ((ArrayNode)marksNode).add(85); ((ObjectNode) rootNode).put("name", "Mahesh Kumar"); ((ObjectNode) rootNode).put("age", 21); ((ObjectNode) rootNode).put("verified", false); ((ObjectNode) rootNode).put("marks",marksNode); mapper.writeValue(new File("student.json"), rootNode); rootNode = mapper.readTree(new File("student.json")); JsonNode nameNode = rootNode.path("name"); System.out.println("Name: "+ nameNode.getTextValue()); JsonNode ageNode = rootNode.path("age"); System.out.println("Age: " + ageNode.getIntValue()); JsonNode verifiedNode = rootNode.path("verified"); System.out.println("Verified: " + (verifiedNode.getBooleanValue() ? "Yes":"No")); JsonNode marksNode1 = rootNode.path("marks"); Iterator<JsonNode> iterator = marksNode1.getElements(); System.out.print("Marks: [ "); while (iterator.hasNext()) { JsonNode marks = iterator.next(); System.out.print(marks.getIntValue() + " "); } System.out.println("]"); } catch (JsonParseException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }}
驗(yàn)證結(jié)果
使用javac編譯如下類:
Name: Mahesh Kumar
Age: 21
Verified: No
Marks: [ 100 90 85 ]
從樹(shù)到Java對(duì)象轉(zhuǎn)換
在這個(gè)例子中,我們已經(jīng)使用JsonNode并將其寫入到一個(gè)JSON文件,并回讀然后將一個(gè)Student對(duì)象其轉(zhuǎn)換為創(chuàng)建了一棵樹(shù)。
創(chuàng)建一個(gè)名為JacksonTester在Java類文件目錄 C:/>Jackson_WORKSPACE.
File: JacksonTester.java
import java.io.File;import java.io.IOException;import java.util.Arrays;import org.codehaus.jackson.JsonNode;import org.codehaus.jackson.JsonParseException;import org.codehaus.jackson.map.JsonMappingException;import org.codehaus.jackson.map.ObjectMapper;import org.codehaus.jackson.node.ArrayNode;import org.codehaus.jackson.node.ObjectNode;public class JacksonTester { public static void main(String args[]){ JacksonTester tester = new JacksonTester(); try { ObjectMapper mapper = new ObjectMapper(); JsonNode rootNode = mapper.createObjectNode(); JsonNode marksNode = mapper.createArrayNode(); ((ArrayNode)marksNode).add(100); ((ArrayNode)marksNode).add(90); ((ArrayNode)marksNode).add(85); ((ObjectNode) rootNode).put("name", "Mahesh Kumar"); ((ObjectNode) rootNode).put("age", 21); ((ObjectNode) rootNode).put("verified", false); ((ObjectNode) rootNode).put("marks",marksNode); mapper.writeValue(new File("student.json"), rootNode); rootNode = mapper.readTree(new File("student.json")); Student student = mapper.treeToValue(rootNode, Student.class); System.out.println("Name: "+ student.getName()); System.out.println("Age: " + student.getAge()); System.out.println("Verified: " + (student.isVerified() ? "Yes":"No")); System.out.println("Marks: "+Arrays.toString(student.getMarks())); } catch (JsonParseException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }}class Student { String name; int age; boolean verified; int[] marks; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public boolean isVerified() { return verified; } public void setVerified(boolean verified) { this.verified = verified; } public int[] getMarks() { return marks; } public void setMarks(int[] marks) { this.marks = marks; }}
驗(yàn)證結(jié)果
使用javac編譯如下類:
Name: Mahesh KumarAge: 21Verified: NoMarks: [ 100 90 85 ]
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