How to convert a JSON string to a Map with Jackson JSON

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[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.

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