Create map or object with nested fields from properties file in Java

Question

I need to create JSON from Properties file with nested fields? For example, we have the following properties file:

student.name="John"
student.exam.math=5
teacher.skills=10

And I need the following JSON file on output:

Properties : {
    student : {
        name : "John",
        exam : {
            math : 5
        }
    },
    teacher : {
       skills : 10
    }
}

JSON code can be produced with FLEX-JSON Serializer or GSON libraries and this is not a problem. The main problem is to parse properties and produce Java Object or Map with nested properties. Is there any library allowing to do that? Thanks!

Andremoniy · Accepted Answer · 2019-08-28 05:29:58Z

AFAIK, there are no well-known libraries for doing that. But you can do this in a trivial way:

 public String propertiesToJson(Properties p) {
    Map tree = new LinkedHashMap();

    for (String name : p.stringPropertyNames()) {
        String[] parts = name.split("\\.");
        Map nextTree = tree;
        for (int i = 0, partsLength = parts.length; i < partsLength; i++) {
            String part = parts[i];
            Object v = nextTree.get(part);
            if (v == null) {
                if (i < partsLength - 1) {
                    Map newNextTree = new LinkedHashMap();
                    nextTree.put(part, newNextTree);
                    nextTree = newNextTree;
                } else {
                    nextTree.put(part, p.getProperty(name));
                }
            } else {
                if (i < partsLength - 1) {
                    nextTree = (Map) v;
                }
            }
        }
    }


    StringBuilder sb = new StringBuilder();
    sb.append("Properties : {\n");
    recursive(tree, sb, 1);
    sb.append("}");

    return sb.toString();
}

private void recursive(Map tree, StringBuilder sb, int deep) {
    boolean first = true;
    for (Object key : tree.keySet()) {
        if (!first) sb.append(",\n");
        else first = false;
        for (int t = 0; t < deep; t++) sb.append("\t");
        sb.append(key + " : ");
        Object v = tree.get(key);
        if (v instanceof Map) {
            sb.append("{\n");
            recursive((Map) v, sb, deep+1);
            for (int t = 0; t < deep; t++) sb.append("\t");
            sb.append("}");
        } else {
            sb.append(v);
        }
    }
    sb.append("\n");
}

deveth0 · Accepted Answer · 2018-07-17 10:44:44Z

1

Even as this post is older, a quite easy solution is the usage of the Jackson JavaPropsMapper:

flatMessages = ...;
JavaPropsMapper mapper = new JavaPropsMapper();
Map ret = mapper.readPropertiesAs(flatMessages, HashMap.class);

answered Jul 17, 2018 at 10:44

deveth0

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