JsonPropertiesPersister for Spring

application-context.xml

	<bean id="placeholderConfig" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
		<property name="propertiesPersister">
			<bean class="JsonPropertiesPersister"></bean>
		</property>
		<property name="locations">
			<list>
				<value>classpath:public.json</value>
				<value>classpath:private.json</value>
			</list>
		</property>
		<property name="systemPropertiesModeName">
			<value>SYSTEM_PROPERTIES_MODE_OVERRIDE</value>
		</property>
	</bean>

JsonPropertiesPersister.java

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.Reader;
import java.io.Writer;
import java.util.Iterator;
import java.util.Map;
import java.util.Properties;

import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.map.ObjectMapper;
import org.springframework.util.PropertiesPersister;

public class JsonPropertiesPersister implements PropertiesPersister {
	@Override
	public void load(Properties props, InputStream is) throws IOException {
		load(props, new InputStreamReader(is));
	}

	@Override
	public void load(Properties props, Reader reader) throws IOException {
		ObjectMapper m = new ObjectMapper();
		m.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);
		m.configure(JsonParser.Feature.ALLOW_SINGLE_QUOTES, true);
		m.configure(JsonParser.Feature.ALLOW_COMMENTS, true);
		JsonNode node = m.readTree(reader);
		load(props, node, "");
	}
	
	void load(Properties props, JsonNode node, String key) {
		if (node.isObject()) {
			Iterator<Map.Entry<String, JsonNode>> fields = node.getFields();
			while (fields.hasNext()) {
				Map.Entry<String, JsonNode> field = fields.next();
				load(props, field.getValue(), join(key, field.getKey()));
			}
		} else if (node.isArray()) {
			Iterator<JsonNode> values = node.getElements();
			int i = 0;
			while (values.hasNext()) {
				JsonNode value = values.next();
				load(props, value, join(key, String.valueOf(i)));
				i++;
			}
		} else {
			props.setProperty(key, node.getValueAsText());
		}
	}
	
	String join(String prefix, String key) {
		return prefix.isEmpty() ? key : prefix + "." + key;
	}

	@Override
	public void store(Properties props, OutputStream os, String header) throws IOException {
		throw new UnsupportedOperationException();
	}

	@Override
	public void store(Properties props, Writer writer, String header) throws IOException {
		throw new UnsupportedOperationException();
	}

	@Override
	public void loadFromXml(Properties props, InputStream is) throws IOException {
		throw new UnsupportedOperationException();
	}

	@Override
	public void storeToXml(Properties props, OutputStream os, String header) throws IOException {
		throw new UnsupportedOperationException();
	}

	@Override
	public void storeToXml(Properties props, OutputStream os, String header, String encoding) throws IOException {
		throw new UnsupportedOperationException();
	}
}

JsonPropertiesPersisterTest.java

import java.io.IOException;
import java.io.StringReader;
import java.util.Properties;

import org.junit.Before;
import org.junit.Test;
import static org.hamcrest.Matchers.*;
import static org.junit.Assert.*;

public class JsonPropertiesPersisterTest {
	private JsonPropertiesPersister dut;
	private Properties props;

	@Before public void beforeEach() {
		dut = new JsonPropertiesPersister();
		props = new Properties();
	}
	
	@Test public void empty() throws IOException {
		dut.load(props, new StringReader("{}"));
		assertThat(props.isEmpty(), is(true));
	}

	@Test public void stringValue() throws IOException {
		dut.load(props, new StringReader("{key:\"value\"}"));
		assertThat(props.getProperty("key"), is("value"));
	}

	@Test public void numberValue() throws IOException {
		dut.load(props, new StringReader("{key:123}"));
		assertThat(props.getProperty("key"), is("123"));
	}

	@Test public void booleanValue() throws IOException {
		dut.load(props, new StringReader("{key:true}"));
		assertThat(props.getProperty("key"), is("true"));
	}
	
	@Test public void array() throws IOException {
		dut.load(props, new StringReader("{key:['a','b']}"));
		assertThat(props.getProperty("key.0"), is("a"));
		assertThat(props.getProperty("key.1"), is("b"));
	}

	@Test public void object() throws IOException {
		dut.load(props, new StringReader("{key:{subKey:'value'}}"));
		assertThat(props.getProperty("key.subKey"), is("value"));
	}
}