使用GSON在Android Studio中从文件读取JSON。

huangapple
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英文:

Reading JSON from file using GSON in Android Studio

问题

  1. fis = openFileInput(filename);
  3. BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
  5. StringBuilder data = new StringBuilder();
  6. String line = null;
  8. line = reader.readLine();
  10. while (line != null)
  11. {
  12.      data.append(line).append("\n");
  13. }
  15. data.toString();
  17. reader.close();
  18. fis.close();
  20. Type walletListType = new TypeToken<ArrayList<WalletClass>>(){}.getType();
  21. walletList.add(new Gson().fromJson(data.toString(), walletListType));

However, I'm getting the error

Cannot resolve method fromJson('java.lang.stringBuilder,
java.lang.reflect.Type')

The JSON I'm trying to load is (it's inside the square brackets because I've serialized it from a list of objects):

  1. [
  2.    {"balance":258,"walletName":"wallet 1"},
  3.    {"balance":5222,"walletName":"wallet 2"},
  4.    {"balance":1,"walletName":"wallet 3"}
  5. ]

I know a common fix for this is changing the import code from org to com, however, I've already made sure it is com.

英文:

I'm trying to read JSON from an internal storage file into a list of objects.

My code for reading the file and GSON is:

  1. fis = openFileInput(filename);
  3. BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
  5. StringBuilder data = new StringBuilder();
  6. String line = null;
  8. line = reader.readLine();
  10. while (line != null)
  11. {
  12.      data.append(line).append(&quot;\n&quot;);
  13. }
  15. data.toString();
  17. reader.close();
  18. fis.close();
  20. Type walletListType = new TypeToken&lt;ArrayList&lt;WalletClass&gt;&gt;(){}.getType();
  21. walletList.add(new Gson().fromJson(data, walletListType));

However, I'm getting the error

> Cannot resolve method fromJson('java.lang.stringBuilder,
> java.lang.reflect.Type')

The JSON I'm trying to load is (it's inside the square brackets because I've serialized it from a list of objects):

  1. [
  2.    {&quot;balance&quot;:258,&quot;walletName&quot;:&quot;wallet 1&quot;},
  3.    {&quot;balance&quot;:5222,&quot;walletName&quot;:&quot;wallet 2&quot;},
  4.    {&quot;balance&quot;:1,&quot;walletName&quot;:&quot;wallet 3&quot;}
  5. ]

I know a common fix for this is changing the import code from org to com, however I've already made sure it is com.

答案1

得分: 1

以下是翻译好的部分：

the Gson提供了许多fromJson方法的重载，以下是它们的签名：

使用GSON在Android Studio中从文件读取JSON。

但是正如你所见，它们中没有任何一个将StringBuilder作为第一个参数。这就是编译器所抱怨的内容。相反，你有一些以String作为第一个参数的构造函数。

因此，将这行代码：

  1. walletList.add(new Gson().fromJson(data, walletListType));

替换为：

  1. walletList.add(new Gson().fromJson(data.toString(), walletListType));

这样你应该就可以继续了。

英文:

the Gson provide a lot of overloads for the fromJson method, here are their signatures:

使用GSON在Android Studio中从文件读取JSON。

But as you can see none of them takes the StringBuilder as first argument. That is what the compiler is complaining about. Instead you have constructors that take a String as first argument.

So replace this line:

  1. walletList.add(new Gson().fromJson(data, walletListType));

with:

  1. walletList.add(new Gson().fromJson(data.toString(), walletListType));

And you should be good to go.

答案2

得分: 0

  1. 你可以使用GSON的类型适配器(Type adapter)来读写文件。
  2. 我已经用Kotlin写了这部分代码，希望能对你有所帮助。
  4. ```kotlin
  5. val builder = GsonBuilder()
  6.       builder.registerTypeAdapter(YourData::class.java, MyTypeAdapter())
  7.       return builder.create()

示例类型适配器(Type Adapter)

  1. class MyTypeAdapter : TypeAdapter<YourData>() {
  3.   @Throws(IOException::class)
  4.   override fun read(reader: JsonReader): YourData {
  5.     var element1
  6.     var element2
  7.     reader.beginObject()
  8.     while (reader.hasNext()) {
  9.       when (reader.nextName()) {
  10.         "element1" -> latitude = reader.nextDouble()
  11.         "element2" -> dropMessage = reader.nextString()
  12.       }
  13.     }
  14.     reader.endObject()
  16.     return YourData(element1, element2)
  17.   }
  19.   @Throws(IOException::class)
  20.   override fun write(out: JsonWriter, yourData: YourData) {
  21.     out.beginObject()
  22.     out.name("element1").value(yourData)
  23.     out.name("element2").value(yourData)
  24.     out.endObject()
  25.   }
  26. }

使用示例（读取和写入）

  1. fun saveData(yourData: YourData) {
  2.     val string = gson.toJson(yourData)
  3.     try {
  4.       val dataStream = dataOutputStream(yourData)
  5.       yourStream.write(string.toByteArray())
  6.       yourStream.close()
  7.     } catch (e: IOException) {
  8.       Log.e("FileRepository", "Error")
  9.     }
  10. }
  12. fun getData(): List<YourData> {
  13.     val data = mutableListOf<YourData>()
  15.     try {
  16.       val fileList = dataDirectory().list()
  18.       fileList.map { convertStreamToString(YourDataInputStream(it)) }.mapTo(data) {
  19.         gson.fromJson(it, YourData::class.java)
  20.       }
  21.     } catch (e: IOException) {
  22.       Log.e("FileRepository", "Error")
  23.     }
  25.     return data
  26. }
  2. <details>
  3. <summary>英文:</summary>
  5. You can use GSON&#39;s Type adapter to read and write files.
  6. I have written this in kotlin, I hope it helps you.

val builder = GsonBuilder()
builder.registerTypeAdapter(YourData::class.java, MyTypeAdapter())
return builder.create()

  2. Sample Type Adapter

class MyTypeAdapter : TypeAdapter<YourData>() {

@Throws(IOException::class)
override fun read(reader: JsonReader): YourData {
var element1
var element2
reader.beginObject()
while (reader.hasNext()) {
when (reader.nextName()) {
"element1" -> latitude = reader.nextDouble()
"element2" -> dropMessage = reader.nextString()
}
}
reader.endObject()

  1. return YourData(element1, element2)

}

@Throws(IOException::class)
override fun write(out: JsonWriter, yourData: YourData) {
out.beginObject()
out.name("element1").value(yourData)
out.name("element2").value(yourData)
out.endObject()
}
}

  1. Usage (Read &amp; Write)

fun saveData(yourData: YourData) {
val string = gson.toJson(yourData)
try {
val dataStream = dataOutputStream(yourData)
yourStream.write(string.toByteArray())
yourStream.close()
} catch (e: IOException) {
Log.e("FileRepository", "Error")
}
}

fun getData(): List<YourData> {
val data = mutableListOf<YourData>()

  1. try {
  2.   val fileList = dataDirectory().list()
  4.   fileList.map { convertStreamToString(YourDataInputStream(it)) }.mapTo(data) {
  5.     gson.fromJson(it, YourData::class.java)
  6.   }
  7. } catch (e: IOException) {
  8.   Log.e(&quot;FileRepository&quot;, &quot;Error&quot;)
  9. }
  11. return data

}

  2. </details>

huangapple
  • 本文由 发表于 2020年3月17日 00:47:11
  • 转载请务必保留本文链接：https://go.coder-hub.com/60709964.html
  • android
  • android-studio
  • gson
  • java
  • json
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