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Quick Overview
JsonPath is a Java library for reading JSON documents using XPath-like expressions. It allows developers to extract specific data from JSON structures using a simple query language, making it easier to navigate and retrieve information from complex JSON objects.
Pros
- Simple and intuitive query syntax similar to XPath
- Supports both read and write operations on JSON documents
- Lightweight and easy to integrate into existing Java projects
- Provides good performance for parsing and querying JSON data
Cons
- Limited support for advanced JSON manipulation operations
- Documentation could be more comprehensive and include more examples
- May not be as feature-rich as some alternative JSON parsing libraries
- Limited built-in support for handling large JSON files
Code Examples
- Reading a value from a JSON object:
String json = "{\"name\":\"John\", \"age\":30}";
JsonPath.parse(json).read("$.name");
// Output: "John"
- Filtering an array:
String json = "[{\"name\":\"John\", \"age\":30}, {\"name\":\"Jane\", \"age\":25}]";
List<Map<String, Object>> result = JsonPath.parse(json).read("$[?(@.age > 28)]");
// Output: [{name=John, age=30}]
- Updating a value in a JSON object:
String json = "{\"name\":\"John\", \"age\":30}";
DocumentContext context = JsonPath.parse(json);
context.set("$.age", 31);
String updatedJson = context.jsonString();
// Output: {"name":"John","age":31}
Getting Started
To use JsonPath in your Java project, add the following dependency to your Maven pom.xml
file:
<dependency>
<groupId>com.jayway.jsonpath</groupId>
<artifactId>json-path</artifactId>
<version>2.7.0</version>
</dependency>
For Gradle, add this to your build.gradle
file:
implementation 'com.jayway.jsonpath:json-path:2.7.0'
Then, you can start using JsonPath in your Java code:
import com.jayway.jsonpath.JsonPath;
String json = "{\"name\":\"John\", \"age\":30}";
String name = JsonPath.read(json, "$.name");
System.out.println(name); // Output: John
Competitor Comparisons
Java JsonPath implementation
Pros of JsonPath
- More actively maintained with recent updates
- Larger community and better documentation
- Supports a wider range of JsonPath expressions
Cons of JsonPath
- Slightly more complex API
- May have a steeper learning curve for beginners
- Potentially slower performance for simple queries
Code Comparison
JsonPath:
JsonPath.parse(json).read("$.store.book[*].author")
JsonPath>:
JsonPath.read(json, "$.store.book[*].author")
Additional Notes
Both libraries provide similar functionality for parsing and querying JSON data using JsonPath expressions. JsonPath is generally considered the more robust and feature-rich option, with better community support and documentation. However, JsonPath> may be simpler to use for basic queries and could potentially offer better performance in certain scenarios.
The choice between the two libraries depends on the specific requirements of your project, such as the complexity of your JsonPath queries, performance needs, and desired level of community support.
It's worth noting that JsonPath> seems to be less actively maintained, with fewer recent updates compared to JsonPath. This could potentially impact long-term support and compatibility with newer Java versions or JSON standards.
A reference implementation of a JSON package in Java.
Pros of JSON-java
- Simple and lightweight library for JSON parsing and manipulation
- Easy to use with straightforward API for creating and working with JSON objects
- No external dependencies, making it easy to integrate into projects
Cons of JSON-java
- Limited functionality compared to JsonPath, especially for complex JSON querying
- Lacks advanced features like JSON Path expressions for traversing JSON structures
- May require more manual coding for complex JSON operations
Code Comparison
JsonPath:
String json = "{\"store\":{\"book\":[{\"title\":\"Sayings of the Century\"}]}}";
String title = JsonPath.read(json, "$.store.book[0].title");
JSON-java:
String json = "{\"store\":{\"book\":[{\"title\":\"Sayings of the Century\"}]}}";
JSONObject jsonObject = new JSONObject(json);
String title = jsonObject.getJSONObject("store").getJSONArray("book").getJSONObject(0).getString("title");
JsonPath provides a more concise way to extract data from JSON using path expressions, while JSON-java requires manual navigation through the JSON structure. JsonPath is better suited for complex querying and data extraction, while JSON-java offers a simpler approach for basic JSON manipulation tasks.
Main Portal page for the Jackson project
Pros of Jackson
- More comprehensive JSON processing library with full read/write capabilities
- Highly customizable with numerous modules and extensions
- Better performance for large-scale JSON processing tasks
Cons of Jackson
- Steeper learning curve due to its extensive feature set
- Can be overkill for simple JSON parsing or querying tasks
- Larger library size and potential overhead for small projects
Code Comparison
JsonPath:
String json = "{ \"store\": { \"book\": [ { \"title\": \"Sayings of the Century\" } ] } }";
String title = JsonPath.read(json, "$.store.book[0].title");
Jackson:
ObjectMapper mapper = new ObjectMapper();
JsonNode root = mapper.readTree(json);
String title = root.at("/store/book/0/title").asText();
Key Differences
- JsonPath focuses on querying JSON data using path expressions
- Jackson provides a complete ecosystem for JSON processing, including serialization and deserialization
- JsonPath is more lightweight and easier to use for simple JSON querying tasks
- Jackson offers more flexibility and control over JSON handling, making it suitable for complex use cases
Both libraries have their strengths, and the choice depends on the specific requirements of your project. JsonPath is ideal for simple JSON querying, while Jackson excels in comprehensive JSON processing scenarios.
A Java serialization/deserialization library to convert Java Objects into JSON and back
Pros of Gson
- Full-featured JSON serialization/deserialization library
- Supports custom type adapters for complex objects
- Widely adopted and well-maintained by Google
Cons of Gson
- Steeper learning curve for advanced features
- Requires more boilerplate code for simple operations
- Less focused on JSON querying/manipulation
Code Comparison
JsonPath:
String json = "{\"store\":{\"book\":[{\"title\":\"Sayings of the Century\"}]}}";
String title = JsonPath.read(json, "$.store.book[0].title");
Gson:
String json = "{\"store\":{\"book\":[{\"title\":\"Sayings of the Century\"}]}}";
JsonObject jsonObject = JsonParser.parseString(json).getAsJsonObject();
String title = jsonObject.getAsJsonObject("store")
.getAsJsonArray("book")
.get(0).getAsJsonObject()
.get("title").getAsString();
Key Differences
- JsonPath focuses on querying JSON using path expressions
- Gson is a more comprehensive JSON processing library
- JsonPath offers a more concise syntax for extracting data
- Gson provides better support for object mapping and custom serialization
Use Cases
- Choose JsonPath for simple JSON querying and data extraction
- Opt for Gson when working with complex object serialization/deserialization or when deeper integration with Java objects is required
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Jayway JsonPath
A Java DSL for reading JSON documents.
Jayway JsonPath is a Java port of Stefan Goessner JsonPath implementation.
Getting Started
JsonPath is available at the Central Maven Repository. Maven users add this to your POM.
<dependency>
<groupId>com.jayway.jsonpath</groupId>
<artifactId>json-path</artifactId>
<version>2.9.0</version>
</dependency>
If you need help ask questions at Stack Overflow. Tag the question 'jsonpath' and 'java'.
JsonPath expressions always refer to a JSON structure in the same way as XPath expression are used in combination
with an XML document. The "root member object" in JsonPath is always referred to as $
regardless if it is an
object or array.
JsonPath expressions can use the dotânotation
$.store.book[0].title
or the bracketânotation
$['store']['book'][0]['title']
Operators
Operator | Description |
---|---|
$ | The root element to query. This starts all path expressions. |
@ | The current node being processed by a filter predicate. |
* | Wildcard. Available anywhere a name or numeric are required. |
.. | Deep scan. Available anywhere a name is required. |
.<name> | Dot-notated child |
['<name>' (, '<name>')] | Bracket-notated child or children |
[<number> (, <number>)] | Array index or indexes |
[start:end] | Array slice operator |
[?(<expression>)] | Filter expression. Expression must evaluate to a boolean value. |
Functions
Functions can be invoked at the tail end of a path - the input to a function is the output of the path expression. The function output is dictated by the function itself.
Function | Description | Output type |
---|---|---|
min() | Provides the min value of an array of numbers | Double |
max() | Provides the max value of an array of numbers | Double |
avg() | Provides the average value of an array of numbers | Double |
stddev() | Provides the standard deviation value of an array of numbers | Double |
length() | Provides the length of an array | Integer |
sum() | Provides the sum value of an array of numbers | Double |
keys() | Provides the property keys (An alternative for terminal tilde ~ ) | Set<E> |
concat(X) | Provides a concatinated version of the path output with a new item | like input |
append(X) | add an item to the json path output array | like input |
first() | Provides the first item of an array | Depends on the array |
last() | Provides the last item of an array | Depends on the array |
index(X) | Provides the item of an array of index: X, if the X is negative, take from backwards | Depends on the array |
Filter Operators
Filters are logical expressions used to filter arrays. A typical filter would be [?(@.age > 18)]
where @
represents the current item being processed. More complex filters can be created with logical operators &&
and ||
. String literals must be enclosed by single or double quotes ([?(@.color == 'blue')]
or [?(@.color == "blue")]
).
Operator | Description |
---|---|
== | left is equal to right (note that 1 is not equal to '1') |
!= | left is not equal to right |
< | left is less than right |
<= | left is less or equal to right |
> | left is greater than right |
>= | left is greater than or equal to right |
=~ | left matches regular expression [?(@.name =~ /foo.*?/i)] |
in | left exists in right [?(@.size in ['S', 'M'])] |
nin | left does not exists in right |
subsetof | left is a subset of right [?(@.sizes subsetof ['S', 'M', 'L'])] |
anyof | left has an intersection with right [?(@.sizes anyof ['M', 'L'])] |
noneof | left has no intersection with right [?(@.sizes noneof ['M', 'L'])] |
size | size of left (array or string) should match right |
empty | left (array or string) should be empty |
Path Examples
Given the json
{
"store": {
"book": [
{
"category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
},
{
"category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
},
{
"category": "fiction",
"author": "Herman Melville",
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"price": 8.99
},
{
"category": "fiction",
"author": "J. R. R. Tolkien",
"title": "The Lord of the Rings",
"isbn": "0-395-19395-8",
"price": 22.99
}
],
"bicycle": {
"color": "red",
"price": 19.95
}
},
"expensive": 10
}
JsonPath | Result |
---|---|
$.store.book[*].author | The authors of all books |
$..author | All authors |
$.store.* | All things, both books and bicycles |
$.store..price | The price of everything |
$..book[2] | The third book |
$..book[-2] | The second to last book |
$..book[0,1] | The first two books |
$..book[:2] | All books from index 0 (inclusive) until index 2 (exclusive) |
$..book[1:2] | All books from index 1 (inclusive) until index 2 (exclusive) |
$..book[-2:] | Last two books |
$..book[2:] | All books from index 2 (inclusive) to last |
$..book[?(@.isbn)] | All books with an ISBN number |
$.store.book[?(@.price < 10)] | All books in store cheaper than 10 |
$..book[?(@.price <= $['expensive'])] | All books in store that are not "expensive" |
$..book[?(@.author =~ /.*REES/i)] | All books matching regex (ignore case) |
$..* | Give me every thing |
$..book.length() | The number of books |
Reading a Document
The simplest most straight forward way to use JsonPath is via the static read API.
String json = "...";
List<String> authors = JsonPath.read(json, "$.store.book[*].author");
If you only want to read once this is OK. In case you need to read an other path as well this is not the way to go since the document will be parsed every time you call JsonPath.read(...). To avoid the problem you can parse the json first.
String json = "...";
Object document = Configuration.defaultConfiguration().jsonProvider().parse(json);
String author0 = JsonPath.read(document, "$.store.book[0].author");
String author1 = JsonPath.read(document, "$.store.book[1].author");
JsonPath also provides a fluent API. This is also the most flexible one.
String json = "...";
ReadContext ctx = JsonPath.parse(json);
List<String> authorsOfBooksWithISBN = ctx.read("$.store.book[?(@.isbn)].author");
List<Map<String, Object>> expensiveBooks = JsonPath
.using(configuration)
.parse(json)
.read("$.store.book[?(@.price > 10)]", List.class);
What is Returned When?
When using JsonPath in java its important to know what type you expect in your result. JsonPath will automatically try to cast the result to the type expected by the invoker.
//Will throw an java.lang.ClassCastException
List<String> list = JsonPath.parse(json).read("$.store.book[0].author");
//Works fine
String author = JsonPath.parse(json).read("$.store.book[0].author");
When evaluating a path you need to understand the concept of when a path is definite
. A path is indefinite
if it contains:
..
- a deep scan operator?(<expression>)
- an expression[<number>, <number> (, <number>)]
- multiple array indexes
Indefinite
paths always returns a list (as represented by current JsonProvider).
By default a simple object mapper is provided by the MappingProvider SPI. This allows you to specify the return type you want and the MappingProvider will
try to perform the mapping. In the example below mapping between Long
and Date
is demonstrated.
String json = "{\"date_as_long\" : 1411455611975}";
Date date = JsonPath.parse(json).read("$['date_as_long']", Date.class);
If you configure JsonPath to use JacksonMappingProvider
, GsonMappingProvider
, or JakartaJsonProvider
you can even map your JsonPath output directly into POJO's.
Book book = JsonPath.parse(json).read("$.store.book[0]", Book.class);
To obtain full generics type information, use TypeRef.
TypeRef<List<String>> typeRef = new TypeRef<List<String>>() {};
List<String> titles = JsonPath.parse(JSON_DOCUMENT).read("$.store.book[*].title", typeRef);
Predicates
There are three different ways to create filter predicates in JsonPath.
Inline Predicates
Inline predicates are the ones defined in the path.
List<Map<String, Object>> books = JsonPath.parse(json)
.read("$.store.book[?(@.price < 10)]");
You can use &&
and ||
to combine multiple predicates [?(@.price < 10 && @.category == 'fiction')]
,
[?(@.category == 'reference' || @.price > 10)]
.
You can use !
to negate a predicate [?(!(@.price < 10 && @.category == 'fiction'))]
.
Filter Predicates
Predicates can be built using the Filter API as shown below:
import static com.jayway.jsonpath.JsonPath.parse;
import static com.jayway.jsonpath.Criteria.where;
import static com.jayway.jsonpath.Filter.filter;
...
...
Filter cheapFictionFilter = filter(
where("category").is("fiction").and("price").lte(10D)
);
List<Map<String, Object>> books =
parse(json).read("$.store.book[?]", cheapFictionFilter);
Notice the placeholder ?
for the filter in the path. When multiple filters are provided they are applied in order where the number of placeholders must match
the number of provided filters. You can specify multiple predicate placeholders in one filter operation [?, ?]
, both predicates must match.
Filters can also be combined with 'OR' and 'AND'
Filter fooOrBar = filter(
where("foo").exists(true)).or(where("bar").exists(true)
);
Filter fooAndBar = filter(
where("foo").exists(true)).and(where("bar").exists(true)
);
Roll Your Own
Third option is to implement your own predicates
Predicate booksWithISBN = new Predicate() {
@Override
public boolean apply(PredicateContext ctx) {
return ctx.item(Map.class).containsKey("isbn");
}
};
List<Map<String, Object>> books =
reader.read("$.store.book[?].isbn", List.class, booksWithISBN);
Path vs Value
In the Goessner implementation a JsonPath can return either Path
or Value
. Value
is the default and what all the examples above are returning. If you rather have the path of the elements our query is hitting this can be achieved with an option.
Configuration conf = Configuration.builder()
.options(Option.AS_PATH_LIST).build();
List<String> pathList = using(conf).parse(json).read("$..author");
assertThat(pathList).containsExactly(
"$['store']['book'][0]['author']",
"$['store']['book'][1]['author']",
"$['store']['book'][2]['author']",
"$['store']['book'][3]['author']");
Set a value
The library offers the possibility to set a value.
String newJson = JsonPath.parse(json).set("$['store']['book'][0]['author']", "Paul").jsonString();
Tweaking Configuration
Options
When creating your Configuration there are a few option flags that can alter the default behaviour.
DEFAULT_PATH_LEAF_TO_NULL
This option makes JsonPath return null for missing leafs. Consider the following json
[
{
"name" : "john",
"gender" : "male"
},
{
"name" : "ben"
}
]
Configuration conf = Configuration.defaultConfiguration();
//Works fine
String gender0 = JsonPath.using(conf).parse(json).read("$[0]['gender']");
//PathNotFoundException thrown
String gender1 = JsonPath.using(conf).parse(json).read("$[1]['gender']");
Configuration conf2 = conf.addOptions(Option.DEFAULT_PATH_LEAF_TO_NULL);
//Works fine
String gender0 = JsonPath.using(conf2).parse(json).read("$[0]['gender']");
//Works fine (null is returned)
String gender1 = JsonPath.using(conf2).parse(json).read("$[1]['gender']");
ALWAYS_RETURN_LIST
This option configures JsonPath to return a list even when the path is definite
.
Configuration conf = Configuration.defaultConfiguration();
//ClassCastException thrown
List<String> genders0 = JsonPath.using(conf).parse(json).read("$[0]['gender']");
Configuration conf2 = conf.addOptions(Option.ALWAYS_RETURN_LIST);
//Works fine
List<String> genders0 = JsonPath.using(conf2).parse(json).read("$[0]['gender']");
SUPPRESS_EXCEPTIONS
This option makes sure no exceptions are propagated from path evaluation. It follows these simple rules:
- If option
ALWAYS_RETURN_LIST
is present an empty list will be returned - If option
ALWAYS_RETURN_LIST
is NOT present null returned
REQUIRE_PROPERTIES
This option configures JsonPath to require properties defined in path when an indefinite
path is evaluated.
Configuration conf = Configuration.defaultConfiguration();
//Works fine
List<String> genders = JsonPath.using(conf).parse(json).read("$[*]['gender']");
Configuration conf2 = conf.addOptions(Option.REQUIRE_PROPERTIES);
//PathNotFoundException thrown
List<String> genders = JsonPath.using(conf2).parse(json).read("$[*]['gender']");
JsonProvider SPI
JsonPath is shipped with five different JsonProviders:
- JsonSmartJsonProvider (default)
- JacksonJsonProvider
- JacksonJsonNodeJsonProvider
- GsonJsonProvider
- JsonOrgJsonProvider
- JakartaJsonProvider
Changing the configuration defaults as demonstrated should only be done when your application is being initialized. Changes during runtime is strongly discouraged, especially in multi threaded applications.
Configuration.setDefaults(new Configuration.Defaults() {
private final JsonProvider jsonProvider = new JacksonJsonProvider();
private final MappingProvider mappingProvider = new JacksonMappingProvider();
@Override
public JsonProvider jsonProvider() {
return jsonProvider;
}
@Override
public MappingProvider mappingProvider() {
return mappingProvider;
}
@Override
public Set<Option> options() {
return EnumSet.noneOf(Option.class);
}
});
Note that the JacksonJsonProvider requires com.fasterxml.jackson.core:jackson-databind:2.4.5
and the GsonJsonProvider requires com.google.code.gson:gson:2.3.1
on your classpath.
Both of Jakarta EE 9 JSON-P (JSR-342) and JSON-B (JSR-367) providers expect at least Java 8 and require compatible JSON API implementations (such as Eclipse Glassfish and Eclipse Yasson) on application runtime classpath; such implementations may also be provided by Java EE application container. Please also note that Apache Johnzon is not classpath-compatible with Jakarta EE 9 specification yet, and if JSON-B mapping provider is chosen then JSON-P provider must be configured and used, too.
One peculiarity of Jakarta EE 9 specifications for JSON processing and databinding (mapping) is immutability of Json arrays and objects as soon as they are fully parsed or written to. To respect the API specification, but allow JsonPath to modify Json documents through add, set/put, replace, and delete operations, JakartaJsonProvider
has to be initiliazed with optional true
argument:
JsonProvider jsonProvider = new JakartaJsonProvider(true)
(enable mutable Json arrays and objects)JsonProvider jsonProvider = new JakartaJsonProvider()
(default, strict JSON-P API compliance)
All lookup and read operations with JsonPath are supported regardless of initilization mode. Default mode also needs less memory and is more performant.
Cache SPI
In JsonPath 2.1.0 a new Cache SPI was introduced. This allows API consumers to configure path caching in a way that suits their needs. The cache must be configured before it is accesses for the first time or a JsonPathException is thrown. JsonPath ships with two cache implementations
com.jayway.jsonpath.spi.cache.LRUCache
(default, thread safe)com.jayway.jsonpath.spi.cache.NOOPCache
(no cache)
If you want to implement your own cache the API is simple.
CacheProvider.setCache(new Cache() {
//Not thread safe simple cache
private Map<String, JsonPath> map = new HashMap<String, JsonPath>();
@Override
public JsonPath get(String key) {
return map.get(key);
}
@Override
public void put(String key, JsonPath jsonPath) {
map.put(key, jsonPath);
}
});
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