{title:'POJO Categories'}

In general, Juneau allows for marshalling for a wide variety of POJO types including:

The following chart shows POJOs categorized into groups and whether they can be serialized or parsed:

General POJO serialization/parsing support
GroupDescriptionExamplesCan
serialize?
Can
parse?
1 Java primitives and primitive objects
  • {@code String}
  • {@code Integer}
  • {@code Float}
  • {@code Boolean}
yes yes
2 Java Collections Framework objects, Java arrays, Java Optionals      
2a With standard keys/values
Map keys are group [1, 4a, 6a] objects.
Map, Collection, Optional, and array values are group [1, 2, 3ac, 4a, 6a] objects.
  • HashSet<String,Integer>
  • TreeMap<Integer,Bean>
  • List<int[][]>
  • Bean[]
  • Optional<Bean>
yes yes
2b With non-standard keys/values
Map keys are group [2, 3, 4b, 5, 6b, 7] objects.
Map, Collection, and array values are group [3b, 4b, 5, 6b, 7] objects.
  • HashSet<Bean,Integer>
  • TreeMap<Integer,Reader>
  • Optional<Reader>
yes no
3 Java Beans      
3a With standard properties
These are beans that have one or more properties defined by public getter or public fields.
Properties can also be defined as final read-only fields and passed in as constructor args.
Property values are group [1, 2, 3ac, 4a, 6a] objects.
  yes yes
3b With non-standard properties or not true beans
These include true beans that have one or more properties defined by getter and setter methods or properties but property types include group [3b, 4b, 5, 6b, 7] objects.
This also includes classes that look like beans but aren't true beans. For example, classes that have getters but not setters, or classes without no-arg constructors.
  yes no
3c Virtual beans
These are unimplemented bean interfaces with properties of type [1, 2, 3ac, 4a, 6a] objects.
Parsers will automatically create interface proxies on top of BeanMap instances.
  yes yes
3d Read-only beans without setters
The same as 3a but without property setters or constructor args.
  yes no
4 Swapped objects
These are objects that are not directly serializable but have {@link oaj.swap.ObjectSwap ObjectSwaps} associated with them. The purpose of a POJO swap is to convert an object to another object that is easier to serialize and parse. For example, the {@link oaj.swaps.TemporalDateSwap.IsoLocalDateTime} class can be used to serialize {@link java.util.Date} objects to ISO8601 strings, and parse them back into {@link java.util.Date} objects.
     
4a 2-way swapped to group [1, 2a, 3ac] objects
For example, a swap that converts a {@code Date} to a {@code String}.
  • java.util.Date
  • java.util.GregorianCalendar
yes yes
4b 1-way swapped to group [1, 2, 3] objects
For example, a swap that converts an {@code Iterator} to a {@code List}. This would be one way, since you cannot reconstruct an {@code Iterator}.
  • java.util.Iterator
yes no
5 Readers and InputStreams
Contents are serialized directly to the output stream or writer.
Typically used for low-level language-specific replacement of POJOs using per-Media-Type POJO swaps.
  • {@code FileInputStream}
  • {@code StringReader}
yes no
6 Non-serializable objects with standard methods for converting to a serializable form
     
6a Classes with a method that converts it to a serializable form:
  • public X swap(BeanSession); where X is in groups [1, 2a, 3ac].
  • public String toString(); where the string is any meaningful data.
And a method that converts it back into the original object:
  • public static T fromString(String);
  • public static T valueOf(String);
  • public static T parse(String);
  • public static T parseString(String);
  • public static T forName(String);
  • public static T forString(String);
  • public T(X); where X is in groups [1, 2a, 3ac].
  • public static T unswap(BeanSession,X); where X is in groups [1, 2a, 3ac].
  • java.lang.Class
  • java.sql.Time
  • java.sql.Timestamp
  • java.text.MessageFormat
  • java.text.NumberFormat
  • java.util.Date
  • java.util.UUID
  • java.util.logging.Level
  • javax.xml.bind.DatatypeConverter
yes yes
6b Classes that only have a method to convert to a serializable form:
  • public X swap(BeanSession); where X is in groups [1, 2, 3].
  • public String toString(); where the string is any meaningful data.
  yes no
7 All other objects
Anything that doesn't fall into one of the groups above are simply converted to {@code Strings} using the {@code toString()} method.
  yes no
Serializers are designed to work on tree-shaped POJO models. These are models where there are no referential loops (e.g. leaves with references to nodes, or nodes in one branch referencing nodes in another branch). There is a serializer setting {@code detectRecursions} to look for and handle these kinds of loops (by setting these references to null) but it is not enabled by default since it introduces a moderate performance penalty.
POJOs convertible to/from Strings

A separate category exists for POJOs that can be converted to and from Strings. These are used in places such as:

As a general rule, all POJOs are converted to Strings using the toString() method. However, there is one exception:

POJOs are convertible from Strings using any of the following (matched in the specified order):

Exceptions exist for the following classes:

POJOs convertible to/from other types

POJOs are also converted to various other types in places such as the Open-API serializers and parsers. In this section, the type being converted to will be referred to as X.

POJOs are considered convertible from X if it has any of the following (matched in the specified order):

POJOs are considered convertible from X if any of the reverse of above are true.