0
# Jackson Modules
1

2
Dropwizard Jackson provides several custom Jackson modules that extend serialization capabilities for specific types and use cases commonly found in Dropwizard applications.
3

4
## CaffeineModule
5

6
Jackson module that provides serialization and deserialization support for Caffeine cache specifications.
7

8
```java { .api }
9
public class CaffeineModule extends Module {
10
    public String getModuleName() // Returns "CaffeineModule"
11
    public Version version()
12
    public void setupModule(SetupContext context)
13
}
14
```
15

16
**Supported Types**:
17
- `com.github.benmanes.caffeine.cache.CaffeineSpec`
18

19
**Serialization Behavior**:
20
- Serializes CaffeineSpec objects to their parseable string representation
21
- Deserializes string values back to CaffeineSpec objects
22
- Handles "off" and "disabled" as special values for disabled caching
23

24
**Usage Example**:
25
```java
26
ObjectMapper mapper = Jackson.newObjectMapper(); // CaffeineModule automatically included
27

28
CaffeineSpec spec = CaffeineSpec.parse("maximumSize=1000,expireAfterWrite=30s");
29
String json = mapper.writeValueAsString(spec);
30
// Result: "maximumSize=1000,expireAfterWrite=30s"
31

32
CaffeineSpec deserialized = mapper.readValue(json, CaffeineSpec.class);
33
```
34

35
## FuzzyEnumModule
36

37
Jackson module that provides permissive enum deserialization, handling common formatting variations.
38

39
```java { .api }
40
public class FuzzyEnumModule extends Module {
41
    public String getModuleName() // Returns "permissive-enums"
42
    public Version version()
43
    public void setupModule(SetupContext context)
44
}
45
```
46

47
**Deserialization Features**:
48
- **Case Insensitive**: Matches enum values regardless of case
49
- **Whitespace Handling**: Strips leading and trailing whitespace
50
- **Character Normalization**: Converts dashes and periods to underscores
51
- **Flexible Matching**: Uses `Enums.fromStringFuzzy()` utility for permissive matching
52
- **Error Handling**: Provides clear error messages listing accepted values when deserialization fails
53

54
**Behavior Conditions**:
55
- Only applies when no `@JsonCreator` annotation is present
56
- Disabled when `READ_ENUMS_USING_TO_STRING` feature is enabled
57
- Disabled when `READ_UNKNOWN_ENUM_VALUES_AS_NULL` feature is enabled
58
- Disabled when `READ_UNKNOWN_ENUM_VALUES_USING_DEFAULT_VALUE` feature is enabled
59
- Disabled when enum fields have Jackson annotations from `com.fasterxml.jackson.annotation` package
60

61
**Usage Example**:
62
```java
63
public enum Status {
64
    ACTIVE, INACTIVE, PENDING
65
}
66

67
ObjectMapper mapper = Jackson.newObjectMapper(); // FuzzyEnumModule automatically included
68

69
// All of these will deserialize to Status.ACTIVE:
70
Status active1 = mapper.readValue("\"active\"", Status.class);
71
Status active2 = mapper.readValue("\"ACTIVE\"", Status.class);
72
Status active3 = mapper.readValue("\" active \"", Status.class);
73
Status active4 = mapper.readValue("\"act-ive\"", Status.class);
74
```
75

76
## GuavaExtrasModule
77

78
Jackson module that provides serialization and deserialization support for Guava cache builder specifications.
79

80
```java { .api }
81
public class GuavaExtrasModule extends Module {
82
    public String getModuleName() // Returns "guava-extras"
83
    public Version version()
84
    public void setupModule(SetupContext context)
85
}
86
```
87

88
**Supported Types**:
89
- `com.google.common.cache.CacheBuilderSpec`
90

91
**Serialization Behavior**:
92
- Serializes CacheBuilderSpec objects to their parseable string representation
93
- Deserializes string values back to CacheBuilderSpec objects
94
- Handles "off" and "disabled" as special values for disabled caching
95

96
**Usage Example**:
97
```java
98
ObjectMapper mapper = Jackson.newObjectMapper(); // GuavaExtrasModule automatically included
99

100
CacheBuilderSpec spec = CacheBuilderSpec.parse("maximumSize=500,expireAfterAccess=10m");
101
String json = mapper.writeValueAsString(spec);
102
// Result: "maximumSize=500,expireAfterAccess=10m"
103

104
CacheBuilderSpec deserialized = mapper.readValue(json, CacheBuilderSpec.class);
105

106
// Special handling for disabled caches
107
CacheBuilderSpec disabled = mapper.readValue("\"disabled\"", CacheBuilderSpec.class);
108
// Results in CacheBuilderSpec.disableCaching()
109
```
110

111
## Module Registration
112

113
All modules are automatically registered when using Jackson factory methods:
114

115
```java
116
ObjectMapper mapper = Jackson.newObjectMapper();
117
// All three modules (CaffeineModule, FuzzyEnumModule, GuavaExtrasModule) are pre-registered
118

119
ObjectMapper minimal = Jackson.newMinimalObjectMapper();
120
// Only GuavaModule is registered (not the custom Dropwizard modules)
121
```
122

123
## Integration with Standard Modules
124

125
The custom modules work alongside standard Jackson modules that are also automatically registered:
126

127
- **GuavaModule**: Basic Guava collections support
128
- **ParameterNamesModule**: Constructor parameter name preservation
129
- **Jdk8Module**: Java 8 Optional and Stream support
130
- **JavaTimeModule**: JSR-310 time types (LocalDate, Instant, etc.)
131
- **Performance Modules**: Afterburner or Blackbird for optimization