datax的json中写参数

在datax的中，可以使用${}来引用参数。其中，参数可以在命令行中使用-p参数传递，也可以在job.json文件中定义。下面是一个示例：

{
    "job": {
        "setting": {
            "speed": {
                "channel": 3
            }
        },
        "content": [
            {
                "reader": {
                    "name": "mysqlreader",
                    "parameter": {
                        "username": "${username}",
                        "password": "${password}",
                        "column": [
                            "id",
                            "name"
                        ],
                        "where": "id > ${min_id} and id < ${max_id}"
                    }
                },
                "writer": {
                    "name": "mysqlwriter",
                    "parameter": {
                        "username": "${username}",
                        "password": "${password}",
                        "column": [
                            "id",
                            "name"
                        ],
                        "preSql": "delete from test where id > ${min_id} and id < ${max_id}",
                        "connection": [
                            {
                                "jdbcUrl": "jdbc:mysql://localhost:3306/test",
                                "table": [
                                    "test"
                                ]
                            }
                        ]
                    }
                }
            }
        ]
    }
}

在上面的示例中，可以看到where属性中使用了${min_id}和${max_id}两个参数。这两个参数可以在命令行中使用-p参数传递，例如：

nohup /usr/bin/python2 ${DATAX_PATH}/datax.py -p "-Dmin_id=100 -Dmax_id=200" job.json &

也可以在job.json文件中定义，例如：

{
    "job": {
        "setting": {
            "speed": {
                "channel": 3
            }
        },
        "content": [
            {
                "reader": {
                    "name": "mysqlreader",
                    "parameter": {
                        "username": "${username}",
                        "password": "${password}",
                        "column": [
                            "id",
                            "name"
                        ],
                        "where": "id > ${min_id} and id < ${max_id}"
                    }
                },
                "writer": {
                    "name": "mysqlwriter",
                    "parameter": {
                        "username": "${username}",
                        "password": "${password}",
                        "column": [
                            "id",
                            "name"
                        ],
                        "preSql": "delete from test where id > ${min_id} and id < ${max_id}",
                        "connection": [
                            {
                                "jdbcUrl": "jdbc:mysql://localhost:3306/test",
                                "table": [
                                    "test"
                                ]
                            }
                        ]
                    }
                }
            }
        ]
    },
    "jobExtendInfo": {
        "min_id": 100,
        "max_id": 200
    }
}

在上面的示例中，可以看到job.json文件中定义了min_id和max_id两个参数。这两个参数可以在命令行中不传递，datax会自动读取job.json文件中的定义。如果命令行中传递了-p参数，则会覆盖job.json文件中的定义。