System源码浅析- initializeSystemClass(setXXX0)

痴货笑话而已

已于 2022-05-14 12:09:20 修改

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分类专栏：源码学习文章标签： java

于 2022-05-13 18:44:01 首次发布

本文链接：https://blog.youkuaiyun.com/DramaLifes/article/details/124757637

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本文深入探讨Java的System类，重点关注setIn0、setOut0和setErr0方法的实现细节，包括Java_java_lang_System_setIn0、setOut0和setErr0的调用过程，以及GetStaticFieldID和SetStaticObjectField在初始化System类中的作用。

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文章目录

前情提要

在前面已经介绍过 System与initializeSystemClass 在此不做过多解释，没有看到的希望去查看！
System源码浅析- initializeSystemClass(initProperties)
System源码浅析- initializeSystemClass(saveAndRemoveProperties)
System源码浅析- initializeSystemClass(setXXX0)
System源码浅析- initializeSystemClass(loadLibrary)
System源码浅析- initializeSystemClass(setup)
System源码浅析- initializeSystemClass( initializeOSEnvironment )
System源码浅析- initializeSystemClass( setJavaLangAccess)

setIn0

Java_java_lang_System_setIn0

Java_java_lang_System_setIn0(JNIEnv *env, jclass cla, jobject stream)
{
    /*
    jfieldID (JNICALL *GetStaticFieldID)
      (JNIEnv *env, jclass clazz, const char *name, const char *sig);
      
     jfieldID GetStaticFieldID(jclass clazz, const char *name,
                              const char *sig) {
        return functions->GetStaticFieldID(this,clazz,name,sig);
    }
    */
    jfieldID fid =
        (*env)->GetStaticFieldID(env,cla,"in","Ljava/io/InputStream;");
    if (fid == 0)
        return;
    /*
    void (JNICALL *SetStaticObjectField)
      (JNIEnv *env, jclass clazz, jfieldID fieldID, jobject value);
      
     void SetStaticObjectField(jclass clazz, jfieldID fieldID,
                        jobject value) {
      functions->SetStaticObjectField(this,clazz,fieldID,value);
    }
    */
    (*env)->SetStaticObjectField(env,cla,fid,stream);
}

setOut0

Java_java_lang_System_setOut0

Java_java_lang_System_setOut0(JNIEnv *env, jclass cla, jobject stream)
{
    jfieldID fid =
        (*env)->GetStaticFieldID(env,cla,"out","Ljava/io/PrintStream;");
    if (fid == 0)
        return;
    (*env)->SetStaticObjectField(env,cla,fid,stream);
}

setErr0

Java_java_lang_System_setErr0

Java_java_lang_System_setErr0(JNIEnv *env, jclass cla, jobject stream)
{
    jfieldID fid =
        (*env)->GetStaticFieldID(env,cla,"err","Ljava/io/PrintStream;");
    if (fid == 0)
        return;
    (*env)->SetStaticObjectField(env,cla,fid,stream);
}

GetStaticFieldID

    jfieldID (JNICALL *GetStaticFieldID)
      (JNIEnv *env, jclass clazz, const char *name, const char *sig);
      
     jfieldID GetStaticFieldID(jclass clazz, const char *name,
                              const char *sig) {
        return functions->GetStaticFieldID(this,clazz,name,sig);
    }

SetStaticObjectField

    void (JNICALL *SetStaticObjectField)
      (JNIEnv *env, jclass clazz, jfieldID fieldID, jobject value);
      
     void SetStaticObjectField(jclass clazz, jfieldID fieldID,
                        jobject value) {
      functions->SetStaticObjectField(this,clazz,fieldID,value);
    }