MINotes/BackupUtils.java

这段代码是一个Android应用程序中的一个工具类，用于将笔记数据备份到文本文件中。下面是对这段代码的逐行注释：

```java
/*
 * Copyright (c) 2010-2011, The MiCode Open Source Community (www.micode.net)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0 
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
// 版权声明，说明该代码遵循Apache License 2.0。

package net.micode.notes.tool;

// 导入所需的Android类库
import android.content.Context;
import android.database.Cursor;
import android.os.Environment;
import android.text.TextUtils;
import android.text.format.DateFormat;
import android.util.Log;

// 导入应用程序自定义的类和资源
import net.micode.notes.R;
import net.micode.notes.data.Notes;
import net.micode.notes.data.Notes.DataColumns;
import net.micode.notes.data.Notes.DataConstants;
import net.micode.notes.data.Notes.NoteColumns;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintStream;

// 定义BackupUtils类，用于备份笔记数据
public class BackupUtils {
    private static final String TAG = "BackupUtils";
    // 定义日志标签

    private static BackupUtils sInstance;
    // 单例模式，用于全局访问BackupUtils实例

    // 获取BackupUtils实例的方法
    public static synchronized BackupUtils getInstance(Context context) {
        if (sInstance == null) {
            sInstance = new BackupUtils(context);
        }
        return sInstance;
    }

    // 定义备份状态常量
    public static final int STATE_SD_CARD_UNMOUONTED = 0;
    public static final int STATE_BACKUP_FILE_NOT_EXIST = 1;
    public static final int STATE_DATA_DESTROIED = 2;
    public static final int STATE_SYSTEM_ERROR = 3;
    public static final int STATE_SUCCESS = 4;

    private TextExport mTextExport;
    // TextExport实例，用于将数据导出到文本

    // 私有构造方法，确保只能通过getInstance方法获取实例
    private BackupUtils(Context context) {
        mTextExport = new TextExport(context);
    }

    // 检查外部存储是否可用
    private static boolean externalStorageAvailable() {
        return Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState());
    }

    // 导出数据到文本的方法
    public int exportToText() {
        return mTextExport.exportToText();
    }

    // 获取导出文本文件的文件名
    public String getExportedTextFileName() {
        return mTextExport.mFileName;
    }

    // 获取导出文本文件的目录
    public String getExportedTextFileDir() {
        return mTextExport.mFileDirectory;
    }

    // TextExport内部类，用于将笔记数据导出到文本
    private static class TextExport {
        // 定义查询笔记数据的投影数组
        private static final String[] NOTE_PROJECTION = {
                NoteColumns.ID,
                NoteColumns.MODIFIED_DATE,
                NoteColumns.SNIPPET,
                NoteColumns.TYPE
        };

        // 定义投影数组的索引常量
        private static final int NOTE_COLUMN_ID = 0;
        private static final int NOTE_COLUMN_MODIFIED_DATE = 1;
        private static final int NOTE_COLUMN_SNIPPET = 2;

        // 定义查询数据的投影数组
        private static final String[] DATA_PROJECTION = {
                DataColumns.CONTENT,
                DataColumns.MIME_TYPE,
                DataColumns.DATA1,
                DataColumns.DATA2,
                DataColumns.DATA3,
                DataColumns.DATA4,
        };

        // 定义投影数组的索引常量
        private static final int DATA_COLUMN_CONTENT = 0;
        private static final int DATA_COLUMN_MIME_TYPE = 1;
        private static final int DATA_COLUMN_CALL_DATE = 2;
        private static final int DATA_COLUMN_PHONE_NUMBER = 4;

        // 定义文本格式数组
        private final String[] TEXT_FORMAT;
        private Context mContext;
        private String mFileName;
        private String mFileDirectory;

        // TextExport构造方法
        public TextExport(Context context) {
            TEXT_FORMAT = context.getResources().getStringArray(R.array.format_for_exported_note);
            mContext = context;
            mFileName = "";
            mFileDirectory = "";
        }

        // 获取文本格式的方法
        private String getFormat(int id) {
            return TEXT_FORMAT[id];
        }

        // 导出文件夹到文本的方法
        private void exportFolderToText(String folderId, PrintStream ps) {
            // 查询文件夹内笔记的数据
            Cursor notesCursor = mContext.getContentResolver().query(
                    Notes.CONTENT_NOTE_URI,
                    NOTE_PROJECTION,
                    NoteColumns.PARENT_ID + "=?", new String[] {
                        folderId
                    }, null);

            if (notesCursor != null) {
                if (notesCursor.moveToFirst()) {
                    do {
                        // 打印笔记的修改日期
                        ps.println(String.format(getFormat(FORMAT_NOTE_DATE), DateFormat.format(
                                mContext.getString(R.string.format_datetime_mdhm),
                                notesCursor.getLong(NOTE_COLUMN_MODIFIED_DATE))));
                        // 查询笔记的内容
                        String noteId = notesCursor.getString(NOTE_COLUMN_ID);
                        exportNoteToText(noteId, ps);
                    } while (notesCursor.moveToNext());
                }
                notesCursor.close();
            }
        }

        // 导出笔记到文本的方法
        private void exportNoteToText(String noteId, PrintStream ps) {
            // 查询笔记的内容
            Cursor dataCursor = mContext.getContentResolver().query(
                    Notes.CONTENT_DATA_URI,
                    DATA_PROJECTION,
                    DataColumns.NOTE_ID + "=?", new String[] {
                        noteId
                    }, null);

            if (dataCursor != null) {
                if (dataCursor.moveToFirst()) {
                    do {
                        String mimeType = dataCursor.getString(DATA_COLUMN_MIME_TYPE);
                        if (DataConstants.CALL_NOTE.equals(mimeType)) {
                            // 处理通话记录类型的笔记
                            String phoneNumber = dataCursor.getString(DATA_COLUMN_PHONE_NUMBER);
                            long callDate = dataCursor.getLong(DATA_COLUMN_CALL_DATE);
                            String location = dataCursor.getString(DATA_COLUMN_CONTENT);

                            if (!TextUtils.isEmpty(phoneNumber)) {
                                ps.println(String.format(getFormat(FORMAT_NOTE_CONTENT),
                                        phoneNumber));
                            }
                            // 打印通话日期
                            ps.println(String.format(getFormat(FORMAT_NOTE_CONTENT), DateFormat
                                    .format(mContext.getString(R.string.format_datetime_mdhm),
                                            callDate)));
                            // 打印通话地点
                            if (!TextUtils.isEmpty(location)) {
                                ps.println(String.format(getFormat(FORMAT_NOTE_CONTENT),
                                        location));
                            }
                        } else if (DataConstants.NOTE.equals(mimeType)) {
                            // 处理普通笔记
                            String content = dataCursor.getString(DATA_COLUMN_CONTENT);
                            if (!TextUtils.isEmpty(content)) {
                                ps.println(String.format(getFormat(FORMAT_NOTE_CONTENT),
                                        content));
                            }
                        }
                    } while (dataCursor.moveToNext());
                }
                dataCursor.close();
            }
            // 打印换行符
            try {
                ps.write(new byte[] {
                        Character.LINE_SEPARATOR, Character.LETTER_NUMBER
                });
            } catch (IOException e) {
                Log.e(TAG, e.toString());
            }
        }

        // 导出数据为文本文件的方法
        public int exportToText() {
            if (!externalStorageAvailable()) {
                Log.d(TAG, "Media was not mounted");
                return STATE_SD_CARD_UNMOUONTED;
            }

            PrintStream ps = getExportToTextPrintStream();
            if (ps == null) {
                Log.e(TAG, "get print stream error");
                return STATE_SYSTEM_ERROR;
            }
            // 查询所有文件夹和笔记的数据
            Cursor folderCursor = mContext.getContentResolver().query(
                    Notes.CONTENT_NOTE_URI,
                    NOTE_PROJECTION,
                    "(" + NoteColumns.TYPE + "=" + Notes.TYPE_FOLDER + " AND "
                            + NoteColumns.PARENT_ID + "<>" + Notes.ID_TRASH_FOLER + ") OR "
                            + NoteColumns.ID + "=" + Notes.ID_CALL_RECORD_FOLDER, null, null);

            if (folderCursor != null) {
                if (folderCursor.moveToFirst()) {
                    do {
                        // 打印文件夹名称
                        String folderName = "";
                        if (folderCursor.getLong(NOTE_COLUMN_ID) == Notes.ID_CALL_RECORD_FOLDER) {
                            folderName = mContext.getString(R.string.call_record_folder_name);
                        } else {
                            folderName = folderCursor.getString(NOTE_COLUMN_SNIPPET);
                        }
                        if (!TextUtils.isEmpty(folderName)) {
                            ps.println(String.format(getFormat(FORMAT_FOLDER_NAME), folderName));
                        }
                        String folderId = folderCursor.getString(NOTE_COLUMN_ID);
                        exportFolderToText(folderId, ps);
                    } while (folderCursor.moveToNext());
                }
                folderCursor.close();
            }

            // 打印笔记内容
            Cursor noteCursor = mContext.getContentResolver().query(
                    Notes.CONTENT_NOTE_URI,
                    NOTE_PROJECTION,
                    NoteColumns.TYPE + "=" + Notes.TYPE_NOTE + " AND " + NoteColumns.PARENT_ID
                            + "=0", null, null);

            if (noteCursor != null) {
            if (noteCursor.moveToFirst()) {
                do {
                    // 打印笔记的修改日期
                    ps.println(String.format(getFormat(FORMAT_NOTE_DATE), DateFormat.format(
                            mContext.getString(R.string.format_datetime_mdhm),
                            noteCursor.getLong(NOTE_COLUMN_MODIFIED_DATE))));
                    // 查询笔记的内容
                    String noteId = noteCursor.getString(NOTE_COLUMN_ID);
                    exportNoteToText(noteId, ps);
                } while (noteCursor.moveToNext());
            }
            noteCursor.close();
        }
        ps.close();

        return STATE_SUCCESS;
    }

    // 获取导出文本的PrintStream对象
    private PrintStream getExportToTextPrintStream() {
        // 创建文件
        File file = generateFileMountedOnSDcard(mContext, R.string.file_path,
                R.string.file_name_txt_format);
        if (file == null) {
            Log.e(TAG, "create file to exported failed");
            return null;
        }
        mFileName = file.getName();
        mFileDirectory = mContext.getString(R.string.file_path);
        PrintStream ps = null;
        try {
            FileOutputStream fos = new FileOutputStream(file);
            ps = new PrintStream(fos);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
            return null;
        } catch (NullPointerException e) {
            e.printStackTrace();
            return null;
        }
        return ps;
    }
}

// 在SD卡上生成文件的方法
private static File generateFileMountedOnSDcard(Context context, int filePathResId, int fileNameFormatResId) {
    StringBuilder sb = new StringBuilder();
    sb.append(Environment.getExternalStorageDirectory());
    sb.append(context.getString(filePathResId));
    File filedir = new File(sb.toString());

    // 创建目录
    if (!filedir.exists()) {
        filedir.mkdir();
    }

    // 创建文件名
    sb.append(context.getString(
            fileNameFormatResId,
            DateFormat.format(context.getString(R.string.format_date_ymd),
                    System.currentTimeMillis()))); 

    File file = new File(sb.toString());
    try {
        // 创建文件
        if (!file.exists()) {
            file.createNewFile();
        }
        return file;
    } catch (SecurityException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    return null;
}