JsonReader

JsonReader.cls

  public class JsonReader {
    public Map<String, Object> jsonMap {get; set;}

    public JsonReader(Map<String, Object> jsonMap) {
        this.jsonMap = jsonMap;
    }

    public String getString(String path) {
        return (String)getFieldAtPath(path);
    }

    public Double getDouble(String path) {
        return (Double)getFieldAtPath(path);
    }

    public Object getFieldAtPath(String path) {
        String[] pathParts = path.split('\\.');
        if (pathParts.size() == 0) {
            return jsonMap.get(path);
        }

        Object jsonTemp = jsonMap;
        for (Integer i = 0; i < pathParts.size() - 1; i++) {
            String part = pathParts[i];
            if (part.endsWith(']')) {
                jsonTemp = getFieldWithIndex(jsonTemp, part);
            } else {
                jsonTemp = ((Map<String, Object>)jsonTemp).get(part);
            }
        }

        String finalPath = pathParts[pathParts.size() - 1];
        if (finalPath.endsWith(']')) {
            return getFieldWithIndex(jsonTemp, finalPath);
        } else {
            return ((Map<String, Object>)jsonTemp).get(finalPath);
        }
    }

    private Object getFieldWithIndex(Object jsonTemp, String pathPart) {
        String[] partWithIndices = pathPart.split('\\[');
        String part = partWithIndices.remove(0);
        Object tempResult = ((Map<String, Object>)jsonTemp).get(part);
        for (String indexStr : partWithIndices) {
            Integer idx = Integer.valueOf(indexStr.removeEnd(']'));
            tempResult = ((Object[])tempResult).get(idx);
        }
        return tempResult;
    }
}

JsonReaderTest.cls

@IsTest(isParallel =true)
public class JsonReaderTest {
    @IsTest
    static void it_should_get_field_as_string() {
        Map<String, Object> jsonMap = new Map<String, Object> {
            'id' => '123',
            'data' => new Map<String, Object> {
                'name' => 'steve',
                'address' => new Map<String, Object> {
                    'line1' => '123 Sesame St'
                }
            }
        };

        JsonReader jsonReader = new JsonReader(jsonMap);

        System.assertEquals('123', jsonReader.getString('id'));
        System.assertEquals('steve', jsonReader.getString('data.name'));
        System.assertEquals('123 Sesame St', jsonReader.getString('data.address.line1'));
        System.assertEquals(null, jsonReader.getString('data.address.line2'));
    }

    @IsTest
    static void it_should_get_field_as_double() {
        Map<String, Object> jsonMap = new Map<String, Object> {
            'id' => 123,
            'data' => new Map<String, Object> {
                'name' => 45.6,
                'address' => new Map<String, Object> {
                    'line1' => null
                }
            }
        };

        JsonReader jsonReader = new JsonReader(jsonMap);

        System.assertEquals(123, jsonReader.getDouble('id'));
        System.assertEquals(45.6, jsonReader.getDouble('data.name'));
        System.assertEquals(null, jsonReader.getDouble('data.address.line1'));
    }

    @IsTest
    static void it_should_get_array_field_as_string() {
        Map<String, Object> jsonMap = new Map<String, Object> {
            'test1' => new Object[] {
                1, 2, 3
            },
            'test2' => new Object[] {
                new Object[] {
                    1, 2, 3
                },
                new Object[] {
                    4, 5, 6
                }
            },
            'test3' => new Object[] {
                new Map<String, Object> {
                    'name' => 'seadog'
                }
            }
        };

        JsonReader jsonReader = new JsonReader(jsonMap);
        System.assertEquals(1, jsonReader.getDouble('test1[0]'));
        System.assertEquals(6, jsonReader.getDouble('test2[1][2]'));
        System.assertEquals('seadog', jsonReader.getString('test3[0].name'));
    }
}