How to convert a JSON string to a Map<String, String> with Jackson JSON
[Update Sept 2020] Although my original answer here, from many years ago, seems to be helpful and is still getting upvotes, I now use the GSON library from Google, which I find to be more intuitive.
I've got the following code:
public void testJackson() throws IOException {
ObjectMapper mapper = new ObjectMapper();
File from = new File("albumnList.txt");
TypeReference<HashMap<String,Object>> typeRef
= new TypeReference<HashMap<String,Object>>() {};
HashMap<String,Object> o = mapper.readValue(from, typeRef);
System.out.println("Got " + o);
}
It's reading from a file, but mapper.readValue()
will also accept an InputStream
and you can obtain an InputStream
from a string by using the following:
new ByteArrayInputStream(astring.getBytes("UTF-8"));
There's a bit more explanation about the mapper on my blog.
Try TypeFactory
. Here's the code for Jackson JSON (2.8.4).
Map<String, String> result;
ObjectMapper mapper;
TypeFactory factory;
MapType type;
factory = TypeFactory.defaultInstance();
type = factory.constructMapType(HashMap.class, String.class, String.class);
mapper = new ObjectMapper();
result = mapper.readValue(data, type);
Here's the code for an older version of Jackson JSON.
Map<String, String> result = new ObjectMapper().readValue(
data, TypeFactory.mapType(HashMap.class, String.class, String.class));
Warning you get is done by compiler, not by library (or utility method).
Simplest way using Jackson directly would be:
HashMap<String,Object> props;
// src is a File, InputStream, String or such
props = new ObjectMapper().readValue(src, new TypeReference<HashMap<String,Object>>() {});
// or:
props = (HashMap<String,Object>) new ObjectMapper().readValue(src, HashMap.class);
// or even just:
@SuppressWarnings("unchecked") // suppresses typed/untype mismatch warnings, which is harmless
props = new ObjectMapper().readValue(src, HashMap.class);
Utility method you call probably just does something similar to this.