Save a pojo to file

ILJsonCollectionFile.java

package com.instacart.library.persistence;

import android.content.Context;

import com.fasterxml.jackson.core.type.TypeReference;

import java.io.IOException;
import java.util.List;

public class ILJsonCollectionFile<PAYLOAD> extends ILJsonFile<List<PAYLOAD>> {

    private final String mTag;

    public ILJsonCollectionFile(Context context, String filename, String tag) {
        super(context, filename, tag);
        mTag = tag;
    }

    public void store(List<PAYLOAD> data) throws IOException {
        super.store(data);
    }

    public List<PAYLOAD> read() throws IOException {
        TypeReference<List<PAYLOAD>> typeReference = new TypeReference<List<PAYLOAD>>() { };
        return read(typeReference);
    }
}

ILJsonFile.java

package com.instacart.library.persistence;

import android.content.Context;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.instacart.library.ILLog;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.Type;

public class ILJsonFile<PAYLOAD> {

    private final Context mContext;
    private final String mFilename;
    private Class<PAYLOAD> mPayloadClass;
    private final String mTag;

    public ILJsonFile(Context context, String filename, String tag) {
        mContext = context;
        mFilename = filename;
        mTag = tag;
    }

    private ObjectMapper getObjectMapper() {
        ObjectMapper mapper = new ObjectMapper();
        mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
        mapper.configure(SerializationFeature.INDENT_OUTPUT, false);
        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        return mapper;
    }

    public ILJsonFile(Context context, String filename, String tag, Class<PAYLOAD> clazz) {
        this(context, filename, tag);
        mPayloadClass = clazz;
    }

    public void store(PAYLOAD data) throws IOException {
        ObjectMapper mapper = getObjectMapper();
        FileWriter writer = new FileWriter(getFile(), false);
        mapper.writeValue(writer, data);
        writer.close();
    }

    public PAYLOAD read() throws IOException {
        return read(new TypeReference<PAYLOAD>() {
            @Override public Type getType() {
                return mPayloadClass;
            }
        });
    }

    public PAYLOAD read(TypeReference<PAYLOAD> payloadClass) throws IOException {
        File file = getFile();
        try {
            ObjectMapper mapper = getObjectMapper();
            return mapper.readValue(file, payloadClass);
        } catch (JsonProcessingException jme) {
            ILLog.d(mTag, "failed reading application data", jme);
        } catch (FileNotFoundException fnf) {
            ;
        } catch (IOException io) {
            // if data is corrupt, get rid of it.
            file.delete();
            throw io;
        }
        return null;
    }

    public File getFile() {
        File cacheDir = mContext.getApplicationContext().getCacheDir();
        return new File(cacheDir, mFilename);
    }

    public String getTag() {
        return mTag;
    }

    public void delete() {
        getFile().delete();
    }
}