出发点：
当然是由于编程习惯太好，打了一堆中文log，其实只是想给测试看。然而如果包被反编译，看log基本都能理解流程了，有点尴尬。所以此文主要探究proguard配置，以去除log。
以下过程示例，来自于这段代码。
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
private String a = "a";
private String b = "b";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.d(TAG, "This is" + a + b);
}
}
啥都不配置的情况下，反编译的smali代码如下：
# virtual methods
.method public onCreate(Landroid/os/Bundle;)V
.locals 2
invoke-super {p0, p1}, Landroid/support/v7/app/c;->onCreate(Landroid/os/Bundle;)V
const p1, 0x7f09001b
invoke-virtual {p0, p1}, Lcom/rentee/logremove/MainActivity;->setContentView(I)V
const-string p1, "MainActivity"
new-instance v0, Ljava/lang/StringBuilder;
const-string v1, "This is"
invoke-direct {v0, v1}, Ljava/lang/StringBuilder;-><init>(Ljava/lang/String;)V
iget-object v1, p0, Lcom/rentee/logremove/MainActivity;->m:Ljava/lang/String;
invoke-virtual {v0, v1}, Ljava/lang/StringBuilder;->append(Ljava/lang/String;)Ljava/lang/StringBuilder;
iget-object v1, p0, Lcom/rentee/logremove/MainActivity;->n:Ljava/lang/String;
invoke-virtual {v0, v1}, Ljava/lang/StringBuilder;->append(Ljava/lang/String;)Ljava/lang/StringBuilder;
invoke-virtual {v0}, Ljava/lang/StringBuilder;->toString()Ljava/lang/String;
move-result-object v0
invoke-static {p1, v0}, Landroid/util/Log;->d(Ljava/lang/String;Ljava/lang/String;)I
return-void
.end method
很明显，整条字符串拼接过程是由StringBuilder完成的。
1.在build.gradle配置proguard-android-optimize.txt，因为默认的proguard-android.txt优化开关是关了的，而proguard的assumenosideeffects、
assumenoexternalsideeffects配置是需要开启优化开关的。
buildTypes {
release {
minifyEnabled true
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
}
}
在proguard-rules.pro文件中配置assumenosideeffects。这是网上的通用大解。
-assumenosideeffects class android.util.Log {
public static boolean isLoggable(java.lang.String, int);
public static int v(...);
public static int i(...);
public static int w(...);
public static int d(...);
public static int e(...);
}
不过也的确存在一个问题，就是去除不干净，反编译后，smail如下：
# virtual methods
.method public onCreate(Landroid/os/Bundle;)V
.locals 1
invoke-super {p0, p1}, Landroid/support/v7/app/c;->onCreate(Landroid/os/Bundle;)V
const p1, 0x7f09001b
invoke-virtual {p0, p1}, Lcom/rentee/logremove/MainActivity;->setContentView(I)V
new-instance p1, Ljava/lang/StringBuilder;
const-string v0, "This is"
invoke-direct {p1, v0}, Ljava/lang/StringBuilder;-><init>(Ljava/lang/String;)V
iget-object v0, p0, Lcom/rentee/logremove/MainActivity;->m:Ljava/lang/String;
invoke-virtual {p1, v0}, Ljava/lang/StringBuilder;->append(Ljava/lang/String;)Ljava/lang/StringBuilder;
iget-object v0, p0, Lcom/rentee/logremove/MainActivity;->n:Ljava/lang/String;
invoke-virtual {p1, v0}, Ljava/lang/StringBuilder;->append(Ljava/lang/String;)Ljava/lang/StringBuilder;
return-void
.end method
Log的相关代码没了，但是还是有StringBuilder的拼接过程在，这个从根本上解决不了问题。
2.进化版，proguard 6.0以上版本新增了assumenoexternalsideeffects和assumenoexternalreturnvalues，这两个属性6.0才引入，Android自带proguard-gradle插件并没有这么新，所以要在工程项目根目录配置如下strategy，强制将progurad指定到6.0以上版本。
buildscript {
configurations.all {
resolutionStrategy {
force "net.sf.proguard:proguard-gradle:6.0.3"
}
}
}
然后在progaurd-rules.txt文件中增加如下配置：
-assumenoexternalsideeffects class java.lang.StringBuilder {
public java.lang.StringBuilder();
public java.lang.StringBuilder(int);
public java.lang.StringBuilder(java.lang.String);
public java.lang.StringBuilder append(java.lang.Object);
public java.lang.StringBuilder append(java.lang.String);
public java.lang.StringBuilder append(java.lang.StringBuffer);
public java.lang.StringBuilder append(char[]);
public java.lang.StringBuilder append(char[], int, int);
public java.lang.StringBuilder append(boolean);
public java.lang.StringBuilder append(char);
public java.lang.StringBuilder append(int);
public java.lang.StringBuilder append(long);
public java.lang.StringBuilder append(float);
public java.lang.StringBuilder append(double);
public java.lang.String toString();
}
-assumenoexternalreturnvalues public final class java.lang.StringBuilder {
public java.lang.StringBuilder append(java.lang.Object);
public java.lang.StringBuilder append(java.lang.String);
public java.lang.StringBuilder append(java.lang.StringBuffer);
public java.lang.StringBuilder append(char[]);
public java.lang.StringBuilder append(char[], int, int);
public java.lang.StringBuilder append(boolean);
public java.lang.StringBuilder append(char);
public java.lang.StringBuilder append(int);
public java.lang.StringBuilder append(long);
public java.lang.StringBuilder append(float);
public java.lang.StringBuilder append(double);
}
这段配置的作用是，去除返回值无用的StringBuilder的相关操作，由于在第2点配置后，Log相关代码被去除，所以Log中的字符串拼接也是无用的，会被去除。配置后smali代码是：
# virtual methods
.method public onCreate(Landroid/os/Bundle;)V
.locals 0
invoke-super {p0, p1}, Landroid/support/v7/app/c;->onCreate(Landroid/os/Bundle;)V
const p1, 0x7f09001b
invoke-virtual {p0, p1}, Lcom/rentee/logremove/MainActivity;->setContentView(I)V
return-void
.end method
是的，一句都没有了，干干净净，爽！
proguard官方英文原文地址：
https://www.guardsquare.com/en/proguard/manual/examples#logging
原文发布时间为：2018-10-10
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