应用场景

已有的、某类型数据（如行政区域关系）保存在sqlite中，sqlite数据库文件保存在assets目录下，APP需要读取该数据库中的数据

工具

GreenDao3.2

实例

AndroidGreenDaoAssetsDbExample

要点介绍

APP无法直接读取assets中数据库，必须将数据库复制到APP的数据库文件存储目录，这里注意需要判断目标文件夹中如果已经存在同名的数据库文件，则不再复制，避免重复执行复制数据库逻辑。

/**
     * Copies your database from your local assets-folder to the just created
     * empty database in the system folder, from where it can be accessed and
     * handled. This is done by transfering bytestream.
     * */
    private void copyDataBase(String dbname) throws IOException {
        // Open your local db as the input stream
        InputStream myInput = this.getAssets().open(dbname);
        // Path to the just created empty db
        File outFileName = this.getDatabasePath(dbname);

        if (!outFileName.exists()) {
            outFileName.getParentFile().mkdirs();

            // Open the empty db as the output stream
            OutputStream myOutput = new FileOutputStream(outFileName);
            // transfer bytes from the inputfile to the outputfile
            byte[] buffer = new byte[1024];
            int length;
            while ((length = myInput.read(buffer)) > 0) {
                myOutput.write(buffer, 0, length);
            }
            // Close the streams
            myOutput.flush();
            myOutput.close();
            myInput.close();
        }
    }

在Application的onCreate中，调用上述方法

        //复制assets目录下的数据库文件到应用数据库中
        try {
            copyDataBase("zone.db");
        } catch (Exception e) {
            Log.e("Application", e.getMessage());
        }

GreenDao的Entity一定要设置nameInDb，否则会读不到数据

@Entity(
        nameInDb = "town",
        createInDb = false
)
public class Town {

    @Id
    @Property(nameInDb = "id")
    private Long id;

    @Property(nameInDb = "name")
    private String name;
    @Property(nameInDb = "code")
    private int code;
    @Generated(hash = 62109782)
    public Town(Long id, String name, int code) {
        this.id = id;
        this.name = name;
        this.code = code;
    }
    @Generated(hash = 2030923556)
    public Town() {
    }
    public Long getId() {
        return this.id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        return this.name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getCode() {
        return this.code;
    }
    public void setCode(int code) {
        this.code = code;
    }

}