jackson处理json-工具盒子

君子成人之美，不成人之恶。小人反是。------《论语》

介绍 {#介绍}

Jackson 的核心模块由三部分组成

jackson-core，核心包，提供基于"流模式"解析的相关 API，它包括 JsonPaser 和 JsonGenerator。 Jackson 内部实现正是通过高性能的流模式 API 的 JsonGenerator 和 JsonParser 来生成和解析 json。
jackson-annotations，注解包，提供标准注解功能。
jackson-databind ，数据绑定包，提供基于"对象绑定" 解析的相关 API （ ObjectMapper ）和"树模型" 解析的相关 API （JsonNode）；基于"对象绑定" 解析的 API 和"树模型"解析的 API 依赖基于"流模式"解析的 API。

用法 {#用法}

引入依赖

|---------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 | hljs plaintext <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.9.5</version> </dependency> 12345 |

jackson-databind 依赖 jackson-core 和 jackson-annotations，当添加 jackson-databind 之后， jackson-core 和 jackson-annotations 也随之添加到 Java 项目工程中。在添加相关依赖包之后，就可以使用 Jackson。

Jackson 最常用的 API 就是基于"对象绑定" 的 ObjectMapper。下面是一个 ObjectMapper 的使用的简单示例。

test

|------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 | hljs plaintext @Test public void test() throws IOException { ObjectMapper mapper = new ObjectMapper(); User user = new User(); user.set.. // 序列化 String jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(user); // 反序列化 user = mapper.readValue(jsonString, User.class); } 12345678910111213 |

ObjectMapper 通过 writeValue 系列方法将 java 对象序列化为 json，并将 json 存储成不同的格式：String（writeValueAsString）、Byte Array（writeValueAsBytes）、Writer、File、OutStream、DataOutput。

ObjectMapper 通过 readValue 系列方法从不同的数据源： String、Byte Array、Reader、File、URL、InputStream 中反序列化为 java 对象。

在调用 writeValue 或调用 readValue 方法之前，往往需要设置 ObjectMapper 的相关配置信息。这些配置信息应用 java 对象的所有属性上。示例如下：

|------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 | hljs plaintext //在反序列化时忽略在 json 中存在但 Java 对象不存在的属性 mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false); //在序列化时日期格式默认为 yyyy-MM-dd'T'HH:mm:ss.SSSZ mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false) //在序列化时忽略值为 null 的属性 mapper.setSerializationInclusion(Include.NON_NULL); //忽略值为默认值的属性 mapper.setDefaultPropertyInclusion(Include.NON_DEFAULT); 123456789 |

常用序列化与反序列化 {#常用序列化与反序列化}

1、序列化 {#1-序列化}

Jackson ObjectMapper提供了三种方法转换

|-----------------|---------------------------------------------------------------------------------| | 1 2 3 4 | hljs plaintext writeValue() writeValueAsString() writeValueAsBytes() 123 |

writeValue

|-------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 | hljs plaintext ObjectMapper objectMapper = new ObjectMapper(); Car car = new Car(); car.brand = "BMW"; car.doors = 4; objectMapper.writeValue(new FileOutputStream("data/output-2.json"), car); 1234567 |

writeValueAsString

|-------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 | hljs plaintext ObjectMapper objectMapper = new ObjectMapper(); Car car = new Car(); car.brand = "BMW"; car.doors = 4; String json = objectMapper.writeValueAsString(car); 1234567 |

writeValueAsBytes

|-------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 | hljs plaintext ObjectMapper objectMapper = new ObjectMapper(); Car car = new Car(); car.brand = "BMW"; car.doors = 4; byte[] jsonBytes = objectMapper.writeValueAsString(car); 1234567 |

2、时间类型格式化 {#2-时间类型格式化}

Jackson 默认会将java.util.Date对象转换成long值,同时也支持将时间转换成格式化的字符串

|-------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 | hljs plaintext SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd"); objectMapper.setDateFormat(dateFormat); String json = objectMapper.writeValueAsString(对象); 1234 |

3、反序列化读取方式 {#3-反序列化读取方式}

从json字符串读取

|-----------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 | hljs plaintext ObjectMapper objectMapper = new ObjectMapper(); String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }"; Car car = objectMapper.readValue(carJson, Car.class); 123 |

从json Reader读取

|-------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 | hljs plaintext ObjectMapper objectMapper = new ObjectMapper(); String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 4 }"; Reader reader = new StringReader(carJson); Car car = objectMapper.readValue(reader, Car.class); 1234 |

从json文件读取

|-----------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 | hljs plaintext ObjectMapper objectMapper = new ObjectMapper(); File file = new File("data/car.json"); Car car = objectMapper.readValue(file, Car.class); 123 |

从json网络文件地址读取

|-----------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 | hljs plaintext ObjectMapper objectMapper = new ObjectMapper(); URL url = new URL("file:data/car.json"); Car car = objectMapper.readValue(url, Car.class); 123 |

从流中读取

|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 | hljs plaintext ObjectMapper objectMapper = new ObjectMapper(); InputStream input = new FileInputStream("data/car.json"); Car car = objectMapper.readValue(input, Car.class); 123 |

从json字节数组中读取

|-------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 | hljs plaintext ObjectMapper objectMapper = new ObjectMapper(); String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }"; byte[] bytes = carJson.getBytes("UTF-8"); Car car = objectMapper.readValue(bytes, Car.class); 1234 |

4、反序列化不同类型 {#4-反序列化不同类型}

转换为数组

|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 | hljs plaintext String jsonArray = "[{\"brand\":\"ford\"}, {\"brand\":\"Fiat\"}]"; ObjectMapper objectMapper = new ObjectMapper(); Car[] cars = objectMapper.readValue(jsonArray, Car[].class); 123 |

转换为集合

|-----------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 | hljs plaintext String jsonArray = "[{\"brand\":\"ford\"}, {\"brand\":\"Fiat\"}]"; ObjectMapper objectMapper = new ObjectMapper(); List<Car> cars = objectMapper.readValue(jsonArray, new TypeReference<List<Car>>(){}); 123 |

转换为Map

|-----------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 | hljs plaintext String jsonObject = "{\"brand\":\"ford\", \"doors\":5}"; ObjectMapper objectMapper = new ObjectMapper(); Map<String, Object> jsonMap = objectMapper.readValue(jsonObject, new TypeReference<Map<String,Object>>(){}); 123 |

5、JSON树模型 {#5-json树模型}

Jackson 也提供了树模型（tree model）来生成和解析 json。若想修改或访问 json 部分属性，树模型是不错的选择。树模型由 JsonNode 节点组成

example

|------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 | hljs plaintext String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }"; ObjectMapper objectMapper = new ObjectMapper(); try { JsonNode node = objectMapper.readValue(carJson, JsonNode.class); JsonNode brandNode = node.get("brand"); String brand = brandNode.asText(); System.out.println("brand = " + brand); JsonNode doorsNode = node.get("doors"); int doors = doorsNode.asInt(); System.out.println("doors = " + doors); JsonNode array = node.get("owners"); JsonNode jsonNode = array.get(0); String john = jsonNode.asText(); System.out.println("john = " + john); JsonNode child = node.get("nestedObject"); JsonNode childField = child.get("field"); String field = childField.asText(); System.out.println("field = " + field); } catch (IOException e) { e.printStackTrace(); } 12345678910111213141516171819202122232425 |

JsonParser {#jsonparser}

JsonParser 提供很多方法来读取 json 信息，如 isClosed(), nextToken(), getValueAsString()等。若想单独创建 JsonParser，可以通过 JsonFactory() 的 createParser。

example

|------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | hljs plaintext String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }"; JsonFactory factory = new JsonFactory(); JsonParser parser = factory.createParser(carJson); 123 String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }"; JsonFactory factory = new JsonFactory(); JsonParser parser = factory.createParser(carJson); Car car = new Car(); while(!parser.isClosed()){ JsonToken jsonToken = parser.nextToken(); if(JsonToken.FIELD_NAME.equals(jsonToken)){ String fieldName = parser.getCurrentName(); System.out.println(fieldName); jsonToken = parser.nextToken(); if("brand".equals(fieldName)){ car.brand = parser.getValueAsString(); } else if ("doors".equals(fieldName)){ car.doors = parser.getValueAsInt(); } } } System.out.println("car.brand = " + car.brand); System.out.println("car.doors = " + car.doors); 12345678910111213141516171819202122232425 |

JsonGenerator {#jsongenerator}

JsonGenerator 有多种 write 方法以支持生成复杂的类型的 json，比如 writeArray，writeTree 等。若想单独创建 JsonGenerator，可以通过 JsonFactory() 的 createGenerator。

example

|---------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | hljs plaintext JsonFactory factory = new JsonFactory(); JsonGenerator generator = factory.createGenerator(new File("data/output.json"), JsonEncoding.UTF8); 123 JsonFactory factory = new JsonFactory(); JsonGenerator generator = factory.createGenerator(new File("data/output.json"), JsonEncoding.UTF8); generator.writeStartObject(); generator.writeStringField("brand", "Mercedes"); generator.writeNumberField("doors", 5); generator.writeEndObject(); generator.close(); 12345678910 |

也可以通过Reader, InputStream, URL, byte array 或 char array来创建JsonParser

配置相关属性 {#配置相关属性}

SerializationFeature（序列化相关属性）

DeserializationFeature（反序列化相关属性）

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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 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/****************************************************** */ /** * 反序列化时,遇到未知属性(那些没有对应的属性来映射的属性,并且没有任何setter或handler来处理这样的属性)时是否引起结果失败。默认为true */ FAIL_ON_UNKNOWN_PROPERTIES(true), /** * 反序列化时,遇到null属性映射在java基本数据类型（int或douuble）是否报异常。默认为false */ FAIL_ON_NULL_FOR_PRIMITIVES(false), /** * 反序列化时,遇到integer numbers属性映射在enum类型时，如果为true,numbers将不可以映射到enum中。默认为false */ FAIL_ON_NUMBERS_FOR_ENUMS(false), /** * 反序列化时，遇到类名错误或者map中id找不到时是否报异常。默认为true */ FAIL_ON_INVALID_SUBTYPE(true), /** * 反序列化时，遇到json数据存在两个相同的key时是否报异常。默认为false */ FAIL_ON_READING_DUP_TREE_KEY(false), /** * 反序列化时，遇到json属性字段为可忽略的是否报异常。默认为false */ FAIL_ON_IGNORED_PROPERTIES(false), /** * Feature that determines what happens if an Object Id reference is encountered * that does not refer to an actual Object with that id ("unresolved Object Id"): * either an exception is thrown (<code>true</code>), or a null object is used * instead (<code>false</code>). * Note that if this is set to <code>false</code>, no further processing is done; * specifically, if reference is defined via setter method, that method will NOT * be called. * * Feature is enabled by default, so that unknown Object Ids will result in an * exception being thrown, at the end of deserialization. */ FAIL_ON_UNRESOLVED_OBJECT_IDS(true), /** * Feature that determines what happens if one or more Creator properties (properties * bound to parameters of Creator method (constructor or static factory method)) * are missing value to bind to from content. * If enabled, such missing values result in a {@link JsonMappingException} being * thrown with information on the first one (by index) of missing properties. * If disabled, and if property is NOT marked as required, * missing Creator properties are filled * with <code>null values</code> provided by deserializer for the type of parameter * (usually null for Object types, and default value for primitives; but redefinable * via custom deserializers). * * Note that having an injectable value counts as "not missing". * * Feature is disabled by default, so that no exception is thrown for missing creator * property values, unless they are explicitly marked as `required`. * * @since 2.6 */ FAIL_ON_MISSING_CREATOR_PROPERTIES(false), /** * Feature that determines what happens if one or more Creator properties (properties * bound to parameters of Creator method (constructor or static factory method)) * are bound to null values - either from the JSON or as a default value. This * is useful if you want to avoid nulls in your codebase, and particularly useful * if you are using Java or Scala optionals for non-mandatory fields. * Feature is disabled by default, so that no exception is thrown for missing creator * property values, unless they are explicitly marked as `required`. * * @since 2.8 */ FAIL_ON_NULL_CREATOR_PROPERTIES(false), /** * Feature that determines what happens when a property annotated with * {@link com.fasterxml.jackson.annotation.JsonTypeInfo.As#EXTERNAL_PROPERTY} is missing, * but associated type id is available. If enabled, {@link JsonMappingException} is always * thrown when property value is missing (if type id does exist); * if disabled, exception is only thrown if property is marked as `required`. * * Feature is enabled by default, so that exception is thrown when a subtype property is * missing. * * @since 2.9 */ FAIL_ON_MISSING_EXTERNAL_TYPE_ID_PROPERTY(true), /** * Feature that determines behaviour for data-binding after binding the root value. * If feature is enabled, one more call to * {@link com.fasterxml.jackson.core.JsonParser#nextToken} is made to ensure that * no more tokens are found (and if any is found, * {@link com.fasterxml.jackson.databind.exc.MismatchedInputException} is thrown); if * disabled, no further checks are made. * * Feature could alternatively be called <code>READ_FULL_STREAM</code>, since it * effectively verifies that input stream contains only as much data as is needed * for binding the full value, and nothing more (except for possible ignorable * white space or comments, if supported by data format). * * Feature is disabled by default (so that no check is made for possible trailing * token(s)) for backwards compatibility reasons. * * @since 2.9 */ FAIL_ON_TRAILING_TOKENS(false), /** * Feature that determines whether Jackson code should catch * and wrap {@link Exception}s (but never {@link Error}s!) * to add additional information about * location (within input) of problem or not. If enabled, * most exceptions will be caught and re-thrown (exception * specifically being that {@link java.io.IOException}s may be passed * as is, since they are declared as throwable); this can be * convenient both in that all exceptions will be checked and * declared, and so there is more contextual information. * However, sometimes calling application may just want "raw" * unchecked exceptions passed as is. * * Feature is enabled by default. */ WRAP_EXCEPTIONS(true), /* /****************************************************** /* 结构转换特性 /****************************************************** */ /** * 反序列化时，是否接受单个value转为List，如json字符串中单个String值可以转为Bean中的List。默认为false */ ACCEPT_SINGLE_VALUE_AS_ARRAY(false), /** * 将json中的数组映射到实体单值中 * 例如 {"aaa":[{"value":"wewfewfew"}],"bbb":[{"value":"wefwefw"}]} * 转换为 * public class MyEntity{ * private String aaa; * private String bbb; * } */ UNWRAP_SINGLE_VALUE_ARRAYS(false), /** * 对于设置了@JsonRootName实体转换的json，可通过该属性进行实体转换 */ UNWRAP_ROOT_VALUE(false), /* /****************************************************** /* 值转换特性 /****************************************************** */ /** * 反序列化时，是否将空字符传转化为null。默认为false */ ACCEPT_EMPTY_STRING_AS_NULL_OBJECT(false), /** * 反序列化时，是否将空数组转换为null。默认为false */ ACCEPT_EMPTY_ARRAY_AS_NULL_OBJECT(false), /** * 反序列化时，是否可将JSON float值被反序列化为 int 、 long 或 BigInteger。默认为true */ ACCEPT_FLOAT_AS_INT(true), /** * Feature that determines standard deserialization mechanism used for * Enum values: if enabled, Enums are assumed to have been serialized using * return value of <code>Enum.toString()</code>; * if disabled, return value of <code>Enum.name()</code> is assumed to have been used. * * Note: this feature should usually have same value * as {@link SerializationFeature#WRITE_ENUMS_USING_TO_STRING}. * * Feature is disabled by default. */ READ_ENUMS_USING_TO_STRING(false), /** * Feature that allows unknown Enum values to be parsed as null values. * If disabled, unknown Enum values will throw exceptions. * * Note that in some cases this will basically ignore unknown Enum values; * this is the keys for keys of {@link java.util.EnumMap} and values * of {@link java.util.EnumSet} (because nulls are not accepted in these * cases). * * Feature is disabled by default. * * @since 2.0 */ READ_UNKNOWN_ENUM_VALUES_AS_NULL(false), /** * Feature that allows unknown Enum values to be ignored and a predefined value specified through * {@link com.fasterxml.jackson.annotation.JsonEnumDefaultValue @JsonEnumDefaultValue} annotation. * If disabled, unknown Enum values will throw exceptions. * If enabled, but no predefined default Enum value is specified, an exception will be thrown as well. * * Feature is disabled by default. * * @since 2.8 */ READ_UNKNOWN_ENUM_VALUES_USING_DEFAULT_VALUE(false), /** * 反序列化时，是否使用long解析时间。默认为true */ READ_DATE_TIMESTAMPS_AS_NANOSECONDS(true), /** * Feature that specifies whether context provided {@link java.util.TimeZone} * ({@link DeserializationContext#getTimeZone()} should be used to adjust Date/Time * values on deserialization, even if value itself contains timezone information. * If enabled, contextual <code>TimeZone</code> will essentially override any other * TimeZone information; if disabled, it will only be used if value itself does not * contain any TimeZone information. * * Note that exact behavior depends on date/time types in question; and specifically * JDK type of {@link java.util.Date} does NOT have in-built timezone information * so this setting has no effect. * Further, while {@link java.util.Calendar} does have this information basic * JDK {@link java.text.SimpleDateFormat} is unable to retain parsed zone information, * and as a result, {@link java.util.Calendar} will always get context timezone * adjustment regardless of this setting. * * * Taking above into account, this feature is supported only by extension modules for * Joda and Java 8 date/tyime datatypes. * * @since 2.2 */ ADJUST_DATES_TO_CONTEXT_TIME_ZONE(true), /* /****************************************************** /* Other /****************************************************** */ /** * Feature that determines whether {@link ObjectReader} should * try to eagerly fetch necessary {@link JsonDeserializer} when * possible. This improves performance in cases where similarly * configured {@link ObjectReader} instance is used multiple * times; and should not significantly affect single-use cases. * * Note that there should not be any need to normally disable this * feature: only consider that if there are actual perceived problems. * * Feature is enabled by default. * * @since 2.1 */ EAGER_DESERIALIZER_FETCH(true); private final boolean _defaultState; private final int _mask; private DeserializationFeature(boolean defaultState) { _defaultState = defaultState; _mask = (1 << ordinal()); } @Override public boolean enabledByDefault() { return _defaultState; } @Override public int getMask() { return _mask; } @Override public boolean enabledIn(int flags) { return (flags & _mask) != 0; } } 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326 |

MapperFeature

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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 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for a field does not necessarily lead to ignoral of getters or setters * but just ignoring the use of field for access. * * @since 2.6 */ PROPAGATE_TRANSIENT_MARKER(false), /* /****************************************************** /* Introspection-based property auto-detection /****************************************************** */ /** * 该特性决定是否使用creator方法来根据公共构造函数以及名字为"valueOf"的静态单参数方法自动检测。 */ AUTO_DETECT_CREATORS(true), /** * 这个特性决定是否非静态字段被当做属性。如果true，则所有公共成员字段都被当做属性，否则只有注解，才会被当做属性字段。 */ AUTO_DETECT_FIELDS(true), /** * 该特性决定是否使用"getter"方法来根据标准bean命名转换方式来自动检测。如果true，则所有公共的带有一个参数 * 并且前缀为get的方法都将被当做getter方法。如果false，只会把显式注解的作为getter方法。 */ AUTO_DETECT_GETTERS(true), /** * 获取getter方法，前缀为is */ AUTO_DETECT_IS_GETTERS(true), /** * 该特性决定是否使用"setter"方法来根据标准bean命名转换方式来自动检测。如果true，则所有公共的带有一个参数 * 并且前缀为set的方法都将被当做setter方法。如果false，只会把显式注解的作为setter方法。 */ AUTO_DETECT_SETTERS(true), /** * 如果这个配置为false时，只有存在对应的构造器、setter或者field时，才调用getter */ REQUIRE_SETTERS_FOR_GETTERS(false), /** * Feature that determines whether member fields declared as 'final' may * be auto-detected to be used mutators (used to change value of the logical * property) or not. If enabled, 'final' access modifier has no effect, and * such fields may be detected according to usual visibility and inference * rules; if disabled, such fields are NOT used as mutators except if * explicitly annotated for such use. * * Feature is enabled by default, for backwards compatibility reasons. * * @since 2.2 */ ALLOW_FINAL_FIELDS_AS_MUTATORS(true), /** * Feature that determines whether member mutators (fields and * setters) may be "pulled in" even if they are not visible, * as long as there is a visible accessor (getter or field) with same name. * For example: field "value" may be inferred as mutator, * if there is visible or explicitly marked getter "getValue()". * If enabled, inferring is enabled; otherwise (disabled) only visible and * explicitly annotated accessors are ever used. * * Note that 'getters' are never inferred and need to be either visible (including * bean-style naming) or explicitly annotated. * * Feature is enabled by default. * * @since 2.2 */ INFER_PROPERTY_MUTATORS(true), /** * Feature that determines handling of <code>java.beans.ConstructorProperties<code> * annotation: when enabled, it is considered as alias of * {@link com.fasterxml.jackson.annotation.JsonCreator}, to mean that constructor * should be considered a property-based Creator; when disabled, only constructor * parameter name information is used, but constructor is NOT considered an explicit * Creator (although may be discovered as one using other annotations or heuristics). * * Feature is mostly used to help interoperability with frameworks like Lombok * that may automatically generate <code>ConstructorProperties</code> annotation * but without necessarily meaning that constructor should be used as Creator * for deserialization. * * Feature is enabled by default. * * @since 2.9 */ INFER_CREATOR_FROM_CONSTRUCTOR_PROPERTIES(true), /* /****************************************************** /* Access modifier handling /****************************************************** */ /** * Feature that determines whether method and field access * modifier settings can be overridden when accessing * properties. If enabled, method * {@link java.lang.reflect.AccessibleObject#setAccessible} * may be called to enable access to otherwise unaccessible objects. * * Note that this setting may have significant performance implications, * since access override helps remove costly access checks on each * and every Reflection access. If you are considering disabling * this feature, be sure to verify performance consequences if usage * is performance sensitive. * Also note that performance effects vary between Java platforms * (JavaSE vs Android, for example), as well as JDK versions: older * versions seemed to have more significant performance difference. * * Conversely, on some platforms, it may be necessary to disable this feature * as platform does not allow such calls. For example, when developing * Applets (or other Java code that runs on tightly restricted sandbox), * it may be necessary to disable the feature regardless of performance effects. * * Feature is enabled by default. */ CAN_OVERRIDE_ACCESS_MODIFIERS(true), /** * Feature that determines that forces call to * {@link java.lang.reflect.AccessibleObject#setAccessible} even for * <code>public</code> accessors -- that is, even if no such call is * needed from functionality perspective -- if call is allowed * (that is, {@link #CAN_OVERRIDE_ACCESS_MODIFIERS} is set to true). * The main reason to enable this feature is possible performance * improvement as JDK does not have to perform access checks; these * checks are otherwise made for all accessors, including public ones, * and may result in slower Reflection calls. Exact impact (if any) * depends on Java platform (Java SE, Android) as well as JDK version. * * Feature is enabled by default, for legacy reasons (it was the behavior * until 2.6) * * @since 2.7 */ OVERRIDE_PUBLIC_ACCESS_MODIFIERS(true), /* /****************************************************** /* Type-handling features /****************************************************** */ /** * 是否使用运行时动态类型，还是声明的静态类型 */ USE_STATIC_TYPING(false), /* /****************************************************** /* View-related features /****************************************************** */ /** * 该特性决定拥有view注解的属性是否在JSON序列化视图中。如果true，则非注解视图，也包含； * 否则，它们将会被排除在外。 */ DEFAULT_VIEW_INCLUSION(true), /* /****************************************************** /* Generic output features /****************************************************** */ /** * 是否对属性使用排序，默认排序按照字母顺序 */ SORT_PROPERTIES_ALPHABETICALLY(false), /* /****************************************************** /* Name-related features /****************************************************** */ /** * 反序列化是否忽略大小写 */ ACCEPT_CASE_INSENSITIVE_PROPERTIES(false), /** * Feature that determines if Enum deserialization should be case sensitive or not. * If enabled, Enum deserialization will ignore case, that is, case of incoming String * value and enum id (dependant on other settings, either `name()`, `toString()`, or * explicit override) do not need to match. * * Feature is disabled by default. * * @since 2.9 */ ACCEPT_CASE_INSENSITIVE_ENUMS(false), /** * Feature that can be enabled to make property names be * overridden by wrapper name (usually detected with annotations * as defined by {@link AnnotationIntrospector#findWrapperName}. * If enabled, all properties that have associated non-empty Wrapper * name will use that wrapper name instead of property name. * If disabled, wrapper name is only used for wrapping (if anything). * * Feature is disabled by default. * * @since 2.1 */ USE_WRAPPER_NAME_AS_PROPERTY_NAME(false), /** * Feature that may be enabled to enforce strict compatibility with * Bean name introspection, instead of slightly different mechanism * Jackson defaults to. * Specific difference is that Jackson always lower cases leading upper-case * letters, so "getURL()" becomes "url" property; whereas standard Bean * naming only lower-cases the first letter if it is NOT followed by * another upper-case letter (so "getURL()" would result in "URL" property). * * Feature is disabled by default for backwards compatibility purposes: earlier * Jackson versions used Jackson's own mechanism. * * @since 2.5 */ USE_STD_BEAN_NAMING(false), /** * Feature that when enabled will allow explicitly named properties (i.e., fields or methods * annotated with {@link com.fasterxml.jackson.annotation.JsonProperty}("explicitName")) to * be re-named by a {@link PropertyNamingStrategy}, if one is configured. * * Feature is disabled by default. * * @since 2.7 */ ALLOW_EXPLICIT_PROPERTY_RENAMING(false), /* /****************************************************** /* Coercion features /****************************************************** */ /** * Feature that determines whether coercions from secondary representations are allowed * for simple non-textual scalar types: numbers and booleans. This includes `primitive` * types and their wrappers, but excludes `java.lang.String` and date/time types. * * When feature is disabled, only strictly compatible input may be bound: numbers for * numbers, boolean values for booleans. When feature is enabled, conversions from * JSON String are allowed, as long as textual value matches (for example, String * "true" is allowed as equivalent of JSON boolean token `true`; or String "1.0" * for `double`). * * Note that it is possible that other configurability options can override this * in closer scope (like on per-type or per-property basis); this is just the global * default. * * Feature is enabled by default (for backwards compatibility since this was the * default behavior) * * @since 2.9 */ ALLOW_COERCION_OF_SCALARS(true), /* /****************************************************** /* Other features /****************************************************** */ /** * Feature that determines whether multiple registrations of same module * should be ignored or not; if enabled, only the first registration call * results in module being called, and possible duplicate calls are silently * ignored; if disabled, no checking is done and all registration calls are * dispatched to module. * * Definition of "same module" is based on using {@link Module#getTypeId()}; * modules with same non-null <code>type id</code> are considered same for * purposes of duplicate registration. This also avoids having to keep track * of actual module instances; only ids will be kept track of (and only if * this feature is enabled). * * Feature is enabled by default. * * @since 2.5 */ IGNORE_DUPLICATE_MODULE_REGISTRATIONS(true), /** * Setting that determines what happens if an attempt is made to explicitly * "merge" value of a property, where value does not support merging; either * merging is skipped and new value is created (<code>true</code>) or * an exception is thrown (false). * * Feature is disabled by default since non-mergeable property types are ignored * even if defaults call for merging, and usually explicit per-type or per-property * settings for such types should result in an exception. * * @since 2.9 */ IGNORE_MERGE_FOR_UNMERGEABLE(true); private final boolean _defaultState; private final int _mask; private MapperFeature(boolean defaultState) { _defaultState = defaultState; _mask = (1 << ordinal()); } @Override public boolean enabledByDefault() { return _defaultState; } @Override public int getMask() { return _mask; } @Override public boolean enabledIn(int flags) { return (flags & _mask) != 0; } } 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350351352353354355356357358 |

JsonParser.Feature（解析器特性）

JsonGenerator

JsonFactory

xml实体互转 {#xml实体互转}

引入依赖

|---------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 | hljs plaintext <dependency> <groupId>com.fasterxml.jackson.dataformat</groupId> <artifactId>jackson-dataformat-xml</artifactId> <version>2.9.5</version> </dependency> 12345 |

使用

|------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 | hljs plaintext /* * Java对象转xml */ @Test public void testGenXml(){ XmlMapper xmlMapper = new XmlMapper(); Book book = new Book("Think in Java",100); try { String xmlStr = xmlMapper.writeValueAsString(book); System.out.println(xmlStr); } catch (JsonProcessingException e) { e.printStackTrace(); } } /* * xml转Java对象 */ @Test public void testGenObjByXml(){ XmlMapper xmlMapper = new XmlMapper(); String xmlStr = "<Book><name>Think in Java</name><price>100</price></Book>"; try { Book book = xmlMapper.readValue(xmlStr, Book.class); System.out.println(book); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } 12345678910111213141516171819202122232425262728293031 |

参考网站

https://github.com/FasterXML/jackson-docs

http://www.baeldung.com/jackson

https://www.ibm.com/developerworks/cn/java/jackson-advanced-application/index.html

http://tutorials.jenkov.com/java-json/boon-objectmapper.html