在 Android 应用程序资源中使用 JSON 文件

假设我在应用程序的原始资源文件夹中有一个包含 JSON 内容的文件。我如何将其读入应用程序，以便解析 JSON？

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From http://developer.android.com/guide/topics/resources/providing-resources.html:

raw/
Arbitrary files to save in their raw form. To open these resources with a raw InputStream, call Resources.openRawResource() with the resource ID, which is R.raw.filename.

However, if you need access to original file names and file hierarchy, you might consider saving some resources in the assets/ directory (instead of res/raw/). Files in assets/ are not given a resource ID, so you can read them only using AssetManager.

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最佳答案

See openRawResource. Something like this should work:

InputStream is = getResources().openRawResource(R.raw.json_file);
Writer writer = new StringWriter();
char[] buffer = new char[1024];
try {
Reader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
int n;
while ((n = reader.read(buffer)) != -1) {
writer.write(buffer, 0, n);
}
} finally {
is.close();
}


String jsonString = writer.toString();
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I used @kabuko's answer to create an object that loads from a JSON file, using Gson, from the Resources:

package com.jingit.mobile.testsupport;


import java.io.*;


import android.content.res.Resources;
import android.util.Log;


import com.google.gson.Gson;
import com.google.gson.GsonBuilder;




/**
* An object for reading from a JSON resource file and constructing an object from that resource file using Gson.
*/
public class JSONResourceReader {


// === [ Private Data Members ] ============================================


// Our JSON, in string form.
private String jsonString;
private static final String LOGTAG = JSONResourceReader.class.getSimpleName();


// === [ Public API ] ======================================================


/**
* Read from a resources file and create a {@link JSONResourceReader} object that will allow the creation of other
* objects from this resource.
*
* @param resources An application {@link Resources} object.
* @param id The id for the resource to load, typically held in the raw/ folder.
*/
public JSONResourceReader(Resources resources, int id) {
InputStream resourceReader = resources.openRawResource(id);
Writer writer = new StringWriter();
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(resourceReader, "UTF-8"));
String line = reader.readLine();
while (line != null) {
writer.write(line);
line = reader.readLine();
}
} catch (Exception e) {
Log.e(LOGTAG, "Unhandled exception while using JSONResourceReader", e);
} finally {
try {
resourceReader.close();
} catch (Exception e) {
Log.e(LOGTAG, "Unhandled exception while using JSONResourceReader", e);
}
}


jsonString = writer.toString();
}


/**
* Build an object from the specified JSON resource using Gson.
*
* @param type The type of the object to build.
*
* @return An object of type T, with member fields populated using Gson.
*/
public <T> T constructUsingGson(Class<T> type) {
Gson gson = new GsonBuilder().create();
return gson.fromJson(jsonString, type);
}
}

To use it, you'd do something like the following (the example is in an InstrumentationTestCase):

   @Override
public void setUp() {
// Load our JSON file.
JSONResourceReader reader = new JSONResourceReader(getInstrumentation().getContext().getResources(), R.raw.jsonfile);
MyJsonObject jsonObj = reader.constructUsingGson(MyJsonObject.class);
}
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InputStream is = mContext.getResources().openRawResource(R.raw.json_regions);
int size = is.available();
byte[] buffer = new byte[size];
is.read(buffer);
is.close();
String json = new String(buffer, "UTF-8");
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Kotlin is now official language for Android, so I think this would be useful for someone

val text = resources.openRawResource(R.raw.your_text_file)
.bufferedReader().use { it.readText() }
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Like @mah states, the Android documentation (https://developer.android.com/guide/topics/resources/providing-resources.html) says that json files may be saved in the /raw directory under the /res (resources) directory in your project, for example:

MyProject/
src/
MyActivity.java
res/
drawable/
graphic.png
layout/
main.xml
info.xml
mipmap/
icon.png
values/
strings.xml
raw/
myjsonfile.json

Inside an Activity, the json file can be accessed through the R (Resources) class, and read to a String:

Context context = this;
Inputstream inputStream = context.getResources().openRawResource(R.raw.myjsonfile);
String jsonString = new Scanner(inputStream).useDelimiter("\\A").next();

This uses the Java class Scanner, leading to less lines of code than some other methods of reading a simple text / json file. The delimiter pattern \A means 'the beginning of the input'. .next() reads the next token, which is the whole file in this case.

There are multiple ways to parse the resulting json string:

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Using:

String json_string = readRawResource(R.raw.json)

Functions:

public String readRawResource(@RawRes int res) {
return readStream(context.getResources().openRawResource(res));
}


private String readStream(InputStream is) {
Scanner s = new Scanner(is).useDelimiter("\\A");
return s.hasNext() ? s.next() : "";
}
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Found this Kotlin snippet answer very helpful ♥️

While the original question asked to get a JSON String, I figure some might find this useful. A step further with Gson leads to this little function with reified type:

private inline fun <reified T> readRawJson(@RawRes rawResId: Int): T {
resources.openRawResource(rawResId).bufferedReader().use {
return gson.fromJson<T>(it, object: TypeToken<T>() {}.type)
}
}

Note you want to use TypeToken not just T::class so if you read a List<YourType> you won't lose the type by type erasure.

With the type inference you can then use like this:

fun pricingData(): List<PricingData> = readRawJson(R.raw.mock_pricing_data)

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