Jackson2.x的使用

快来打我* 2022-05-21 00:24 213阅读 0赞

**Jackson fastxml和codehaus的区别**

他们是jackson的2大分支，从2.0更名为fastxml.jackson，json是web应用之间传输的公认标准

**Jackson fastxml的结构**

** **   jackson-core 核心包

jackson-annotations 注解包

jackson-databind 数据绑定 依赖core和annotation

**使用方式，提供了三种json处理方式**

*  Streaming API : 其他两种方式都依赖于它而实现，如果要从底层细粒度控制 json 的解析生成，可以使用这种方式;
 *  Tree Model : 通过基于内存的树形结构来描述 json 数据。json 结构树由 JsonNode 组成。不需要绑定任何类和实体，可以方便的对 JsonNode 来进行操作。
 *  Data Binding : 最常用的方式，基于属性的 get 和 set方法以及注解来实现 JavaBean 和 json 的互转，底层实现还是 Streaming API.

#### 代码示例 ####

`Streaming API`示例

package com.maolv.oschina; import java.util.ArrayList; import java.util.List; import org.junit.After; import org.junit.Before; import org.junit.Test; import com.fasterxml.jackson.core.JsonFactory; import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.core.JsonParser; import com.fasterxml.jackson.core.JsonToken; /** * Jackson 流处理APi处理 */ public class JacksonStreamAPITest { private JsonFactory factory; private JsonGenerator jsonGenerator; @Before public void init() throws Exception { factory = new JsonFactory(); // 工厂全局设置 factory.disable(JsonFactory.Feature.CANONICALIZE_FIELD_NAMES); // 设置解析器 factory.enable(JsonParser.Feature.ALLOW_SINGLE_QUOTES); // 设置生成器 factory.enable(JsonGenerator.Feature.WRITE_NUMBERS_AS_STRINGS); // 设置输出到console jsonGenerator = factory.createGenerator(System.out); // 覆盖上面的设置 jsonGenerator.disable(JsonGenerator.Feature.WRITE_NUMBERS_AS_STRINGS); } @Test public void testGenerator() throws Exception { String str = "hello,world!jackson!"; // 输出字节 jsonGenerator.writeBinary(str.getBytes()); // 输出布尔型 jsonGenerator.writeBoolean(true); // null jsonGenerator.writeNull(); // 输出字符型 jsonGenerator.writeNumber(2.2f); // 使用Raw方法会执行字符中的特殊字符 jsonGenerator.writeRaw("\tc"); // 输出换行符 jsonGenerator.writeRaw("\r\n"); // 构造Json数据 jsonGenerator.writeStartObject(); jsonGenerator.writeStringField("message", "Hello World!"); jsonGenerator.writeArrayFieldStart("names"); jsonGenerator.writeString("周杰伦"); jsonGenerator.writeString("王力宏"); jsonGenerator.writeEndArray(); jsonGenerator.writeEndObject(); } @Test public void testParser() throws Exception { String testStr = "{\"message\":\"Hello World!\",\"names\":[\"周杰伦\",\"王力宏\"]}"; JsonParser p = factory.createParser(testStr); JsonToken t = p.nextToken(); List<String> names = new ArrayList<String>(); if ( t != JsonToken.START_OBJECT){ System.out.println("Json格式不正确!"); } while (t != JsonToken.END_OBJECT){ if (t == JsonToken.FIELD_NAME && "message".equals(p.getCurrentName())){ t = p.nextToken(); String message = p.getText(); System.out.printf("My message to you is %s!\n", message); } if (t == JsonToken.FIELD_NAME && "names".equals(p.getCurrentName())){ t = p.nextToken(); while (t != JsonToken.END_ARRAY){ if (t == JsonToken.VALUE_STRING){ String name = p.getValueAsString(); names.add(name); } t = p.nextToken(); } } t = p.nextToken(); } System.out.println(names.toString()); p.close(); } @After public void close() throws Exception { jsonGenerator.close(); } }

运行结果

"aGVsbG8sd29ybGQhamFja3NvbiE=" true null 2.2    c
    {"message":"Hello World!","names":["周杰伦","王力宏"]}

Tree Model

package com.maolv.oschina; import org.junit.Before; import org.junit.Test; import com.fasterxml.jackson.annotation.JsonInclude; import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.core.JsonParser; import com.fasterxml.jackson.databind.DeserializationFeature; import com.fasterxml.jackson.databind.JsonNode; import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.SerializationFeature; import com.fasterxml.jackson.databind.node.ArrayNode; import com.fasterxml.jackson.databind.node.JsonNodeFactory; import com.fasterxml.jackson.databind.node.ObjectNode; /** * Jackson Tree Model解析生成示例 */ public class JacksonTreeModelTest { private ObjectMapper objectMapper; @Before public void init() { objectMapper = new ObjectMapper(); // 如果为空则不输出 objectMapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY); // 对于空的对象转json的时候不抛出错误 objectMapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS); // 禁用序列化日期为timestamps objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS); // 禁用遇到未知属性抛出异常 objectMapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES); // 视空字符传为null objectMapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT); // 低层级配置 objectMapper.configure(JsonParser.Feature.ALLOW_COMMENTS, true); // 允许属性名称没有引号 objectMapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true); // 允许单引号 objectMapper.configure(JsonParser.Feature.ALLOW_SINGLE_QUOTES, true); // 取消对非ASCII字符的转码 objectMapper.configure(JsonGenerator.Feature.ESCAPE_NON_ASCII, false); } @Test public void testTreeModel() throws Exception { JsonNodeFactory nodeFactory = objectMapper.getNodeFactory(); // 创建一个model ObjectNode node = nodeFactory.objectNode(); node.put("age", 18); // 新增 node.put("name", "周杰伦"); // 如果存在同名的则是替换操作 node.put("age", 19); ArrayNode coursesNode = node.putArray("courses"); coursesNode.add("思想政治"); coursesNode.add("高等数学"); // 获取节点类型 System.out.println(node.getNodeType()); System.out.println(coursesNode.getNodeType()); // 移除第一个 coursesNode.remove(0); // 输出 System.out.println(node.toString()); String jsonStr = "{\"age\":19,\"name\":\"周杰伦\",\"courses\":[\"高等数学\"]}"; JsonNode jsonNode = objectMapper.readTree(jsonStr); ArrayNode arrayNode = (ArrayNode) jsonNode.withArray("courses"); arrayNode.add("马列"); for (int i = 0;i < arrayNode.size();i++){ System.out.println(arrayNode.get(i).asText()); } System.out.println(jsonNode.toString()); } }

运行结果:

OBJECT
    ARRAY
    {"age":19,"name":"周杰伦","courses":["高等数学"]}
    高等数学
    马列
    {"age":19,"name":"周杰伦","courses":["高等数学","马列"]}

`Data Binding` 示例

package com.maolv.oschina; import java.io.IOException; import java.text.SimpleDateFormat; import java.util.Date; import org.junit.Before; import org.junit.Test; import com.fasterxml.jackson.annotation.JsonInclude; import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.core.JsonParser; import com.fasterxml.jackson.databind.DeserializationFeature; import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.SerializationFeature; /** * Jackson Data bind 解析生成示例 */ public class JacksonDataBindTest { private ObjectMapper baseMapper; private ObjectMapper prettyMapper1; private ObjectMapper prettyMapper2; private ObjectMapper nonEmptyMapper; @Before public void init(){ baseMapper = new ObjectMapper(); // 对于空的对象转json的时候不抛出错误 baseMapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS); // 禁用遇到未知属性抛出异常 baseMapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES); baseMapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT); // 低层级配置 baseMapper.configure(JsonParser.Feature.ALLOW_COMMENTS,true); baseMapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES,true); baseMapper.configure(JsonParser.Feature.ALLOW_SINGLE_QUOTES,true); // 配置两个副本 prettyMapper1 = baseMapper.copy(); prettyMapper2 = baseMapper.copy(); // 高级配置 prettyMapper1.enable(SerializationFeature.INDENT_OUTPUT); prettyMapper1.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss")); prettyMapper1.enable(SerializationFeature.WRITE_ENUMS_USING_TO_STRING); // 禁用序列化日期为timestamps prettyMapper1.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS); prettyMapper1.configure(JsonGenerator.Feature.ESCAPE_NON_ASCII,false); // Json格式化展示 prettyMapper2.setSerializationInclusion(JsonInclude.Include.NON_NULL); prettyMapper2.enable(SerializationFeature.INDENT_OUTPUT); prettyMapper2.configure(JsonGenerator.Feature.ESCAPE_NON_ASCII,true); prettyMapper2.enable(SerializationFeature.WRITE_ENUMS_USING_INDEX); nonEmptyMapper = new ObjectMapper(); nonEmptyMapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY); nonEmptyMapper.enable(SerializationFeature.INDENT_OUTPUT); nonEmptyMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss")); } @Test public void testReadValue() throws IOException { String json = "{\n" + " \"name\" : \"发如雪\",\n" + " \"now\" : \"2015-12-17 17:25:13\",\n" + " \"sexy\" : \"MEN\"\n" + "}"; TestBean testBean = nonEmptyMapper.readValue(json,TestBean.class); System.out.println(testBean.toString()); } @Test public void testWriteValue() throws IOException { TestBean testBean = new TestBean("发如雪",Sexy.MEN); System.out.println(prettyMapper1.writeValueAsString(testBean)); System.out.println(prettyMapper2.writeValueAsString(testBean)); System.out.println(nonEmptyMapper.writeValueAsString(testBean)); } } class TestBean{ private String name; private String course; private Date now; private Sexy sexy; public TestBean(){} public TestBean(String name,Sexy sexy){ this.name = name; this.sexy = sexy; this.now = new Date(); } public Date getNow() { return now; } public void setNow(Date now) { this.now = now; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Sexy getSexy() { return sexy; } public void setSexy(Sexy sexy) { this.sexy = sexy; } public String getCourse() { return course; } public void setCourse(String course) { this.course = course; } @Override public String toString() { return "TestBean{" + "name='" + name + '\'' + ", course='" + course + '\'' + ", now=" + now + ", sexy=" + sexy + '}'; } } enum Sexy{ MEN("男","M"),WOMEN("女","W"); private String text; private String code; private Sexy(String text,String code){ this.text = text; this.code = code; } public String getText() { return text; } public String getCode() { return code; } @Override public String toString() { return "{\"text\":\""+getText()+"\",\"code\":\""+getCode()+"\"}"; } }