MD5简单实例

如图当点击按钮时，会先判断是否第一次登陆，如果是第一次登陆登陆则会弹出设置密码的弹窗，若果登陆过则弹出登陆弹窗

其中输入的密码会用MD5加密下

package com.org.demo.wangfeng.demo;

import com.org.wangfeng.R;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class HomeActivity extends Activity {
    private Button bbButton;
    private SharedPreferences mPref;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.homeactivity);
        mPref = getSharedPreferences("config", MODE_PRIVATE);
        bbButton = (Button) findViewById(R.id.bb_home);
        bbButton.setOnClickListener(new OnclickItem());
    }

    private class OnclickItem implements View.OnClickListener {

        @Override
        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            String savedPassword = mPref.getString("password", null);
            if(!TextUtils.isEmpty(savedPassword)){
                //输入密码弹窗
                showPasswordInputDialog();
            }else{
                //如果没有设置过，弹出设置密码的弹窗
                showPasswordSetDialog();
            }
        }

    }

    /**
     * 设置密码的弹窗
     */
    private void showPasswordSetDialog() {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        final AlertDialog dialog = builder.create();
        View view = View.inflate(this, R.layout.dialog_set_password, null);
        dialog.setView(view, 0, 0, 0, 0);// 设置边距为0,保证在2.x的版本上运行没问题

        final EditText edPassWord = (EditText) view
                .findViewById(R.id.et_password);
        final EditText edPassWordConfirm = (EditText) view
                .findViewById(R.id.et_password_confirm);

        Button btnOK = (Button) view.findViewById(R.id.btn_ok);
        Button btnCancel = (Button) view.findViewById(R.id.btn_cancel);

        btnOK.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                String password = edPassWord.getText().toString().trim();
                String passwordConfirm = edPassWordConfirm.getText().toString().trim();
                if (!TextUtils.isEmpty(password) && !passwordConfirm.isEmpty()) {
                    // 当输入的2个内容相同
                    if (password.equals(passwordConfirm)) {
                        Toast.makeText(HomeActivity.this, "登陆成功",
                                Toast.LENGTH_SHORT).show();
                        // 将密码保存起来
                        mPref.edit()
                                .putString("password",
                                        MD5Utils.encode(password)).commit();
                        dialog.dismiss();
                    } else {
                        Toast.makeText(HomeActivity.this, "2此输入密码不一致",
                                Toast.LENGTH_SHORT).show();
                    }
                } else {
                    Toast.makeText(HomeActivity.this, "输入内容不能为空",
                            Toast.LENGTH_SHORT).show();
                }
            }
        });
        btnCancel.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                dialog.dismiss();
            }
        });
        dialog.show();
    }

    /**
     * 输入密码弹窗
     */
    private void showPasswordInputDialog() {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        final AlertDialog dialog = builder.create();
        View view = View.inflate(this, R.layout.dialog_input_password, null);
        dialog.setView(view, 0, 0, 0, 0);
        final EditText etPassword = (EditText) view
                .findViewById(R.id.et_password);

        Button btnOk = (Button) view.findViewById(R.id.btn_ok);
        Button btnCancel = (Button) view.findViewById(R.id.btn_cancel);
        btnOk.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                String password = etPassword.getText().toString().trim();
                if (!TextUtils.isEmpty(password)) {
                    String savedPassword = mPref.getString("password", null);
                    if (MD5Utils.encode(password).equals(savedPassword)) {
                        Toast.makeText(HomeActivity.this, "登陆成功",
                                Toast.LENGTH_SHORT).show();
                        dialog.dismiss();
                    } else {
                        Toast.makeText(HomeActivity.this, "密码错误",
                                Toast.LENGTH_SHORT).show();
                    }
                } else {
                    Toast.makeText(HomeActivity.this, "输入内容不能为空",
                            Toast.LENGTH_SHORT).show();
                }
            }
        });
        btnCancel.setOnClickListener(new View.OnClickListener() {
            
            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                dialog.dismiss();
            }
        });
        dialog.show();
    }
}

package com.org.demo.wangfeng.demo;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5Utils {
    /**
     * md5加密
     * 
     * @param password
     * @return
     */
    public static String encode(String password) {
        try {
            MessageDigest instance = MessageDigest.getInstance("MD5");// 获取MD5算法对象
            byte[] digest = instance.digest(password.getBytes());// 对字符串加密,返回字节数组

            StringBuffer sb = new StringBuffer();
            for (byte b : digest) {
                int i = b & 0xff;// 获取字节的低八位有效值
                String hexString = Integer.toHexString(i);// 将整数转为16进制

                if (hexString.length() < 2) {
                    hexString = "0" + hexString;// 如果是1位的话,补0
                }

                sb.append(hexString);
            }

            return sb.toString();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
            // 没有该算法时,抛出异常, 不会走到这里
        }

        return "";
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#fff"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="#66ff6600"
        android:gravity="center"
        android:padding="10dp"
        android:text="设置密码"
        android:textColor="@android:color/black"
        android:textSize="20sp" />

    <EditText
        android:id="@+id/et_password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入密码"
        android:inputType="textPassword" >
    </EditText>

    <EditText
        android:id="@+id/et_password_confirm"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请再次输入密码"
        android:inputType="textPassword" >
    </EditText>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <Button
            android:id="@+id/btn_ok"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="确定" />

        <Button
            android:id="@+id/btn_cancel"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="取消" />
    </LinearLayout>

</LinearLayout>

其实在android里 if(text ==null || text.length()==0)是有封装的。
在android.text.TextUtils里

public static boolean isEmpty(CharSequence str) {
        if (str == null || str.length() == 0)
            return true;
        else
            return false;
    }
所以我们可以使用

TextUtils.isEmpty(text)

代替

if(text == null || text.length() == 0)