當我試圖在安卓

我想寫我modelclass數據轉換成JSON文件將數據寫入文件，這裏是我的代碼當我試圖在安卓

activity_main.xml中

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    android:orientation="vertical" 
    android:padding="5dp" 
    tools:context=".MainActivity"> 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:textAppearance="?android:attr/textAppearanceMedium" 
     android:text="Name:" 
     android:textSize="21dp" 
     android:id="@+id/txtName" /> 

    <EditText 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/editName" 
     android:hint="Name" 
     android:paddingLeft="10dp" 
     android:textColorHint="@color/colorAccent"/> 
    <View 
     android:layout_width="wrap_content" 
     android:layout_height="25dp"></View> 
    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:textAppearance="?android:attr/textAppearanceMedium" 
     android:text="City:" 
     android:textSize="21dp" 
     android:id="@+id/txtCity" /> 

    <EditText 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/editCity" 
     android:hint="City" 
     android:paddingLeft="10dp" 
     android:textColorHint="@color/colorAccent"/> 

    <View 
     android:layout_width="wrap_content" 
     android:layout_height="25dp"></View> 
    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:textAppearance="?android:attr/textAppearanceMedium" 
     android:text="Mobile:" 
     android:textSize="21dp" 
     android:id="@+id/txtMobile" /> 

    <EditText 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:inputType="phone" 
     android:ems="10" 
     android:paddingLeft="10dp" 
     android:id="@+id/editMobile" 
     android:hint="Mobile" 
     android:textColorHint="@color/colorAccent"/> 

    <View 
     android:layout_width="wrap_content" 
     android:layout_height="25dp"></View> 

    <Button 
     android:id="@+id/btnInsert" 
     android:layout_width="match_parent" 
     android:layout_height="50dp" 
     android:textAlignment="center" 
     android:text="Insert" 
     android:textSize="21dp" 
     android:textColor="#FFFFFF" 
     android:background="@color/colorAccent"/> 
</LinearLayout>

在這裏，我的模型類，即學生。 java的

package model; 

import java.io.Serializable; 

/** 
* Created by MY WORLD on 11/26/15. 
*/ 
public class Student implements Serializable { 

    private int id; 
    private String name; 
    private String city; 
    private String phno; 

    public String getCity() { 
     return city; 
    } 

    public void setCity(String city) { 

     this.city = city; 
    } 

    public int getId() { 
     return id; 
    } 

    public void setId(int id) { 
     this.id = id; 
    } 

    public String getName() { 
     return name; 
    } 

    public void setName(String name) { 
     this.name = name; 
    } 

    public String getPhno() { 
     return phno; 
    } 

    public void setPhno(String phno) { 
     this.phno = phno; 
    } 

    @Override 
    public String toString() { 
     return "Student[id="+id+"name="+name+"city="+city+"phno="+phno+"]"; 
    } 
}

這裏是我的mainActivity.java

package com.domore.jsonserialization; 

import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 

import com.google.gson.Gson; 

import java.io.BufferedOutputStream; 
import java.io.BufferedWriter; 
import java.io.File; 
import java.io.FileNotFoundException; 
import java.io.FileOutputStream; 
import java.io.FileWriter; 
import java.io.IOException; 
import java.io.ObjectOutput; 
import java.io.ObjectOutputStream; 

import model.Student; 

public class MainActivity extends AppCompatActivity implements View.OnClickListener { 

    EditText name,city,mobile; 
    Button insert; 
    int id=1; 
    FileOutputStream fos=null; 
    BufferedOutputStream bos=null; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 


     name=(EditText)findViewById(R.id.editName); 
     city=(EditText)findViewById(R.id.editCity); 
     mobile=(EditText)findViewById(R.id.editMobile); 

     insert=(Button)findViewById(R.id.btnInsert); 

     insert.setOnClickListener(this); 
    } 
    @Override 
    public void onClick(View v) { 

     Student std=new Student(); 
     std.setId(id); 
     std.setName(name.getText().toString()); 
     std.setCity(city.getText().toString()); 
     std.setPhno(mobile.getText().toString()); 

     Gson gson=new Gson(); 

     String json=gson.toJson(std); 

     Log.e("name:",std.getName()); 
     Log.e("json Data",""+json); 
     try{ 

      fos=new FileOutputStream("D:\\Student.json"); 
      byte b[]=json.getBytes(); 
      fos.write(b); 
      fos.close(); 
     } 
     catch (FileNotFoundException ffe){ 
      ffe.printStackTrace(); 
     } 
     catch(IOException e){ 
      e.printStackTrace(); 
     } 
     finally { 
      try{ 
       fos.close(); 
      } 
      catch (IOException e){ 
       e.printStackTrace(); 
      } 
     } 
    } 
}

我用了2錯誤，如下面

1錯誤

11-26 11:18:08.680 2608-2608/? W/System.err: java.io.FileNotFoundException: D:\Student.json: open failed: EROFS (Read-only file system) 
11-26 11:18:08.680 2608-2608/? W/System.err:  at libcore.io.IoBridge.open(IoBridge.java:456) 
11-26 11:18:08.680 2608-2608/? W/System.err:  at java.io.FileOutputStream.<init>(FileOutputStream.java:87) 
11-26 11:18:08.680 2608-2608/? W/System.err:  at java.io.FileOutputStream.<init>(FileOutputStream.java:127) 
11-26 11:18:08.680 2608-2608/? W/System.err:  at java.io.FileOutputStream.<init>(FileOutputStream.java:116) 
11-26 11:18:08.681 2608-2608/? W/System.err:  at com.domore.jsonserialization.MainActivity.onClick(MainActivity.java:63)

第二個錯誤

FATAL EXCEPTION: main 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime: Process: com.domore.jsonserialization, PID: 2608 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.FileOutputStream.close()' on a null object reference 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime:  at com.domore.jsonserialization.MainActivity.onClick(MainActivity.java:76) 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime:  at android.view.View.performClick(View.java:4756) 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime:  at android.view.View$PerformClick.run(View.java:19749) 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime:  at android.os.Handler.handleCallback(Handler.java:739) 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:95) 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:135) 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:5221) 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Native Method) 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:372) 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 
11-26 11:18:08.682 2608-2608/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 
11-26 11:18:08.695 1238-1252/? W/ActivityManager: Force finishing activity com.domore.jsonserialization/.MainActivity

我該怎麼辦，請，建議我解決了這個錯誤

來源

2015-11-26 Millu

問題標題可以更好。 –

這就是你如何讀寫文件

首先，獲取文件對象

你需要的存儲路徑。對於內部存儲，使用方法：

File path = context.getFilesDir();

對於外部存儲（SD卡），使用：

File path = context.getExternalFilesDir(null);

然後創建您的文件對象：

File file = new File(path, "my-file-name.txt");

一個字符串寫入文件

FileOutputStream stream = new FileOutputStream(file); 
try { 
    stream.write("text-to-write".getBytes()); 
} finally { 
    stream.close(); 
}

或者與谷歌番石榴

Files.write("text-to-write", file, "UTF-8");

讀取文件爲一個字符串

int length = (int) file.length(); 

byte[] bytes = new byte[length]; 

FileInputStream in = new FileInputStream(file); 
try { 
    in.read(bytes); 
} finally { 
    in.close(); 
} 

String contents = new String(bytes);

或者，如果您使用的是谷歌番石榴

String contents = Files.toString(file,"UTF-8");

爲了完整性我會提到

String contents = new Scanner(file).useDelimiter("\\A").next();

不需要庫，但基準比其他選項慢50％ - 400％（在Nexus 5的各種測試中）。

注意

對於每一種策略，你會被要求趕上一個IOException。

Android上的默認字符編碼是UTF-8。

如果您正在使用外部存儲，你需要添加到您的清單之一：

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

或

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

寫權限意味着讀權限，所以你不需要兩個。

來源

2015-11-26 06:24:11

當我試圖在安卓

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