详解将jsoncpp编译so库，进行封装和解析JSON数据

以你之姓@ 2022-06-08 10:00 1123阅读 0赞

![20170921221352077][]

作者：谭东

时间：2017年9月21日

环境：Windows 8.1

NDK版本：android-ndk-r14b

工具：Android Studio2.3.3

有的时候我们需要在封装的so库里把要获取到的信息转为json格式输出，或者解析外部传入进来的json数据，那么C++里一般使用jsoncpp库来实现。

jsoncpp 是比较出名的 C++ JSON 解析库。在 JSON官网也是首推的。源码下载链接：[http://jsoncpp.sourceforge.net/][http_jsoncpp.sourceforge.net]

下面就给大家讲解jsoncpp的编译和简单使用。编译出的so库可以供Android使用。其他平台大同小异。

1、下载jsoncpp源码。可以在github上下载到：[https://github.com/open-source-parsers/jsoncpp][https_github.com_open-source-parsers_jsoncpp]

下载后，jsoncpp的大致目录如下图。

![20170921224525711][]

主要关注include和src目录下的lib\_json这两个文件夹。

include里是.h头文件，src目录下的lib\_json里是.cpp源文件。

![20170921224642674][]

![20170921224653366][]

2、用Android Studio新建一个支持c++的项目。在项目的libs目录下新建libjson文件夹，将include里的json文件夹里的.h头文件拷贝进去，并将src/lib\_json下的.cpp和.inl及.h文件也拷贝进去。

![20170921225424564][]

导入后可能会报错，引入的头文件路径不对，那么就按照提示进行修改和导入相应的头文件即可。

3、接下来，我们需要把我的源文件加入到列表，供CMake编译。编辑我们的CMakeLists.txt，如下面所示。

# For more information about using CMake with Android Studio, read the
    # documentation: https://d.android.com/studio/projects/add-native-code.html
    
    # Sets the minimum version of CMake required to build the native library.
    
    cmake_minimum_required(VERSION 3.4.1)
    
    # Creates and names a library, sets it as either STATIC
    # or SHARED, and provides the relative paths to its source code.
    # You can define multiple libraries, and CMake builds them for you.
    # Gradle automatically packages shared libraries with your APK.
    
    
    add_library( json
                 SHARED
                 libs/include/libjson/json_reader.cpp
                 libs/include/libjson/json_value.cpp
                 libs/include/libjson/json_writer.cpp)
    
    add_library( # Sets the name of the library.
                 native-lib
    
                 # Sets the library as a shared library.
                 SHARED
    
                 # Provides a relative path to your source file(s).
                 src/main/cpp/native-lib.cpp )
    
    # Searches for a specified prebuilt library and stores the path as a
    # variable. Because CMake includes system libraries in the search path by
    # default, you only need to specify the name of the public NDK library
    # you want to add. CMake verifies that the library exists before
    # completing its build.
    
    find_library( # Sets the name of the path variable.
                  log-lib
    
                  # Specifies the name of the NDK library that
                  # you want CMake to locate.
                  log )
    set(distribution_DIR ${CMAKE_SOURCE_DIR}/../../../../libs)
    # Specifies libraries CMake should link to your target library. You
    # can link multiple libraries, such as libraries you define in this
    # build script, prebuilt third-party libraries, or system libraries.
    
    target_link_libraries( # Specifies the target library.
                           native-lib
                           json
                           # Links the target library to the log library
                           # included in the NDK.
                           ${log-lib} )

4、编译我们的源码，生成相应的so库。

![20170921225719465][]

5、编译好后，我们就可以查看到so库了。

如果编译中遇到这种错误提示，我们只需把include的头文件的<>改成“”即可。

![20170921230104920][]

![20170921230158397][]

注意，这里的json\_tool.h要改下，正确的为：

// Copyright 2007-2010 Baptiste Lepilleur
    // Distributed under MIT license, or public domain if desired and
    // recognized in your jurisdiction.
    // See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE
    
    #ifndef LIB_JSONCPP_JSON_TOOL_H_INCLUDED
    #define LIB_JSONCPP_JSON_TOOL_H_INCLUDED
    #include <clocale>
    
    /* This header provides common string manipulation support, such as UTF-8,
     * portable conversion from/to string...
     *
     * It is an internal header that must not be exposed.
     */
    
    namespace Json {
    
    /// Fallback for decimal_point on android, where the lconv is an empty struct.
        template<typename Lconv, bool=(sizeof(Lconv) >= sizeof(char*))>
        struct Locale {
            static char decimalPoint() {
                return '\0';
            }
        };
    
    /// Return decimal_point for the current locale.
        template<typename Lconv>
        struct Locale<Lconv, true> {
            static char decimalPoint() {
                Lconv* lc = localeconv();
                if (lc == NULL) {
                    return '\0';
                }
                return *(lc->decimal_point);
            }
        };
    
    /// Converts a unicode code-point to UTF-8.
        static inline JSONCPP_STRING codePointToUTF8(unsigned int cp) {
            JSONCPP_STRING result;
    
            // based on description from http://en.wikipedia.org/wiki/UTF-8
    
            if (cp <= 0x7f) {
                result.resize(1);
                result[0] = static_cast<char>(cp);
            } else if (cp <= 0x7FF) {
                result.resize(2);
                result[1] = static_cast<char>(0x80 | (0x3f & cp));
                result[0] = static_cast<char>(0xC0 | (0x1f & (cp >> 6)));
            } else if (cp <= 0xFFFF) {
                result.resize(3);
                result[2] = static_cast<char>(0x80 | (0x3f & cp));
                result[1] = static_cast<char>(0x80 | (0x3f & (cp >> 6)));
                result[0] = static_cast<char>(0xE0 | (0xf & (cp >> 12)));
            } else if (cp <= 0x10FFFF) {
                result.resize(4);
                result[3] = static_cast<char>(0x80 | (0x3f & cp));
                result[2] = static_cast<char>(0x80 | (0x3f & (cp >> 6)));
                result[1] = static_cast<char>(0x80 | (0x3f & (cp >> 12)));
                result[0] = static_cast<char>(0xF0 | (0x7 & (cp >> 18)));
            }
    
            return result;
        }
    
    /// Returns true if ch is a control character (in range [1,31]).
        static inline bool isControlCharacter(char ch) { return ch > 0 && ch <= 0x1F; }
    
        enum {
            /// Constant that specify the size of the buffer that must be passed to
            /// uintToString.
                    uintToStringBufferSize = 3 * sizeof(LargestUInt) + 1
        };
    
    // Defines a char buffer for use with uintToString().
        typedef char UIntToStringBuffer[uintToStringBufferSize];
    
    /** Converts an unsigned integer to string.
     * @param value Unsigned interger to convert to string
     * @param current Input/Output string buffer.
     *        Must have at least uintToStringBufferSize chars free.
     */
        static inline void uintToString(LargestUInt value, char*& current) {
            *--current = 0;
            do {
                *--current = static_cast<char>(value % 10U + static_cast<unsigned>('0'));
                value /= 10;
            } while (value != 0);
        }
    
    /** Change ',' to '.' everywhere in buffer.
     *
     * We had a sophisticated way, but it did not work in WinCE.
     * @see https://github.com/open-source-parsers/jsoncpp/pull/9
     */
        static inline void fixNumericLocale(char* begin, char* end) {
            while (begin < end) {
                if (*begin == ',') {
                    *begin = '.';
                }
                ++begin;
            }
        }
    
        static inline void fixNumericLocaleInput(char* begin, char* end) {
            char decimalPoint = Locale<struct lconv>::decimalPoint();
            if (decimalPoint != '\0' && decimalPoint != '.') {
                while (begin < end) {
                    if (*begin == '.') {
                        *begin = decimalPoint;
                    }
                    ++begin;
                }
            }
        }
    
    } // namespace Json {
    
    #endif // LIB_JSONCPP_JSON_TOOL_H_INCLUDED

为什么修改请看官方这里： [https://github.com/open-source-parsers/jsoncpp/pull/523][https_github.com_open-source-parsers_jsoncpp_pull_523]

修改方案看这里：[https://github.com/open-source-parsers/jsoncpp/blob/52cfe5ae889adf0c4099b16ddeb4b529b1f09007/src/lib\_json/json\_tool.h][https_github.com_open-source-parsers_jsoncpp_blob_52cfe5ae889adf0c4099b16ddeb4b529b1f09007_src_lib_json_json_tool.h]  
编译后的so库如下图所示：

![20170921233855155][]

6、简单的使用方法：

#include <jni.h>
    #include <string>
    #include "../../../libs/include/libjson/value.h"
    
    extern "C" {
    
    JNIEXPORT jstring JNICALL
    Java_com_tandong_jsoncpp_MainActivity_stringFromJNI(
            JNIEnv *env,
            jobject /* this */) {
        std::string hello = "Hello from C++";
        return env->NewStringUTF(hello.c_str());
    }
    
    JNIEXPORT jstring JNICALL
    Java_com_tandong_jsoncpp_MainActivity_stringFromJNI2(
            JNIEnv *env,
            jobject /* this */) {
        Json::Value video;
        video["id"] = 1;
        video["name"] = "名字";
        const char *json_str = video.toStyledString().c_str();
        jstring result = env->NewStringUTF(json_str);
        return result;
    }
    
    }

注意jsoncpp不支持long型，支持double等其他类型。

7、如果我想把libjson.so放在其他项目引用使用怎么办？请往下看。假如我们新建个项目，需要用到libjson.so，并且重新编译使用了libjson.so库的so库。没听懂？看下图：

![20170922195420811][]

先把上面编译后的libjson.so拷贝到新项目src/main/jniLibs/armeabi  里，即对应的so库文件夹里。

然后把jsoncpp源码include里的.h文件拷贝到新项目的libs/include/libjson/下面。

如下图所示：

![20170922195910054][]

接下来编写配置CMakeList.txt：

# For more information about using CMake with Android Studio, read the
    # documentation: https://d.android.com/studio/projects/add-native-code.html
    
    # Sets the minimum version of CMake required to build the native library.
    
    cmake_minimum_required(VERSION 3.4.1)
    
    # Creates and names a library, sets it as either STATIC
    # or SHARED, and provides the relative paths to its source code.
    # You can define multiple libraries, and CMake builds them for you.
    # Gradle automatically packages shared libraries with your APK.
    
    set(distribution_DIR ${CMAKE_SOURCE_DIR}/../../../../libs)
    
    
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")
    
    
    add_library( json
                 SHARED
                 IMPORTED )
    
    
    set_target_properties( json
                           PROPERTIES IMPORTED_LOCATION
                           ../../../../src/main/jniLibs/armeabi/libjson.so )
    
    
    add_library( # Sets the name of the library.
                 native-lib
    
                 # Sets the library as a shared library.
                 SHARED
    
                 # Provides a relative path to your source file(s).
                 src/main/cpp/native-lib.cpp )
    
    # Searches for a specified prebuilt library and stores the path as a
    # variable. Because CMake includes system libraries in the search path by
    # default, you only need to specify the name of the public NDK library
    # you want to add. CMake verifies that the library exists before
    # completing its build.
    
    find_library( # Sets the name of the path variable.
                  log-lib
    
                  # Specifies the name of the NDK library that
                  # you want CMake to locate.
                  log )
    
    # Specifies libraries CMake should link to your target library. You
    # can link multiple libraries, such as libraries you define in this
    # build script, prebuilt third-party libraries, or system libraries.
    
    include_directories(libs/include)
    
    target_link_libraries( # Specifies the target library.
                           native-lib
                           json
                           # Links the target library to the log library
                           # included in the NDK.
                           ${log-lib} )

然后编写jni的cpp方法：

#include <jni.h>
    #include <string>
    #include "../../../libs/include/libjson/value.h"
    
    extern "C" {
    
    JNIEXPORT jstring JNICALL
    Java_com_tandong_jsoncppdemo_MainActivity_stringFromJNI(
            JNIEnv *env,
            jobject /* this */) {
        std::string hello = "Hello from C++";
        return env->NewStringUTF(hello.c_str());
    }
    
    JNIEXPORT jstring JNICALL
    Java_com_tandong_jsoncppdemo_MainActivity_stringFromJNI2(
            JNIEnv *env,
            jobject /* this */) {
        Json::Value video;
        video["id"] = 1;
        video["name"] = "名字";
        const char *json_str = video.toStyledString().c_str();
        jstring result = env->NewStringUTF(json_str);
        return result;
    }
    
    }

再附上build.gradle的配置：

apply plugin: 'com.android.application'
    
    android {
        compileSdkVersion 26
        buildToolsVersion "26.0.1"
        defaultConfig {
            applicationId "com.tandong.jsoncppdemo"
            minSdkVersion 15
            targetSdkVersion 26
            versionCode 1
            versionName "1.0"
            testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
            externalNativeBuild {
                cmake {
                    cppFlags ""
                }
            }
            ndk{
                abiFilters 'armeabi'
            }
        }
        buildTypes {
            release {
                minifyEnabled false
                proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
            }
        }
        externalNativeBuild {
            cmake {
                path "CMakeLists.txt"
            }
        }
    }
    
    dependencies {
        compile fileTree(dir: 'libs', include: ['*.jar'])
        androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
            exclude group: 'com.android.support', module: 'support-annotations'
        })
        compile 'com.android.support:appcompat-v7:26.+'
        compile 'com.android.support.constraint:constraint-layout:1.0.2'
        testCompile 'junit:junit:4.12'
    }

效果如图：

![20170922200321868][]

其他的编写方法一样，敬请关注。

微信公众号：

![20170830212011034][]

[20170921221352077]: /images/20220608/e30a227ce25241f4b0ff27a7f3aea423.png
[http_jsoncpp.sourceforge.net]: http://jsoncpp.sourceforge.net/
[https_github.com_open-source-parsers_jsoncpp]: https://github.com/open-source-parsers/jsoncpp
[20170921224525711]: /images/20220608/f924ae238ea6405ea8daabca31abcf99.png
[20170921224642674]: /images/20220608/fec5942567a54eab9b8ee2c9bd5ecd98.png
[20170921224653366]: /images/20220608/8cd8f89dc0354a19950ce4e41f955bf0.png
[20170921225424564]: /images/20220608/edb020ede95a4de8bdb050477e837a4f.png
[20170921225719465]: /images/20220608/1fb0642b7d3847c2a128332e43cd4020.png
[20170921230104920]: /images/20220608/6db25705efa348409880f5c53622fc2e.png
[20170921230158397]: /images/20220608/d99e16108f7341a8ab4d30351c41bf30.png
[https_github.com_open-source-parsers_jsoncpp_pull_523]: https://github.com/open-source-parsers/jsoncpp/pull/523
[https_github.com_open-source-parsers_jsoncpp_blob_52cfe5ae889adf0c4099b16ddeb4b529b1f09007_src_lib_json_json_tool.h]: https://github.com/open-source-parsers/jsoncpp/blob/52cfe5ae889adf0c4099b16ddeb4b529b1f09007/src/lib_json/json_tool.h
[20170921233855155]: /images/20220608/f8b0b24966b643a380f7f2239e9092c8.png
[20170922195420811]: /images/20220608/9b86bcee7d93437c8e012c5f227be451.png
[20170922195910054]: /images/20220608/d7d83a4e92e94e6da1b3fd10ac938b6d.png
[20170922200321868]: /images/20220608/056524e089df467ab86f46648ad7c4a8.png
[20170830212011034]: /images/20220608/98b1338cd3af486cbc0ebf248718be50.png