一段时间后尝试 Android 开发，我试图从 FTP 下载一个 zip 文件，但即使在重复尝试后，当我尝试在 FileOutputStream 中写入文件时仍然出现 FileNotFound 异常。该文件显然存在于本地存储中，因为我打印了 2-3 次（请检查输出日志）
MainActivity.java
package com.example.myapplication;
import android.app.ProgressDialog;
import android.content.Context;
import android.os.Bundle;
import android.os.Environment;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import org.apache.commons.net.ftp.FTPFile;
import java.io.File;
public class MainActivity extends AppCompatActivity {
private static final String LOG_TAG = "";
Spinner drop;
Button btn;
String[] items;
FTPFile[] file;
ArrayAdapter adapter;
ProgressDialog mProgressDialog;
String dwnFile = "";
String localFilePath;
File localFile;
FTPOps ftp;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn = (Button) findViewById(R.id.button1);
drop = (Spinner) findViewById(R.id.spinner);
items = new String[]{"hello"};
String path = Environment.getExternalStorageDirectory().toString();
System.out.println("Path: " + path);
File directory = new File(path);
File[] files = directory.listFiles();
for (int i = 0; i < files.length; i++) {
System.out.println(files[i].getName());
}
items = new String[]{"Select the file", "01.zip", "04.zip", "05.zip", "06.zip", "07.zip", "08.zip", "09.zip",};
adapter = new ArrayAdapter(this, android.R.layout.simple_spinner_dropdown_item, items);
drop.setAdapter(adapter);
btn.setOnClickListener(v -> {
dwnFile = drop.getSelectedItem().toString().equals("Select the file") ? "" : drop.getSelectedItem().toString();
if (dwnFile != "") {
Context context = this;
localFilePath = Environment.getExternalStorageDirectory() + "/" + "ebooks";
localFile = new File(localFilePath + "/" + dwnFile);
System.out.println(localFile.mkdir() ? "File created" : "Not created file");
if (localFile.exists()) {
System.out.println("File created");
} else {
System.out.println("File edxists already");
}
System.out.println(localFile.getPath());
Toast toast = Toast.makeText(getApplicationContext(), "Downloading...", Toast.LENGTH_LONG);
toast.show();
ftp = new FTPOps(localFile, context, dwnFile);
String msg = (ftp.runDownloadAndUnziping()) ? "Downloaded" : "Error in downloding";
toast = Toast.makeText(getApplicationContext(), msg, Toast.LENGTH_LONG);
toast.show();
}
});
}
}
Mainactivity 提供一个下拉菜单，可从文件列表中进行选择，并将数据发送到另一个类以供 FTP 下载。
FTPOps.java
package com.example.myapplication;
import android.content.Context;
import android.widget.Toast;
import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class FTPOps {
File localFile;
Context context;
FTPClient ftp;
String fileName;
public FTPOps(File localFile, Context context, String dwnFile) {
this.localFile = localFile;
this.context = context;
ftp = new FTPClient();
this.fileName = dwnFile;
}
public boolean runDownloadAndUnziping() {
setUpFTP();
return true;
}
private void setUpFTP() {
Thread t = new Thread(new Runnable() {
@Override
public void run() {
try {
ftp.connect("some$$$$url");
ftp.login("someID", "somePassword");
showToast("Login into FTP Successful");
ftp.enterLocalPassiveMode();
ftp.setFileType(FTP.BINARY_FILE_TYPE);
System.out.println("Downlaod in progress for " + fileName);
System.out.println("Local file is " + localFile.getPath());
FileOutputStream fo = new FileOutputStream(localFile.getPath());
if (fo == null) {
System.out.println("fo is null");
}
boolean r = ftp.retrieveFile(fileName, fo);
if (r) {
System.out.println("Operation success");
}
fo.close();
} catch (IOException e) {
e.printStackTrace();
showToast("Login Failed");
}
}
private void showToast(String msg) {
System.out.println(msg);
}
});
t.start();
}
}
我的输出日志：
06/13 01:13:00: Launching 'app' on Nexus 6 API 30.
Install successfully finished in 1 s 683 ms.
$ adb shell am start -n "com.example.myapplication/com.example.myapplication.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
Connected to process 13263 on device 'emulator-5554'.
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
D/NetworkSecurityConfig: No Network Security Config specified, using platform default
D/NetworkSecurityConfig: No Network Security Config specified, using platform default
D/libEGL: loaded /vendor/lib/egl/libEGL_emulation.so
D/libEGL: loaded /vendor/lib/egl/libGLESv1_CM_emulation.so
D/libEGL: loaded /vendor/lib/egl/libGLESv2_emulation.so
W/e.myapplicatio: Accessing hidden method Landroid/view/View;->computeFitSystemWindows(Landroid/graphics/Rect;Landroid/graphics/Rect;)Z (greylist, reflection, allowed)
W/e.myapplicatio: Accessing hidden method Landroid/view/ViewGroup;->makeOptionalFitsSystemWindows()V (greylist, reflection, allowed)
I/System.out: Path: /storage/emulated/0
I/System.out: Android
Music
Podcasts
Ringtones
Alarms
Notifications
Pictures
Movies
I/System.out: Download
DCIM
Audiobooks
Documents
D/HostConnection: HostConnection::get() New Host Connection established 0xf24e9f30, tid 13290
D/HostConnection: HostComposition ext ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_native_sync_v2 ANDROID_EMU_native_sync_v3 ANDROID_EMU_native_sync_v4 ANDROID_EMU_dma_v1 ANDROID_EMU_direct_mem ANDROID_EMU_host_composition_v1 ANDROID_EMU_host_composition_v2 ANDROID_EMU_vulkan ANDROID_EMU_deferred_vulkan_commands ANDROID_EMU_vulkan_null_optional_strings ANDROID_EMU_vulkan_create_resources_with_requirements ANDROID_EMU_YUV_Cache ANDROID_EMU_async_unmap_buffer ANDROID_EMU_vulkan_ignored_handles ANDROID_EMU_vulkan_free_memory_sync ANDROID_EMU_vulkan_shader_float16_int8 ANDROID_EMU_vulkan_async_queue_submit GL_OES_vertex_array_object GL_KHR_texture_compression_astc_ldr ANDROID_EMU_host_side_tracing ANDROID_EMU_async_frame_commands ANDROID_EMU_gles_max_version_2
W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
D/EGL_emulation: eglCreateContext: 0xf24ead30: maj 2 min 0 rcv 2
D/EGL_emulation: eglMakeCurrent: 0xf24ead30: ver 2 0 (tinfo 0xf28370f0) (first time)
I/Gralloc4: mapper 4.x is not supported
D/HostConnection: createUnique: call
D/HostConnection: HostConnection::get() New Host Connection established 0xf24ea390, tid 13290
D/goldfish-address-space: allocate: Ask for block of size 0x100
D/goldfish-address-space: allocate: ioctl allocate returned offset 0x3f9d95000 size 0x2000
D/HostConnection: HostComposition ext ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_native_sync_v2 ANDROID_EMU_native_sync_v3 ANDROID_EMU_native_sync_v4 ANDROID_EMU_dma_v1 ANDROID_EMU_direct_mem ANDROID_EMU_host_composition_v1 ANDROID_EMU_host_composition_v2 ANDROID_EMU_vulkan ANDROID_EMU_deferred_vulkan_commands ANDROID_EMU_vulkan_null_optional_strings ANDROID_EMU_vulkan_create_resources_with_requirements ANDROID_EMU_YUV_Cache ANDROID_EMU_async_unmap_buffer ANDROID_EMU_vulkan_ignored_handles ANDROID_EMU_vulkan_free_memory_sync ANDROID_EMU_vulkan_shader_float16_int8 ANDROID_EMU_vulkan_async_queue_submit GL_OES_vertex_array_object GL_KHR_texture_compression_astc_ldr ANDROID_EMU_host_side_tracing ANDROID_EMU_async_frame_commands ANDROID_EMU_gles_max_version_2
I/Choreographer: Skipped 40 frames! The application may be doing too much work on its main thread.
I/OpenGLRenderer: Davey! duration=760ms; Flags=0, IntendedVsync=24852661746550, Vsync=24853328413190, OldestInputEvent=9223372036854775807, NewestInputEvent=0, HandleInputStart=24853340948720, AnimationStart=24853340988320, PerformTraversalsStart=24853341581320, DrawStart=24853343717920, SyncQueued=24853344351620, SyncStart=24853344908520, IssueDrawCommandsStart=24853345141720, SwapBuffers=24853352646720, FrameCompleted=24853423084920, DequeueBufferDuration=981700, QueueBufferDuration=1455800, GpuCompleted=0,
W/e.myapplicatio: Accessing hidden field Landroid/widget/AbsListView;->mIsChildViewEnabled:Z (greylist, reflection, allowed)
D/OpenGLRenderer: endAllActiveAnimators on 0xec08c3d0 (DropDownListView) with handle 0xc3041870
I/System.out: Not created file
I/System.out: File edxists already
I/System.out: /storage/emulated/0/ebooks/06.zip
D/CompatibilityChangeReporter: Compat change id reported: 147798919; UID 10155; state: ENABLED
I/System.out: Login into FTP Successful
I/System.out: Downlaod in progress for 06.zip
***I/System.out: Local file is /storage/emulated/0/ebooks/06.zip***
**W/System.err: java.io.FileNotFoundException: /storage/emulated/0/ebooks/06.zip: open failed: ENOENT (No such file or directory)**
at libcore.io.IoBridge.open(IoBridge.java:492)
at java.io.FileOutputStream.<init>(FileOutputStream.java:236)
W/System.err: at java.io.FileOutputStream.<init>(FileOutputStream.java:125)
at com.example.myapplication.FTPOps$1.run(FTPOps.java:50)
at java.lang.Thread.run(Thread.java:923)
Caused by: android.system.ErrnoException: open failed: ENOENT (No such file or directory)
at libcore.io.Linux.open(Native Method)
W/System.err: at libcore.io.ForwardingOs.open(ForwardingOs.java:166)
at libcore.io.BlockGuardOs.open(BlockGuardOs.java:254)
W/System.err: at libcore.io.ForwardingOs.open(ForwardingOs.java:166)
at android.app.ActivityThread$AndroidOs.open(ActivityThread.java:7542)
W/System.err: at libcore.io.IoBridge.open(IoBridge.java:478)
... 4 more
I/System.out: Login Failed
我记得之前下载曾经是这样工作的，但我阅读了一些关于存储访问问题的帖子，所以我适当地更新了我的清单：
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE"/>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/Theme.MyApplication"
android:requestLegacyExternalStorage="true">
但结果是一样的。
现在我需要帮助理解：