JarCastingcodec
What's this?
codec is a java serialization library. There are many like it, but this one is ours. Codec has its own reflection toolset, but we are moving to wards using more and more jackson in the back end. Currently, the most notable features are those that are built on top of jackson-databind and typesafe-config.
Codec:
- Supports both annotation-based and config-based settings.
- Flexible plugin system for decentralized, polymorphic handling.
- Default values on a per class and a per alias basis.
- Override almost anything with system properties via typesafe-config.
- Unambiguously enforce required values.
- Jsr-303 validation via hibernate-validator.
- Easily integrates anywhere that jackson does (most places).
- Extra-mile niceties for human-generated json/hocon/config files.
Currently supported formats:
- JSON
- HOCON
- Jackson supported formats
- Bin2: (deprecated) binary format.
Basic Use
For a simple POJO like this one ruthlessly lifted from jackson's readme...
// Note: can use getters/setters as well; here we just use public fields directly:
public class MyValue {
public String name;
public int age;
// NOTE: if using getters/setters, can keep fields `protected` or `private`
}
Simple deserialization can be done like this.
Configs.decodeObject(MyValue.class, "name = New Friend, age = 1");
Note that the string can be json or hocon (like it is here). The library parameter is annotated with @Syntax("HOCON") so if your IDE supports it, you'll get syntax highlighting right in the editor. (For intellij, install the scala plugin to get hocon support and then set the language annotation class to javax.annotation.Syntax via settings/language injections/advanced).
Set default field values (maybe in a file named application.conf or via system properties):
fully.qualified.name.MyValue {
name = Default Friend
age = 20
}
Then you could just do:
Configs.newDefault(MyValue.class);
Plugins
Categories can be defined by annotations and/ or config. The only non-jackson annotation is @Pluggable though.
@Pluggable("hasher")
public interface HashFunction {
long hash(Object toBeHashed);
}
plugins.hasher {
// optionally specify _class = com.addthis.codec.HashFunction
// may not make sense for categories with static methods, but allows
// lookups without the @Pluggable annotation, validates sub-types, and
// short subtype paths (com.addthis.codec.SubClass -> SubClass)
}
Then let's say we have this implementation either in our project or downstream.
public class SuperFastHash implements HashFunction {
private final long theBestNumber;
public SuperFastHash(@JsonProperty("seed") long seed) {
this.theBestNumber = seed;
}
public long hash(Object toBeHashed) {
return theBestNumber;
}
}
Let's add our guy to the plugin definition (we could also just put -Dplugins.hasher.fast=SuperFastHash on the command line or split the plugin definition across entirely different files or projects).
plugins.hasher {
_class = com.addthis.codec.HashFunction
fast = SuperFastHash
}
Now any of these will work (and others besides, of course).
Configs.decodeObject(HashFunction.class, "type = fast, seed = 4");
Configs.decodeObject(HashFunction.class, "fast { seed = 5 }");
Configs.decodeObject("hasher.fast.seed = 6");
We can go a step further and do
plugins.hasher {
fast {
_class = SuperFastHash
_primary = seed // assume non-object json values belong to this field
seed = 20 // new default value for seed
}
// create an alias for the fast type; recursively inherits settings, so it also has _primary defined
exactly-pi {
_class = fast
seed = 3
}
// if no type information can be found or inferred, we'll try exactly-pi
_default = exactly-pi
}
// using _primary
Configs.decodeObject(HashFunction.class, "fast = 32");
// using any and all defaults
Configs.decodeObject(HashFunction.class, "fast {}");
One more notable example -- lists where ever. This functionality is useful for lots of cases where a list has a single, intuitive meaning like "an input source or a bunch of input sources combined together" or "a filter or a bunch of filters in a row".
public class CompositeHash implements HashFunction {
private final HashFunction[] hashes;
public CompositeHash(@JsonProperty("hashes") HashFunction[] hashes) {
this.hashes = hashes;
}
public long hash(Object toBeHashed) {
long total = 0;
for (HashFunction hashFunction : hashes) {
total += hashFunction.hash(toBeHashed);
}
return total;
}
}
plugins.hasher {
sum { _class = CompositeHash, _primary = hashes }
// now anytime we are expecting a HashFunction and instead find an array, turn it into a CompositeHash
_array = sum
}
Configs.decodeObject("hasher = [{fast = 999}, {exactly-pi {}}]");
Extras/ quirks/ toggleable things
-
error to config location (ie. line number) reporting is accurate for hocon strings/files or even config objects derived therefrom. There are a few extra bug fixes on top of the latest jackson release that help make this possible. Those fixes help generic json reporting as well, but to a lesser extent.
-
@Time(TimeUnit) and @Bytes annotations that will preprocess any field/ parameter by converting values of the form "number unit" like "14 days" to the expected TimeUnit or plain bytes. Already valid numbers are left alone to make migration easy/ optional.
-
required fields are actually required. Specify with either @JsonProperty(required = true) or @FieldConfig(required = true). Often easier to reason about and document than preconditions on setters/ constructors or after-the-fact jsr-303 validation (especially for primitives).
-
type to class resolution tries the plugin map, jackson annotations, and then direct Class.forName lookups using all possible package prefixes of the base class (or just the full type string if there is no base class).
-
type inclusion is likewise flexible. it is analagous to the combination of several jackson inclusion types. The type field is checked first (which can be customized per category via the _field setting), then if it is a single key-value'd object, the single key is checked, then inlined types (declared using
_inline = trueas a subtype/ alias setting), then _default types. -
generic enum names are not case sensitive
-
'unknown properties' cause an exception by default, but also by default, unknown properties starting with an underscore (_) are ignored without malice. This gives some flexibility for custom meta data and stash points for hocon substitution targets.
-
unknown properties encountered during deserialization may optionally (disabled by default) be ignored if they are known to be written by the class in question (ie. write-only properties).
-
null values are not written to deserialized objects unless they have a special null representation like guava/java8 Optionals. This is to give 'user space things' like custom types and aliases more flexibility to control inheritance but still give developers/admins guarantees over behavior. eg. if I define a field like
int myField = 5in code, then I probably won't also flag it as required, but on the other hand, if it is being over written to 0, then at least one person involved should actively desire that rather than occuring when someone uses the otherwise ambiguous null -- which likely means unset rather than 'the java default for primitive integers'. -
fields can be read or write only without using extra, explicit getters/setters by using @FieldConfig(readonly = true) or (writeonly = true). However, that only works in the absence of other @JsonProperty annotations.
java version
codec versions 3.3.0 and earlier require java 7. Later versions require java 8, but may run under 7 with a bit of fiddling.
Building
codec uses Apache Maven which it is beyond the scope to detail. The super simple quick start is:
mvn test
Maven
<dependency>
<groupId>com.addthis</groupId>
<artifactId>codec</artifactId>
<version>latest-and-greatest</version>
</dependency>
You can either install locally, or releases will eventually make their way to maven central.
If you use a fat jar, or don't know what the words 'fat jar' mean, you may want to use something like the following for your build. You can maybe get away without it if you have no other dependencies that use either typesafe-config or codec. In that case, make sure not to define your own reference.conf.
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>2.3</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
<configuration>
<filters>
<filter>
<artifact>*:*</artifact>
<excludes>
<exclude>META-INF/*.SF</exclude>
<exclude>META-INF/*.DSA</exclude>
<exclude>META-INF/*.RSA</exclude>
</excludes>
</filter>
</filters>
<transformers>
<transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
<resource>reference.conf</resource>
</transformer>
<transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
<resource>application.conf</resource>
</transformer>
</transformers>
</configuration>
</execution>
</executions>
</plugin>
Administrative
Versioning
It's x.y.z where:
- x: something major happened
- y: next release
- z: bug fix only
License
codec is released under the Apache License Version 2.0. See Apache or the LICENSE for details.
